Research Activities
in
NTT Basic Research Laboratories
Volume 15
Fiscal 2004

June 2005
NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation (NTT)http://www.brl.ntt.co.jp

Outer mirror{11-22} microfacetPelectrode

Cavity mirror{11-20} microfacet

InGaN-based horizontal cavity surface emitting laser diodeElectrometer

Single-electron
turnstile

Single-electron turnstile

Electrometer current [nA]

An SEM bird’s-eye-view photograph of an InGaN-based horizontal cavity surface emitting
laser diode (HCSELD). A Fabry-Perot cavity mirror and an outer micromirror are a vertical{11-20} microfacet and an inclined {11-22} microfacet of the regrown Mg-doped GaN layers,respectively. The {11-20} Fabry-Perot cavity mirror of the HCSELD is vertical to a SiC
substrate. The angle between the inclined {11-22} outer micromirror and the SiC substratesurface is 58 degrees. Therefore, geometrically, laser beams are emitted at an angle of 64
degrees to the substrate surface. The InGaN-based HCSELDs lase at room temperature bycurrent injection. (page 1 8)

Electron microscope image

Transfer time:<10ns
Retention time:>104s

0

0.98

1
0.96

2
3
4
Room temp.
# of electrons： 5

0.94
0.92

0

1 2 3 4 5 6# of transfer cycles

Single-electrontransfer and detection

Room-temperature single-electron transfer and detection
with silicon nanodevices
Transfer and subsequent detection of single electrons are demonstrated at room temperatureusing a silicon-on-insulator nanodevice. The turnstile, which is composed of two Si-wire-FETs
with a fine gate, enables us to transfer single electrons by opening and closing the two FETs
alternately. The transferred individual electrons are stored in a memory node and detected byan electrometer with single-electron resolution. The size reduction and optimized operating
conditions allow the room-temperature operation. The present device achieves high-speedtransfer and long retention. We demonstrated that the device could serve as a multi-level
single-electron memory. (page 30)

50
45

P sw [%]

1

0

40
35

1
(| 0 > + | 1 > )2Circulating current in a qubit
Clockwise, anti-clockwise andsuperposition states are shown.

30
1.0

Schrödinger’s cat
Facing left and right and thesesuperposition are shown. Can
macroscopic scale object exhibit
such superposition?

1.2

1.4

1.6

∆'t12 [ns]1.8

Quantum coherent oscillation
Quantum mechanical states arecontrolled by relative phase between
two microwave pulses.

Fast control of qubit coherence with phase shift method
A superconductor ring with Josephson junctions behaves as a quantum 2-level system and is
expected to be a candidate for a quantum bit (qubit), which is a key ingredient of a quantum
computer. The size of the ring is about 10μm, which is much larger than atoms or molecules
but it still shows quantum nature of the 2-level system. The quantum superposition in such amacroscopic scale object is sometimes called Schrödinger’s cat. (Page 36 )Cross-sectional SEM image of microcavity

2.0

Dispersion of InGaN cavity polariton

InGaN Cavity Polaritons
Cavity polaritons are quasi-particles that are created by strong exciton-photon coupling in asemiconductor microcavity. We successfully fabricated a high quality GaN-based
microcavity structure using the wafer bonding technique and formed InGaN cavity polaritonsat room temperature for the first time. (Page 44)

From Science to Innovative Technology
NTT Basic Research Laboratories is extremely
grateful for your interest in and support of its
research activities.
The mission of NTT BRL is to: 1) discover new
concepts in the field of network technology thatwould overcome the present limitations in speed,
capacity and size, and 2) develop basic
technologies that could lead to future (span of 5
to 20 years) commercial opportunities. Based on
this concept it has been focusing on quantum
information processing and nano-bio project.
The core research in information processing isquantum
computation
andquantum
cryptography. Taking advantage of its richexperience and knowledge in solid-state devices,
NTT BRL has been engaged in quantum bit
research using superconducting device, semiconductor quantum dot and cooled atom,
and achieving worldwide success. In recent years, research on quantum cryptographyusing novel algorithm has become another major focus. Another main research,nano-bio project, is conducted by fusing neuroscience, bio-molecular science andnanotechnology. Molecular - protein hybrid structure, for instance, could lead to novel
devices in the future.
While promoting these projects, it is implementing exploratory research in thefollowing fields: quantum correlation within low-dimensional electron systems, systems
that use the spin of individual electrons as an information carrier, material design thatuses quantum dots as building blocks, electrical properties of carbon nano-tubes, andMEMS (microelectromechanical systems) related to superconductivity.
It putsemphasis in having good communication between researchers and managers in order toprecisely judge the potential of each research.
Innovative technology is also carried out. For instance, BRL has succeeded inoperating a diamond transistor at 80GHz by developing technology to produce diamondthin films of high quality. In addition, core technologies, i.e. single-electron devices
which have extremely low power consumption, photonic crystal for use as active opticalcircuits, and electron devices using wide-bandgap semiconductor materials, are underresearch and considered to solve limitations in network.
Moreover, BRL not only keeps in close touch with other NTT Laboratories, but also
runs various scientific exchange programs with institutes inside and outside Japan.

It has been working on quantum dots and quantum bits together with Delft University
and Stanford University, which has been producing fruitful results. Collaboration in
nano-bio with University of Oxford has recently took off and is expected to achieve
success.
Other activities of BRL include International Symposiums, BRL School andInternational Advisory Board Meetings, which play roles to disseminate its researchworldwide and to encourage greater understanding of it.

June 2005

Dr. Hideaki Takayanagi
Director
NTT Basic Research Laboratories
3-1 Morinosato-Wakamiya, Atsugi-shi,
Kanagawa 243-0198, Japan
Phone: +81 46 240 3300
Fax: +81 46 270 2358
Email: takayanagi@nttbrl.jp

Contents
page

Member List ............................................................................................................................................ 1
I. Research Topics◆Overview of Research in Laboratories ................................................................................................... 15◆Materials Science Research.................................................................................................................... 16♦ Fabrication of Josephson junctions using MgB2
♦ InGaN quantum wells with high luminescent efficiency♦ An InGaN-based horizontal cavity surface emitting laser diode♦ Growth of High-Quality GaN Using Novel Buffer Layer♦ AlN field emission display♦ Real-time Observation of Nanowire Formation by Means of GISAXS♦ Synthesis of Functionalized Carbon Nanotubes using DNA and Gold Nanoparticles♦ Spatially Selective Removal of Carbon Nanotubes♦ Arrangement of Au-Si alloy islands at atomic steps♦ Development of a conducting polymer electrode and measurements of neural activity with amicroelectrode array♦ AFM observation of purified IP3 receptor protein♦ Photoresponse Behavior of Conjugated Polymer-Based Nano Device♦ Organotypic culture techniques and study of neural toxicity◆Quantum Electron Physics Research...................................................................................................... 29♦ First-principles Study of Interfacial Reaction Mechanism during Silicon Thermal Oxidation
Process♦ Room-temperature single-electron transfer and detection with silicon nanodevics♦ Integrated carbon multi-probe with nano-spring on Si cantilever♦ Force/Displacement Detection Using Electron Interference♦ Landau-level hybridization and the quantum Hall effect in InAs/GaSb electron-hole systems♦ Controlled Valley Splitting in SiO2/Si/SiO2 Quantum Wells♦ Single-Electron Counting of Electrical Current♦ Fast control of qubit coherence with phase shift method♦ Quantum Computation with Neutral Atoms♦ Spin Interferometer by the Rashba Spin-Orbit Interaction♦ Electron-Spin Control based on RKKY Interaction◆Quantum Optics and Optical Materials Research .................................................................................. 40♦ Generation of telecom-band polarization entangled photon pairs using spontaneous four-wave
mixing in dispersion-shifted fiber♦ Differential-phase-shift quantum key distribution experiment♦ Time-resolved EXAFS♦ Exciton and Biexciton Coherent Effects in Quantum Dots
♦ InGaN Cavity Polaritons♦ Fabrication and Physics of Low-Loss Photonic Crystal Slab Waveguides♦ All-optical switches based on photonic crystal nanocavities♦ Nanoelectrode lithography

II. Data◆ Second NTT- Basic Research Laboratories School ............................................................................... 49◆ Science Plaza 2005 ................................................................................................................................ 50◆ The 3rd Advisory Board Meeting .......................................................................................................... 51◆ International Conference on Nanoelectronics, Nanostructures and Carrier Interactions....................... 52◆ Award Winner’s List .............................................................................................................................. 53◆In-house Award Winner’s List................................................................................................................ 55◆List of Visitor’s Talks ............................................................................................................................. 57◆Research Papers, Presentations at International Conferences and Patents ............................................. 61◆List of Invited Talks at International Conferences ................................................................................. 63◆List of Research Papers Published in International Journals.................................................................. 70

Cover photograph:
Compound semiconductor micro/nanomechanical structures
Scanning electron microscope images of various kinds of micro/nanomechanical structures fabricated fromcompound semiconductor heterostructures. The thickness and length of these suspended beams andcantilevers are varying from 20 to 700 nm and from 500 nm to 200 µm, respectively. These structures arecharacterized for studying quantum effects in the coupling of electrical and mechanical degrees of freedom,
and applicable for highly sensitive force and displacement detection. (Page 32)

Member List
As of March 31, 2005(*/ left NTT BRL in the middle of the year)

NTT Basic Research Laboratories
Director, Dr. Hideaki Takayanagi

Research Planning Section

Senior Research Scientist, Supervisor,

Dr. Itaru Yokohama

Senior Research Scientist, Supervisor,

Dr. Akira Fujiwara

Senior Research Scientist,

Dr. Tadashi Nishikawa

Senior Research Scientist,

Dr. Yuichi Harada

NTT R&D Fellow
Prof. Yoshihisa Yamamoto(Stanford University, U.S.A)
Dr. Hideaki Takayanagi(Director, Bacic Research Laboratories)

NTT Research Professor
Prof. Nobuyuki Imoto(Osaka University)
Prof. Masahito Ueda
(Tokyo Institute of Technology)
Prof. Fujio Shimizu(The University of Electro-Communications)
Prof. Yoshihisa Yamamoto(Stanford University, U.S.A)-1-

Materials Science Laboratory

Executive Manager,

Dr. Keiichi Torimitsu
Dr. Hisashi Sato
Dr. Katsuhiro Ajito

Thin-Film Materials Research Group:
Dr. Toshiki Makimoto (Group Leader)
Dr. Makoto Kasu
Dr. Takashi Matsuoka*
Dr. Hideki Yamamoto
Dr. Hiroyuki Shibata
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Dr. Yoshitaka Taniyasu
Dr. Jose Kurian*Dr. Haitao Ye
Low-Dimensional Nanomaterials Research Group:
Dr. Yoshihiro Kobayashi (Group Leader)
Dr. Fumihiko Maeda
Hiroki Hibino
Dr. Prabhakaran Kuniyil
Dr. Hiroo Omi
Dr. Kenichi Kanzaki
Akio Tokura
Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Keisuke Ebata
Dr. Kazuaki Furukawa
Dr. Nahoko Kasai
Dr. Akiyoshi Shimada
Dr. Hiroshi Nakashima
Touichiro Goto
Dr. Mimei Kobayashi
Dr. Tobias Nyberg-2-

Dr. Yasuyuki Kobayashi
Dr. Shin-ichi Karimoto
Dr. Kenji Ueda
Dr. Akio Tsukada

Dr. Kawamura Tomoaki
Dr. Satoru Suzuki
Dr. Jeong Goo-Hwan

Dr. Koji Sumitomo
Dr. Yoshiaki Kashimura
Dr. Chunxi Han

Physical Science Laboratory

Executive Manager,

Dr. Yoshiro Hirayama
Dr. Hiroyuki Tamura
Takeshi Karasawa

Nanodevices Research Group:
Dr. Hiroshi Inokawa (Group Leader)
Dr. Masashi Uematsu
Dr. Yukinori Ono
Dr. Katsuhiko Nishiguchi
Dr. Nicolas Clement
Nanostructure Technology Research Group:
Dr. Hideo Namatsu (Group Leader)Dr. Hiroshi Yamaguchi
Dr. Masao Nagase
Toru Yamaguchi
Junzo Hayashi
Dr. Lionel Houlet*
Quantum Solid State Physics Research Group:
Dr. Yoshiro Hirayama (Group Leader)
Dr. Toshimasa Fujisawa
Dr. Koji Muraki
Dr. Satoshi Sasaki
Dr. Akihito Taguchi
Dr. Toshiaki Hayashi
Dr. Norio Kumada
Dr. Kei Takashina
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Tetsuya Mukai
Dr. Shiro Saito
Dr. Taro Eichler
Spintronics Research Group:
Dr. Junsaku Nitta (Group Leader)
Dr. Tatsushi Akazaki
Dr. Yuichi Harada
Dr. Masumi Yamaguchi
Toshiyuki Kobayashi
Dr. Yuan-Liang Zhong-3-

Dr. Hiroyuki Kageshima
Dr. Kazuyuki Uchida

Dr. Kenji Yamazaki
Dr. Hajime Okamoto

Dr. Kiyoshi Kanisawa
Dr. Kyoichi Suzuki
Dr. Go Yusa

Hirotaka Tanaka
Dr. Alexander Kasper

Dr. Yoshiaki Sekine
Dr. Yiping Lin*

Optical Science Laboratory

Executive Manager,

Dr. Masao Morita
Dr. Masaie Fujino
Dr. Makoto Yamashita

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kyou Inoue
Kazuhiro Igeta
Dr. Hiroki Takesue
Dr. Fumiaki Morikoshi
Dr. Akira Kawaguchi
Quantum Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Hidehiko Kamada
Dr. Hideki Gotou
Dr. Takehiko Tawara
Katsuya Oguri
Dr. Takeshi Kutsuwa
Dr. Stephen Hughes
Dr. Nicholas Cade
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Atsushi Yokoo
Dr. Ryuzi Yano*
Dr. Hideaki Taniyama
Dr. Akihiko Shinya
Dr. Satoshi Mitsugi
Dr. Tetsu Ito-4-

Masami Kumagai
Toshimori Honjo

Dr. Kouta Tateno
Dr. Atsushi Ishizawa
Dr. Yasuaki Okano

Dr.Eiichi Kuramochi
Dr. Takasumi Tanabe

Distinguished Technical Member

Toshiki Makimoto was born in Tokyo on January 16, 1960. He received the B.E., M.S. and
Ph.D. degrees in electrical engineering from the University of Tokyo in 1983, 1985 and 1993,
respectively. He joined NTT Basic Research Laboratories in 1985. He was a visiting
researcher in University of California, Santa Barbara, USA during 1993-1994. Since 1985, he
has engaged in epitaxial growth of III-V compound semiconductors, in-situ monitoring of
epitaxial growth, heterojunction bipolar transistors, and so on. His current interests are
epitaxial growth of nitride semiconductors and its application to devices. He is a member oftechnology evaluation committee for the New Energy and Industrial Technology
Development Organization (NEDO) and the Diamond Research Center in the National
Institute of Advanced Industrial Science and Technology (AIST). He is an associate editor ofJapan Society Applied Physics International and a member of the Japan Society of Applied
Physics, and the Institute of Electronics, Information and Communication Engineers.

Distinguished Technical Member

Hiroshi Yamaguchi was born in Osaka on October 30, 1961. He received the B.E., M.S. inphysics and Ph.D. degrees in engineering from the Osaka University in 1984, 1986 and 1993,
respectively. He joined NTT Basic Research Laboratories in 1986. He was a visiting research
fellow in Imperial College, University of London, UK during 1995-1996. Since 1986 he has
engaged in the study of compound semiconductor surfaces prepared by molecular beam
epitaxy mainly using electron diffraction and scanning tunneling microscopy. His current
interests are mechanical and elastic properties of semiconductor low dimensional structures.
He is a research coordinator of NEDO international joint research project (Nano-elasticity)during 2001-2004 and a member of the Japan Society of Applied Physics and the PhysicalSociety of Japan. He was awarded the paper awards of the Japanese Society of Applied
Physics in 1989 and 2004.
-5-

Distinguished Technical Member

Toshimasa Fujisawa was born in Tokyo on May 23, 1963. He received the B.E., M.S. and
Ph.D. degrees in electrical engineering from Tokyo Institute of Technology in 1986, 1988 and1991, respectively. He joined NTT Basic Research Laboratories in 1991. He was a guest
scientist in Delft University of Technology, Delft, the Netherlands during 1997-1998. Since
2003, he is also a guest associate professor at Tokyo Institute of Technology. Since 1991 hehas engaged in the study of semiconductor fine structures fabricated by focused-ion-beamtechnique and electron-beam lithography technique, transport characteristics ofsemiconductor quantum dot. His current interests are single-electron dynamics in quantum
dots, and their application to quantum information technologies. He received Sir Martin Wood
Prize in 2003 and JSPS (Japan Society for the Promotion of Science) Award in 2005. He is amember of the Japan Society of Applied Physics, and the Physical Society of Japan.

Distinguished Technical Member

Masaya Notomi was born in Kumamoto, Japan, on 16 February 1964. He received his B.E.,
M.E. and Dr. Eng. degrees in applied physics from University of Tokyo, Tokyo, Japan in 1986,
1988, and 1997, respectively. In 1988, he joined Nippon Telegraph and Telephone
Corporation, NTT Optoelectronics Laboratories, Atsugi, Japan. Since then, his researchinterest has been to control the optical properties of materials and devices by using artificial
nanostructures, and engaged in research on semiconductor quantum wires/dots and photonic
crystal structures. He has been in NTT Basic Research Laboratories since 1999, and iscurrently working on light-propagation control by use of various types of photonic crystals.
From 1996-1997, he was with Linköping University in Sweden as a visiting researcher. He is
also a guest associate professor of Tokyo Institute of Technology (2003- ). He is a member of
the Japan Society of Applied Physics, and the American Physical Society.
-6-Advisory Board (2004 Fiscal Year)
Name

Title
Affiliation

Dr. Boris L. Altshuler

Professor
Department of Physics
Princeton University, U.S.A

Dr. Michel H. Devoret

Professor
Department of Applied Physics
Yale University, U.S.A

Dr. Serge Haroche

Professor
Department de Physique
De l’Ecole Normale Superieure, France

Dr. Mats Jonson

Professor
Department of Applied Physics
Chalmers University of Technology, Sweden

Dr. Anthony J. Leggett

Professor
Department of Physics
University of Illinois at Urbana-Champaign
U.S.A

Dr. Johan E. Mooij

Professor
Department of Applied Physics
Delft University of Technology, The Netherlands

Dr. Klaus H. Ploog

Director
Paul-Drude-Institut für Festkörperelektronik
Germany

Dr. John F. Ryan

Professor
Clarendon Laboratory
University of Oxford, U.K

Dr. Klaus von Klitzing

Professor
Max-Planck-Institut für Festkörperforschung
Germany-7-

Invited / Guest Scientists(2004 Fiscal Year)

Name

Affiliation
PeriodDr. Hiroshi Yaguchi

Kyoto University, Japan
December 03 – December 05

Dr. Tobias Nyberg

University of Tokyo, Japan
January 04 – December 04

Dr. Jan Johansson

Japan Science and Technology Agency (JST), Japan
February 04 – January 06

Prof. Tord Claeson

Chalmers University of Technology, Sweden
February 04 – April 04

Prof. C.J.P.M. Harmans

Delft University of Technology, The Netherlands
April 04 – June 04

Dr. Tobias Bergsten

Japan Science and Technology Agency (JST), Japan
April 04 – March 06

Dr. Wakako Suhara

University of Tokyo, Japan
June 04 – March 05

Prof. Yshai Avishai

Ben Gurion University, Israel
August 04 – September 04

Dr. Victor Prinz

Russian Academy of Science, Russia
October 04 – December 04

Dr. Andrei Zaikin

Forschungszentrum Karlsruhe, INT, Germany
October 04 – November 04

Prof. Andreas Knorr

Technische Universität Berlin, Germany
November 04

Prof. Alexander Khaetskii

Ludwig-Maximilians-Universität, Germany
February 05

Dr. Michael Thorwart

Heinrich-Heine-Universität Düsseldorf, Germany
February 05 – March 05-8-

Trainees
Name(2004 Fiscal Year)

Affiliation
PeriodFrank Deppe

Technische Universität München, Germany
May 02 – May 05

Jeff Liu

Simon Fraser University, Canada
June 03 – April 04

Joyce Yat-Ling Wong

University of Toronto, Canada
July 03 – June 04

Guk-Hyun Kim

KAIST (Korea Advanced Institute of Science andTechnology), Korea
Augut 03 – July 04

Nicolas Thillosen

Aachen University of Technology (RWTH) / ResearchCenter Jülich, Germany
November 03 – April 04

Christopher Schierholz

Universität Hamburg, Germany
January 04 – July 04

Julien Duvernay

INSA (Institut National des Sciences Appliquées), France
February 04 – September 04

David Deen

University of Oklahoma, U.S.A.
May 04 – August 04

Kislon Voitchovsky

University of Oxford, U.K.
June 04

Michael Wagenknecht

Universität Tübingen, Germany
June 04 – December 04

Aravind Vijayaraghavan

Rensselaer Polytechnic Institute, U.S.A.
June 04 – December 04-9-Christopher Margach

University of Glasgow, U.K.
July 04 – January 05

Marc-Aurèle BrunESPCI (École Supérieure de Physique et de Chimie
Industrielles), France
July 04 – December 04

Olivier Crauste

ESPCI (École Supérieure de Physique et de Chimie
Industrielles), France
July 04 – December 04

Kasper Grove-Rasmussen

University of Copenhagen, Denmark
August 04 – December 04

Simon Perraud

University of Paris 6 / CNRS, France
October 04 – September 05

Eek Huisman

University of Groningen, The Netherlands
November 04 – March 05

Huang-Ming Lee

National Chiao Tung University, Taiwan R.O.C.
November 04 – November 05

Yueh-Chin Lin

National Chiao Tung University, Taiwan R.O.C.
November 04 – May 05

Arnaud Valeille

SUPAERO (École Nationale Supérieure de L’aéronautiqueet de L’espace), France
January 05 – August 05

Wouter Naber

Delft University of Technology, The Netherlands
January 05 – June 05

Francois Chabrol

University of Newcastle Upon Tyne, U.K.
February 05 – March 05

Shih-Chieh Huang

National Chiao Tung University, Taiwan R.O.C.
February 05 – February 06- 10 -

Vittorio PeanoHeinrich-Heine-Universität Düsseldorf, Germany
February 05 – March 05

Taryl Leaton Kirk

Universität Stuttgart, Germany/ Max-Planck-Institut für Festkörperforschung, Germany
March 05 – April 05- 11 -

Japanese Students(2004 Fiscal Year)

Name

Affiliation (Period)

Yuichi Igarashi

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Yasuaki Iwai

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Kuniaki Endo

Tokyo University of Science, Japan (May 04 – Mar. 05)

Keji Ohno

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Satoru Ohno

Keio University, Japan (Mar. 05)

Junya Ono

University of Tsukuba, Japan (Mar. 05)

Akichika Karasawa

Shonan Institute of Technology, Japan (Jun. 04 – Mar. 05)

Hiroshi Kanda

Tokyo Institute of Technology, Japan (Jul. 04-Aug. 04)

Koya Kitagawa

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Yosuke Kitamura

University of Tokyo, Japan (Jan. 05 – Mar. 05)

Takatoshi Kido

Shonan Institute of Technology, Japan (Apr. 04 – Mar. 05)

Go KiraTokyo Institute of Technology, Japan (Apr. 04 – Mar. 05)

Tatsuya Kutsuzawa

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Tetsuo Kodera

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Naofumi Kobayashi

Meiji University, Japan (Apr. 04 – Mar. 05)

Shingo Kondo

Tokai University, Japan (Apr. 04 – Mar. 05)

Daisuke Sato

University of Tsukuba, Japan (Apr. 04 – Mar. 05)

Takuya Shigetomi

Kumamoto University (Jul. 04 – Aug. 04)

Jun Sugawa

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Atsushi Sogabe

Shonan Institute of Technology, Japan (May 04 – Mar. 05)

Akio Takahashi

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Kazuyuki Tamura

Nagaoka University of Technology (Oct. 04 – Feb. 05)

Masaru Tsuchiya

Keio University, Japan (Apr. 04 – Mar. 05)- 12 -

Katsuhiko Degawa

Tohoku University, Japan (Jan. 05 – Mar. 05)

Ritsuya Tomita

Tokyo Institute of Technology, Japan (Apr. 04 – Mar. 05)

Hiromasa Nakano

Tokyo University of Science, Japan (Aug. 04 – Mar. 05)

Tomohiro Nakamura

Shonan Institute of Technology, Japan (May 04 – Mar. 05)

Yoshifumi Nishi

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Masumi Noda

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Kenichi Hidachi

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Shigeto Fukatsu

Keio University, Japan (Apr. 04 – Mar. 05)

Yusuke Furukawa

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Munekazu Horikoshi

The University of Electro-Communications, Japan(Apr. 04 – Mar. 05)

Motonari Honda

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Tetsunori Matsumoto

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Kenji Miyakoshi

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Takuya Mouri

Tokyo University of Science, Japan (Apr. 04 – Mar. 05)

Masakazu Morita

Tokyo Institute of Technology, Japan (Apr. 04 – Mar. 05)

Shin Yabuuchi

Keio University, Japan (Apr. 04 – Mar. 05)

Michihisa Yamamoto

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Tomoo Yokoyama

Yokohama National University, Japan (Apr. 04 – Mar. 05)

Hiroyasu Yokoyama

University of Tokyo, Japan (Apr. 04 – Mar. 05)

Hideto Yoshida

Osaka University, Japan (Nov. 04 – Dec. 04)- 13 -

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Overview of Research in Laboratories
Material Science Laboratory
Keiichi Torimitsu
The Materials Science Laboratory (MSL) aims at producing new functional materials anddesigning of advanced device based on novel materials and biological function. Controllingthe configuration and coupling of atoms and molecules is our approach to accomplish thesegoals. Bio-nano research is set as our principle research in this laboratory.
We have three research groups covering from inorganic materials, such as semiconductors,
to organic materials, such as neurotransmitters. The characteristic feature of MSL is theeffective sharing of the unique nanofabrication and measurement techniques of each group.
This enables fusion of research fields and techniques, which leads to innovative material
research for the IT society.
We set up European laboratory in UK for bio-nano research, our principal research, in
October and started collaboration with University of Oxford.
Physical Science Laboratory
Yoshiro Hirayama
We are studying solid-state quantum systems and nanodevices, which will have
revolutionary impact on communication and information technologies in the 21st century. In
particular, we are making firm and steady progress in the pursuit for solid-state qubits, andrelated physics and technology for future quantum information processing. We maintain an
open-door policy and engage in collaborations with many outside organizations to enhance
our basic research into fundamental issues.
The five groups in our laboratory are working in the following areas: quantum coherent
control of semiconductor and superconductor systems, carrier interactions in semiconductor
hetero- and nanostructures, spintronics manipulating both electron and nuclear spins, precise
and dynamical control of single electrons, nanodevices operating at ultimately low power
consumption, atom traps/optics, and novel nanomechanics based on compound
semiconductors. These studies are supported by cutting-edge nanolithography techniques,
well-controlled nanofabrication processes, high-quality crystal growth, and theoretical studies
including first-principle calculations.
Optical Science Laboratory
Masao Morita
This laboratory started April 2004, and aims the development of core-technologies thatwill innovate on optical communications and optical signal processing, and seek fundamental
scientific progress.
The three groups in our laboratory are working for the quantum state control of light, thequantum state control of materials using light, the analysis of high speed phenomena using
very short pulse laser, the optical properties of nano-structure semiconductor like quantum
dot, very small optical integrated circuit, and so on.
In this year, we realized the high speed and long distance quantum cryptography, thepolariton laser based on nitride semiconductor, and the optical bistable switch composed ofhigh Q-value photonic crystal resonator.

- 15 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Fabrication of Josephson junctions using MgB2
Kenji Ueda, and Toshiki Makimoto
Materials Science Laboratory
The superconducting transition temperature （Tc） of magnesium diboride (MgB2) is39K, the highest among metallic compounds [1]. The mechanism of superconductivity of
MgB2 has been determined to be multi-gap superconductivity, and much research on MgB2 isinvestigating superconducting electronic applications.
Superconducting tunnel junctions (Josephson tunnel junctions) are the key components
of devices for superconducting electronic applications such as high-sensitive magnetic
sensors (SQUID) and electromagnetic wave detectors. Nb（Tc=9K） tunnel junctions aremainly used in these superconducting devices, but cooling down devices using Nb requires
liquid helium. MgB2, on the other hand, has higher Tc and superconducting devices using
MgB2 tunnel junctions can work without using liquid helium. There have been many
attempts to fabricate Josephson tunnel junctions that work above liquid nitrogen temperature(77 K) using high-Tc superconductors (HTS). However, Josephson tunnel junctions using
HTS have not been fabricated yet, although it has been almost twenty years since thediscovery of HTS. Therefore, MgB2 is expected for materials fabricating Josephson tunnel
junctions.
We have succeeded in fabricating Josephson tunnel junctions (MgB2/AlOx/MgB2) using
as-grown MgB2 films fabricated by molecular beam epitaxy (MBE) [2] and observed, for the
first time, supercurrent at 20 K [3]. This temperature is the highest among artificiallyfabricated tunnel junctions and can be easily reached by using compact commercial
cryocoolers.
Even though the properties of our tunnel junctions still have to be improved further, we
believe that these results will enlarge the area of the superconducting electronic applications.
[1] J. Nagamatsu et al., Nature 410 (2000) 63.
[2] K. Ueda, M. Naito, Appl. Phys. Lett. 79 (2001) 2046.
[3] K. Ueda, S. Saito, K. Semba, T. Makimoto, and M. Naito, Appl. Phys. Lett. 86 (2005)
172502.

Fig. 1： Typical current-voltage characteristicsof the MgB2 tunnel junction measured
at 4.2 K.

- 16 -

Fig. 2： Temperature dependence ofsupercurrent of the MgB2 tunnel
junction. The inset shows currentvoltage characteristics measured at
20K.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

InGaN quantum wells with high luminescent efficiency
Tetsuya Akasaka, Hideki Gotoh, Hidetoshi Nakano, and Toshiki Makimoto
Materials Science Laboratory

300

50

T (K)
25

2.5

17

PL ηRT: 71% (highest value)

Lifetime, τPL (ns)Integrated PL intensity (arb. units)

InGaN quantum wells (QWs) have been widely used as the active layers of light emitting
diodes and laser diodes that emit light in the visible-to-ultraviolet region. Nevertheless, theperformance of these devices has been limited, in part by the emission efficiency of InGaN
QWs. The emission efficiency of InGaN QWs is governed by various factors, such as
spatial fluctuation of the InN composition and nonradiative recombination centers (NRCs).
In this study, InGaN QWs were grown on InGaN under-lying layers (ULs) which function to
reduce the NRCs and spatial fluctuation of the InN composition. These InGaN QWs on
InGaN ULs have the highest luminescent efficiency at room temperature (RT) ever reported[1, 2]. Time-resolved photoluminescence (TRPL) revealed that adding indium atoms to the
UL is effective in eliminating the NRCs of InGaN QWs.
Figure 1 shows Arrhenius plots of integrated PL intensity for InGaN QWs on an InGaNUL. The integrated PL intensity remains almost constant at 14-150 K and then falls
gradually with a further increase of temperature. Even at RT, however, it is 71 % of that at
14 K. This value is the highest ever reported for the wavelength region of about 400 nm.
PL lifetimes measured by TRPL, τPL, are plotted as a function of temperature in Fig. 2. The
τPL values for a conventional InGaN QWs rapidly decrease with increasing temperature
because of the thermally activated NRCs. For the InGaN UL, τPL values stay almost
constant at 0.9 ns below 100 K, reflecting the behavior of localized excitons. This meansthat the tail states originated from the fluctuation of the InN composition is fairly shallow.
From 100 to 250 K, τPL linearly increases with temperature, which is characteristic of 2Dexcitons in QWs. This linear increase in τPL was clearly observed up to 250 K because of
fewer NRCs. These results indicate that the InGaN UL can effectively eliminate the NRCs
and also decrease the spatial fluctuation of the InN composition.
InGaN QWs on an InGaN UL are very promising for realizing novel optoelectronic
devices, such as polariton lasers and single photon emitters, which require extremely highluminescent efficiency at RT.
[1] T. Akasaka et al., Appl. Phys. Lett. 85 (2004) 3089-3091.
[2] T. Akasaka et al., Appl. Phys. Lett. (accepted).

100

10

1
0

NTT new structures(InGaN UL)

2.0
1.5
1.0
0.5
0.0

20

40
60
1000/T (K-1)

80

InGaN UL

Conventional
0

100

200

300

T(K)

Fig. 1. Arrhenius plots of integrated PL
intensity for InGaN QWs on an InGaN UL

Fig. 2. Temperature dependence of PL
lifetime, τPL- 17 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

An InGaN-based horizontal cavity surface emitting laser diodeTetsuya Akasaka, Toshio Nishida, Naoki Kobayashi, and Toshiki Makimoto
Materials Science Laboratory
Group III-nitrides, such as AlN, GaN, InN, and their alloys, are attractive for application
to optoelectronic devices in the visible and UV ranges, because these semiconductors havewide and direct bandgaps. The mirror facets of group III-nitride-based lasers have been
fabricated by either cleaving or dry-etching. Selectively grown microfacets are better
choices for fabricating mirror facets. In this work, we fabricated an InGaN-based horizontal
cavity surface emitting laser diode (HCSELD) [1]. It is a Fabry-Perot laser diode that has apair of cavity mirrors consisting of selectively grown vertical {11-20} microfacets and a pairof outer micromirrors consisting of the selectively grown inclined {11-22} microfacets. The
outer micromirrors direct the laser beam upward. Successful room-temperature lasing of the
InGaN-based HCSELDs has been achieved by current injection.
Figure 1 shows an SEM bird’s-eye-view photograph of an InGaN-based HCSELD. It
can be seen that a Fabry-Perot cavity mirror and an outer micromirror are a vertical {11-20}
microfacet and an inclined {11-22} microfacet of the regrown Mg-doped GaN layers,respectively. The {11-20} Fabry-Perot cavity mirror of the HCSELD is vertical to a SiC
substrate. The angle between the inclined {11-22} outer micromirror and the SiC substratesurface is 58 degrees. Therefore, geometrically, laser beams are emitted at an angle of 64
degrees to the substrate surface. The InGaN-based HCSELDs lase at room temperature(RT) by current injection. Spectra obtained below and above the lasing threshold are shownin Fig. 2. The narrowing of the spectrum can be seen at current density above the lasing
threshold. The lasing wavelength is approximately 400 nm. We also observed thenonlinear change in the current-light output relationship at the lasing threshold. This is thefirst current-injection lasing of the nitride-based surface emitting laser diode.
[1] T. Akasaka et al., Appl. Phys. Lett. 84 (2004) 4104-4106.

Pused@RT
0.3µs, 1kHz
Intensity (arb. units)Outer mirror{11-22} microfacetPelectrode

Lasingspectrum

I=1.01Ith

I=0.97Ith
5µm

340

Cavity mirror{11-20} microfacet
Fig. 1. Bird’s-eye-view SEM photograph of
an InGaN-based HCSELD.

380
420
Wavelength (nm)460

Fig. 2. Emission spectra obtained from an
InGaN-based HCSELD below and above
the lasing threshold.
- 18 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Growth of High-Quality GaN Using Novel Buffer Layer
Kazuhide Kumakura, *Masanobu Hiroki, and Toshiki Makimoto
Materials Science Laboratory, *NTT Photonics Laboratories
The quality of a GaN layer grown on sapphire substrates by metalorganic vapor phase
epitaxy (MOVPE) has been improved by the use of low-temperature AlN or GaN buffer
layers. Since the low-temperature deposited layer is unstable, it is well-known that variously
shaped islands were formed as temperature increased. Therefore, it is difficult to grow the
GaN layer with sufficient quality or reproducibility, which is a quite severe problem from thecommercial point of view. Thus, it is important to find a new buffer layer for GaN growth on
sapphire substrates.
Electron cyclotron resonance (ECR) plasma sputtering can easily deposit a minute,uniform, and stable oxide or nitride layer on large area at room temperature. An Al2O3 and an
AlN can also be easily deposited by ECR plasma sputtering at room temperature, and havevery high melting points above 2000 °C, indicating that these materials could be used as abuffer layer with good thermal stability. Therefore, we have proposed and demonstrated the
GaN growth on sapphire substrates with the ECR plasma sputtered layer of Al2O3/gradedAlON/AlN/Al2O3 as a buffer layer instead of low-temperature AlN or GaN layer.
We formed the buffer layers on c-face sapphire substrates by ECR plasma sputtering atroom temperature and used them as the growth substrates. The total thickness of the buffer
layers was 20 nm. We directly grew GaN on these substrates at 1000 °C. Figures 1 (a) and (b)show the energy dispersion x-ray spectroscopy (EDS) profiles and the cross-sectionaltransmission electron microscope (TEM) image at the interface between the sapphire
substrate and the GaN layer, respectively. The peak intensities from nitrogen (N) increased
gradually from the sapphire substrate to GaN layer, and those from oxygen (O) decreased
gradually, as shown in Fig. 1 (a). These results indicate that we can easily form the nitride
layer by gradually changing the composition from the oxide layer.
The cross-sectional bright-field TEM image showed that the dislocations were bended at
the initial stage of the growth as shown in Fig. 2, which indicated the enhancement of thelateral growth, resulting in the decrease of dislocation density to be 6.0 × 108 cm-2 in the GaN
layer. The mobility of the GaN layer was 540 cm2/V·s at the electron concentration of 2 ×
1017 cm-3. These results indicate that the quality of the GaN layer grown using the ECR
plasma sputtered buffer was comparable or superior to the conventional grown GaN using the
low temperature buffer layer.
Ga

(a)

(b)
GaN

Intensity [a.u.]

Al
N

6

O

6

5

5

buffer4

2

2

sapphire

1

0.5

1

1.5

4
3

3

0

GaN

1

sapphire sub.

50nm

2

Energy [keV]

Figs. 1. (a) The EDS profiles and (b) the crosssectional TEM image at the interface between
the sapphire substrate and the GaN layer,
respectively.
- 19 -

Fig. 2. Cross-sectional TEM image ofthe interface between the sapphire
substrate and GaN layer.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

AlN field emission display
Y. Taniyasu, M Kasu, and T. Makimoto
Materials Science Laboratory
Aluminum nitride (AlN) is a wide-band-gap (6.2 eV) semiconductor. Its electron
affinity is nearly zero. Therefore, AlN is a promising material for field emitters because
electrons in materials with nearly zero electron affinity can be easily extracted from thesurface to vacuum. However, for AlN, the reported field emission current is too low and theturn-on electric field too high for device application. The reason is that the electron
concentration in the AlN samples is so low that the electrons necessary for field emission can
not be efficiently supplied to the surface.
Recently, we have achieved n-type conductive Si-doped AlN [1]. In addition, we foundthat heavy Si doping is very effective in improving the field emission properties of AlN [2].
This study demonstrates a triode-type field emission display (FED) and presents the fieldemission properties of the heavily Si-doped AlN in an actual device structure [3].
The display has a vertical triode structure consisting of the heavily Si-doped AlN cathode,mesh grid, and phosphor coated anode screen as shown in Fig. 1. The electrons are emitted
by applying grid voltage and then accelerated by the anode voltage. The phosphor is excitedby the electrons and emits luminescence. The cathode current (field emission current), IC,
was detected at an electric field strength of EG = 11 V/µm. Above this turn-on electric field,
the IC increased exponentially with increasing electric field strength and reached 16 µA at EG= 23 V/µm. We measured the stability of the cathode current against time under the DC
mode without a feedback circuit. The display showed a low current fluctuation of 5.5 %.
The high stability originates from the strong Al-N bond strength.
Figure 2 shows photographs of the display during operation. The luminescence area isalmost the same as the opening area of the mesh grid. We observed uniform luminescencewith the brightness of 300 cd/m2, which is intense enough for display application. During
operation, the uniform and bright luminescence was maintained over the entire field emission
area. These results prove that the heavily Si-doped AlN field emitter is very promising for
vacuum microelectronic devices.
[1] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 85 (2004) 4672.
[2] M. Kasu and N. Kobayashi, Appl. Phys. Lett. 79 (2001) 3642.
[3] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 84 (2004) 2115.

Fig. 1. Schematic diagram of display structureusing heavily Si–doped AlN.
- 20 -

Fig. 2. The photograph of the display
during operation.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Real-time Observation of Nanowire Formation by Means of GISAXS
Tomoaki Kawamura, Satyaban Bhunia, *Seiji Fujikawa and Yoshio Watanabe
Material Science Laboratory, *University of Hyogo
Nanowires composed of several semiconductor materials have recently been attracting
many interests due to their promising potential for nano-technology applications such as
photonics, quantum computing and bio / medical engineering. Several nanowires have beengrown using the vapor-liquid-solid (VLS) mechanism in a gaseous environment andevaluated after the growth, using electron-based microscopic techniques, such as SEM andTEM. Since electron-based techniques are limited in vacuum, usual monitoring tool, forexample, RHEED and LEED can not be applied to observe nanowire growth, and details of
the growth is still unclear. In contrast with the electrons, x-ray has larger permeability withthe materials, and is often used for monitoring crystal growth in solid, liquid and gases.
In this work, we evaluated nanowire growth with using GISAXS (Grazing Incidence Small
Angle X-ray Scattering) since this technique can be applied fro evaluating nano-structures ina gaseous and liquid environment. Figure 1 shows the experimental layout for GISAXS
measurement. X-rays were impinged at the grazing condition and scatterings from thenanowires were observed with the digital x-ray CCD camera every several seconds. Figure 2
shows the GISAXS image obtained just after the nanowire growth. Obviously, clear
scatterings along qy and qz direction were observed, suggesting dense nanowires on thesubstrate. Theoretical calculations with using DWBA (Distorted Wave Born Approximation),shown in Fig. 3 (a) and (b), suggests x-rays were scattered mainly by the hexagonal objects
than hemispheres. This was consistent with the results of SEM observation which clearly
showed vertical nanowires with hexagonal cross-section.
[1] T. Kawamura, et al., Proc. of XTOP 2004, Prague, September 2004.
[2] S. Bhunia, et al., Appl. Phys. Lett. 83 (2003) 3371.
qz
N a n o w ire

(a)

qz
qy

qy

X ‑ra ysX ‑ra y C C D ca m e ra

Fig.1 Experimental layout of GISAXS.
(b)

qz

qz
qy

qy

Fig.3 Calculated GISAXS image by
DWBA approximation. (a)hemisphere, (b) hexagonal pillar.

Fig.2 GISAXS image after nanowires
formation (Ts=400℃)- 21 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Synthesis of Functionalized Carbon Nanotubes
using DNA and Gold Nanoparticles
Goo-Hwan Jeong, Satoru Suzuki and Yoshihiro Kobayashi
Material Science Laboratory
Due to the outstanding physical, chemical and electrical properties of carbon nanotubes(CNT), a number of applications in various fields are expected. Especially, extensive
researches related with CNT-functionalization using foreign atom or molecules have been
performed to control electronic property of CNT because diameter- or chirality-controlled
growth has not been realized yet, which is determining factor of electronic property. Here, we
introduce our CNT-functionalization study for the application of CNT-based nanoelectronics
or biosensor. DNA and Au nanoparticles (NP) are selected among various materials tofunctionalize CNT [1] owing to their specific assembling and strong coupling properties.
Ferritin covered with protein shell and contains Fe clusters in its 6-nm diameter innerspace was used to synthesize diameter-controlled single-walled carbon nanotubes (SWNTs).
A Co-ferritin, Fe is replaced by Co, was also used. By controlled methane CVD experiments
at 900ºC, suspended SWNTs are successfully synthesized on Si or SiO2 pillar-structured
substrates using not only ferritin but also Co-ferritin, which is the first report [2]. A scanningelectron microscope (SEM) image [Fig. 1(a)] and Raman spectrum [Fig. 1(b)] of thesuspended SWNTs grown using Co-ferritin catalyst are presented.
SWNTs-functionalization was performed by covalent coupling between carboxyl andamine groups produced by acid and aminopropyltriethoxysilane (APTES) treatment,
respectively. DNA/Au hybrids were made by simple mixing of thiolated-DNA and Au NP(5nm diameter). Finally, SWNTs are modified by Au NP or DNA/Au hybrids.
Figure 2 shows SEM images obtained from SWNTs/Au [Fig. 2(a) and (b)] andSWNTs/DNA/Au hybrids [Fig. 2(c)]. The density of Au NP attached along the suspended
SWNTs was controlled by changing treatment time and Au-colloid concentration. In addition,
the change of Raman spectra was also observed from the SWNTs/DNA/Au hybrid [3], which
implies the different electronic or optical properties are expected. These results show
functionalized CNT can be developed to electronic and optical applications.
[1] M. Zheng et al., Science 302 (2003) 1545-1548.
[2] G.-H. Jeong et al., J. Am. Chem. Soc., submitted 2005.
[3] G.-H. Jeong et al., MRS 2005 Spring Meeting, San Francisco, March 2005.

Fig. 1. Suspended SWNTs from Co-ferritin.
(a) SEM image and (b) Raman result.

Fig. 2. SEM images of CNT/Au hybrids [(a),(b)]and CNT/DNA/Au hybrid (c).
- 22 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Spatially Selective Removal of Carbon Nanotubes
Satoru Suzuki, and Yoshihiro Kobayashi
Materials Science Laboratory
Carbon nanotubes are one of the most promising materials for future nanoelectronics,
because of the nanometer-scale structure and the unique electronic properties. Actually, ananotube-based field effect transistor and single electron transistor have been demonstrated toovercome a Si device. For fabricating a nanotube-based integrated circuit, it is necessary toplace nanotubes only at specified positions. However, high-density nanotube growth almost
always results in the growth of unnecessary nanotubes at unspecified positions, which would
cause short circuits, because controlling the growth direction of individual nanotubes is still
impossible. Thus, selective removal of carbon nanotubes from a nanotube network is a crucial
issue for fabricating an integrated circuit.
Recently, we found that low-acceleration-voltage electron irradiation induces significant
damage in single-walled carbon nanotubes (SWNTs). Moreover, we developed a simple
method for removing unnecessary nantoubes selectively utilizing the low-accelerationvoltage electron irradiation damage.
Raman spectra of SWNTs before and after electron beam irradiation is shown in Fig. 1.
The acceleration voltage was 1 kV. The electron irradiation drastically decreased the radial
breathing modes (RBM) intensity, which is characteristic in the quasi-one-dimensional
structure of SWNTs, indicating that the irradiation caused structural damage in the SWNTs[1]. This damage was found to be extensively caused at around 1 kV. Although SWNTs are
chemically highly stable, the electron irradiation significantly reduces the chemical stability.
This enables us to simply remove the damaged SWNTs selectively. A typical example ofsuspended SWNTs after the selective removal procedure is shown in Fig. 2. The SWNTs
were grown on Si pillars having diameters of 200 nm. The electron beam was scanned along
the dashed line, and then, the sample was annealed in air. In spite of the very simple
procedure, the SWNTs initially crossing the line were successfully removed. This techniquewould make it possible to fabricate various kinds of nanotube circuits.
[1] S. Suzuki et al., Jpn. J. Appl. Phys. 43 (2004) L1118.
[2] S. Suzuki et al., Jpn. J. Appl. Phys. 44 (2005) L133.
14x10

3

Intensity (arb. units)

12

unirradiated17-2
5.8x10 cm
18-2
1.2x10 cm

RBM

10
8
6
Si

4
2
0
100

200

300

400
-1

Raman Shift (cm )Fig. 1. Raman spectra of SWNTs before
and after electron irradiation.

Fig. 2. SEM image of the suspended
SWNT network after the selective removal
procedure. The electron beam was scannedalong the dashed line. Scale bar: 2.5 µm.
- 23 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Arrangement of Au-Si alloy islands at atomic steps
Hiroki Hibino and Yoshio Watanabe*
Materials Science Laboratory
Approaches to fabricating semiconductor nanostructures can be roughly classified into
“top-down” lithography and “bottom-up” self-assembly. Self-assembly has potential
advantages of low cost, large scale, high quality, and so on, but there still remain lots ofproblems to be solved, especially in the controllability of the size and position ofnanostructures. Our group has developed novel self-organized nanostructure fabrication
methods through atomic scale control of semiconductor surface structures. Here, we
demonstrate that Au-Si alloy islands are self-assembled in a controlled manner using an
atomic step array on Si(111) as templates.
We formed three-dimensional (3D) islands on Si(111) by Au deposition at high (∼700°C)
and then at low (∼400°C) temperatures. Figure 1 shows an atomic force microscopy (AFM)
image of the islands and their height distribution. 3D islands with a relative deviation of 10%
are arranged at atomic steps. Real-time observations of the island formation using low-energy
electron microscopy (LEEM) revealed that the islands formed within a narrow Au coveragewindow, resulting in the narrow size distribution. The islands were allowed to coarsen byinterrupting the Au deposition. When the Au deposition was resumed, the islands moved into
upper terraces leaving trenches behind. This indicates that the islands are Au-Si alloy droplets.
Additionally, the islands moved on the terraces almost at constant velocities, but when they
approached the upper-side steps, they jumped to the steps (Fig. 2). The atomic steps provide
stable positions for Au-Si alloy islands, which helps them to arrange at the steps.
We showed that the position and size of Au-Si alloy islands can be controlled by using
atomic steps as templates for island formation. Our method is very simple because it does notinclude any lithographic techniques, and it is useful for preparing substrates forsemiconductor nanowire growth and attaching functional molecules.
*
Present address: NTT advanced technology Corporation

Fig. 1. AFM image of 3D islands and theirheight distribution.

Fig. 2. The moving distance of the island
indicated by the dotted circle in LEEM
images (a)-(c) as a function of time.
- 24 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Development of a conducting polymer electrodeand measurements of neural activity with a microelectrode array
Akiyoshi Shimada, Tobias Nyberg, Nahoko Kasai and Keiichi Torimitsu
Materials Science Laboratory
The brain processes information related to perception, consciousness and behavior byusing two types of electrical signals: localized graded potentials and action potentials.
However, it is less well understood how information is coded by these electrical signals or
how neural networks develop.
To answer these questions, we recorded the activity from dissociated cultures of rat or
mouse cerebral cortical neurons with a microelectrode array (MEA). MEA-based recording isan effective way to study the relationship between the electrical activities of individual
neurons and the neural network that they compose.
However, the extracellular signals produced by neurons are generally small. This has led
to the need for a conducting polymer electrode with a low signal-to-noise ratio. Figure 1
shows the structure of a conducting polymer electrode with low impedance. The impedanceof this electrode was about 5 kΩ at 1 kHz [1], which is one-twentieth that of a conventional
platinized electrode [2]. We confirmed that this polymer electrode could measure the action
potentials of cortical neurons for more than 1 month.
In addition, there are two types of neurons (excitatory and inhibitory) in a neural network,
and it is difficult to identify the neuron type in living tissue. So we have employed a recently
developed glutamic acid decarboxylase-green fluorescence protein (GAD67-GFP) knock-in
mouse to allow us to observe the distribution of GABAergic neurons, which constitute themajority of inhibitory neurons, as shown in Fig. 2. Developmental changes in the spontaneous
activity suggested that GABAergic neurons became active earlier than non-GABAergic
neurons.
We are now investigating the interaction between excitatory and inhibitory neurons inrelation to information processing with this polymer electrode.
[1] T. Nyberg et al., Neuro2004 Sept 21-23, Osaka, Japan (2004).
[2] Y. Jimbo et al., IEEE Trans. Biomed. Eng., 50, 2 (2003) 241.

- 25 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

AFM observation of purified IP3 receptor protein
1

Wakako Suhara, 1Ichiro Fujimoto, 1,2Katsuhiko Mikoshiba, 1,3Mime Kobayashi
1,3
Touichiro Goto, and 1,3Keiichi Torimitsu
1
The Division of Neural Signal Information, NTT-IMSUT2The Institute of Medical Science, University of Tokyo, 3Materials Science Laboratory
Mikoshiba’s group identified an abundant glycoprotein that exists in Purkinje cells of
cerebellum as an inositol 1,4,5-trisphosphate receptor (IP3R) in 1989. IP3R has shown toplay pivotal roles in neuronal transmission and other functions that relate to morphologicaland physiological processes in living organisms. Those functions include fertilization,
activation of an egg, axon extension of a neuron, and cerebral nerve plasticity.
Previous analysis of numerous negatively stained images of fixed samples has indicatedthat the receptor changes its morphology depending on intracellular Ca2+ concentrations. The
receptor was square-shape in un-liganded state and windmill-shape in the presence of Ca2+.
In this study, we attempted to observe unfixed samples of a single IP3R protein by atomic
force microscopy (AFM).
The same samples used for the previous electron microscopic studies were used. Single
IP3R tetramers on mica were successfully observed in imaging buffer without detergent (Fig.
1A). The square-like structure with a width of about 25 nm closely resembles the model
proposed in previous studies. We expect that individual IP3R molecules assemble in acertain direction resulting from the electrostatic interaction between IP3R and the mica
surface. After imaging IP3R in standard imaging buffer without Ca2+, buffer was changed tothe one with Ca2+. We found several types of structures in the presence of Ca2+. Most
notably, we found IP3R tetramer with a dent in the center (Fig. 1C). While the heightdecreased slightly, the width clearly increased. The structure resembles the windmill-like
configuration reported in a previous electron microscope study. The IP3R appeared to be
inclining slightly backwards, and twowing-like structures that were higher thanA
B
others could be distinguished. Section
analysis along these two higher structures
showed a width of 30 nm.
We believe that our study is an
25 nm
important
stepping-stone
for
the
3D
Top view
application of AFM to biological samples.
2 nm
Further improvements in AFM will makeit possible to reveal the structural changes
CDof other membrane proteins in a naturalenvironment.
[1] W. Suhara et al., 34th annual meetingof Society for Neuroscience, San Diego,
25 nm
USA (2004)[2] I. Fujimoto et al., 9th Linz winter
3D
Top view
2 nm
workshop, Linz, Austria (2005).
Fig. 1. AFM topographs of IP3R. Single IP3R imaged without (A) or with (C) Ca2+ inbuffer. Section analyses along dotted lines are shown in bottom insets. Threedimensional reconstructed models are shown in (B) and (D).

- 26 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Photoresponse Behavior of Conjugated Polymer-Based Nano Device
Hiroshi Nakashima, Wenping Hu, Kazuaki Furukawa, Yoshiaki Kashimura, Katsuhiro Ajito
and Keiichi Torimitsu
Materials Science Laboratory
Molecular-scale device, comprising single or small number of organic molecules, hasexperienced extensive attention and rapid development recently. Bottom-up process usingorganic molecules enables us to fabricate high-dense and fine-tuned devices due to theadvantages in size and design of the molecules. Conjugated polymers exhibit remarkablecarrier transport and photo absorption/emission properties based on electrically conjugatedpolymer chain, and are thus expected to apply nano-scale electronic and photonic device
components. Recently, we have synthesized a rigid π-conjugated poly(p-phenyleneethynylene) derivative including thiol end groups (TA-PPE, Fig.1) [1]. By utilizing a
selective chemisorption property of thiol end groups onto Au surface, it is possible tofabricate a self-assembled TA-PPE nanojunction between Au nanogap electrodes, Au/TAPPE/Au (gap ~40 nm). We successfully observed a remarkable photocurrent switching
behavior of the nanojunction [2].
Figure 2 shows the photocurrent response behavior of the nanojunction under lightirradiation. With light on or off, the nanojunction exhibits switching between a low-current
state in dark conditions and a high-current state in light conditions as a nanometer-scale
photoswitch (the voltage between two nanoelectrodes is kept constant at 0.5 V). In the “off”
state, the resistance is as high as ~1015 Ω. In the “on” state, the resistance is ~1012 Ω, theswitching ratio is as high as 1000. The switching in those two states is reversible and fast.
Under illumination, the photon-generated excitons are dissociated into free electrons andholes, some of them possessing sufficient energy to jump over or tunnel through the Au-S
barrier, resulting in high current (“on” state) of the nanojunction. In addition, with intensityof the incident light changing, the current of the nanojunction device changed, exhibiting
significant light intensity dependence. This phenomenon is understandable in terms of thechanging of photon density in the incident light.
In the future, we are aiming at the fabrication of novel molecular-scale composite devices
integrating the nanojunction with other optoelectrically functionalized organic/bio molecules.
[1] H. Nakashima, et al., Langmuir 21 (2005) 511.
[2] W. Hu, et al., J. Am. Chem. Soc. 127 (2005) 2804.
hν

4000
4.0

nanogap electrodes (gap: 40 nm)

Au

Current (fA)
Current(pA)

OFF OFF

Au
S

)n

(

SiO2 (300nm)

S

OFF OFF OFF OFF

3000
3.0

2000
2.0

1000
1.0

OC6H13

Si
Z

(

)n

C6H13O
NH4OH

Z

00

Z = SCOCH3
Z’= SH

Dark

Dark

Light ON ON ON ON ON
0

1000

2000

ON

3000

4000

5000

Time (Second)Fig. 1. Molecular structure of TA-PPE andnanodevice structure- 27 -

Fig. 2. Photoresponse characteristics of the
nanojunction device (white light, 52 mW)

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Organotypic culture techniques and study of neural toxicity
Chunxi Han, Nahoko Kasai, and Keiichi Torimitsu
Materials Science Laboratory
Organotypic slice culture technique of rat hippocampus is very important tool to study thephysiological and pharmacological properties of neuron and neuronal circuits. Because theslices retain the cytoarchitecture and neuronal circuits of the tissue and because they are
relatively easy to prepare, it is one of the best materials to study long-term studies of neuronal
network. In epileptic animal models and human temporal lobe epilepsy, many studies havereported that the CA1 and CA3 sectors of the hippocampus are susceptible to neuronal cell
death. However, little attention has been paid to neuronal cell death in CA2 sector.
In this study, we applied the rat hippocampal slice culture technique to test whether the
CA2 sector is more resistant than other sectors to chronic stimulation with bicuculline (BiC),
a GABAA receptor antagonist [1][2]. The results indicated that selective neuronal cell deathin the CA2 sector is induced by exposure to BiC for 12 h (Fig. 1A). After 24 h, cell death
was observed in an extended area, predominantly in the CA3 sector. We investigated thetype of voltage dependent calcium channel (VDCC) involved in the cell death. It was
revealed that the neuronal cell death process involves a Ca2+ influx (Fig. 1B) via P/Q-type
VDCC [1].
[１] C. Han, N. Kasai, K. Torimitsu, Neuroreport 16 (2005) 333-336.
[2] C. Han, N. Kasai, K. Torimitsu, Bul. JSN. 42 (2003) 238.

Fig. 1. Time- and region-dependent neuronal cell death (A) and Ca2+ influx (B) were
induced by exposing the hippocampal slice cultures to BiC.

- 28 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

First-principles Study of Interfacial Reaction Mechanism during Silicon
Thermal Oxidation Process
Hiroyuki Kageshima and Masashi Uematsu
Physical Science Laboratory
Silicon thermal oxide films are essential elements in fabricating silicon-based devices aswell as even in future silicon devices. We have been studying the unified understanding on
the mechanism of the silicon thermal oxidation process so as to control the process precisely
in the atomic scale.
The oxidation process is generally thought to consist of two sequential processes; theoxygen diffusion process through the covering oxide films and the oxygen reaction processwith the silicon substrate at the interface. However, we think the oxygen reaction process
should be further classified in two processes; oxygen incorporating process with the substrate
and the strain releasing process by the structural transformation. Our picture is supported byrecent isotope experimental results, which show the back flow of some reduction species
from the interface into the oxide [1].
For the oxygen incorporation process, first principles studies have revealed that there are
not so high reaction barriers as expected by the general understandings (Fig. 1) [2]. Thus, thisprocess does not necessarily govern the interfacial reaction speed. This is because the bondsof the oxygen molecule and of the Si substrate do not completely break through theincorporation process.
For the strain releasing process, first principles studies have revealed that the high-densityoxide regions with oxygen vacancies (Fig. 2) formed at the interface play important roles [3].
Even though these regions accompany the oxygen vacancy, there is no broken dangling bondbut only the covalent bonds, being consistent with experimental quite low densities of electricand magnetic defects. These regions can be regarded as regions with interstitial SiO
molecules, being consistent with the isotope experiments mentioned above.
[1] S. Fukatsu et al., Appl. Phys. Lett. 83 (2003) 3897.
[2] T. Akiyama and H. Kageshima, Surf. Sci. 576 (2005) L65.
[3] H. Kageshima et al., Jpn. J. Appl. Phys. 43 (2004) 8223.

1.333
1.638

1.618
1.607

1.611

Fig. 1. Energy profile in the oxygen
incorporation process into the substrate

Fig. 2. Structure of high-density oxide
regions with oxygen vacancies- 29 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Room-temperature single-electron transfer and detection
with silicon nanodevics
Katsuhiko Nishiguchi, Akira Fujiwara, Yukinori Ono, Hiroshi Inokawa, and *Yasuo Takahashi
Physical Science Laboratory, *Present address: Hokkaido university

Single-electron
turnstile
100nm
FET1
FET2
（b）

Single-electron box Memory node
（SEB)
（MN)
Fig. 1.（a）SEM image. （b）Schematic
view of the single-electron turnstile.

Electrometer current [nA]Single-electron devices (SEDs) have great attention because of their ultra-low power
consumption. The single-electron turnstile, which transfers electrons one by one, is a memberof the SED family and is a promising device for an architecture which treats one electron.
This architecture requires precise control of electron movement and accurate detection of
single electrons. Although various studies demonstrated these two key points, the operation
temperature has remained quite low because the devices were not small enough to prevent
thermal energy disturbing electron movement and to gain sufficient sensitivity for singleelectron detection.
We thus proposed the silicon nanodevices which can transfer and detect single electrons
and fabricated them on a silicon-on-insulator (SOI) (Fig. 1) [1]. The single-electron turnstile
is composed of two wire-FETs. A single-electron box (SEB) is electrically defined between
FETs. By turning on FET1 and FET2 alternately, the single electron is transferred to thememory node (MN) through the SEB (the inset of Fig. 2). One transfer cycle for injecting thesingle electron in the MN is composed of four steps shown in the inset of Fig. 2 [2]. By
repeating the transfer cycles, the electrons are transferred one by one. The single electronstransferred into the MN are detected by an electrometer capacitively coupled to the MN. The
electrometer is carefully positioned close to the MN so that the sensitivity of the electrometeris high enough to detect single electrons in the MN [3].
Figure 2 shows changes in the electrometer current when transfer cycle was repeated.
Current change per transfer cycle was caused by one electron transfer. The size reduction of
the SEB and optimized operating conditions allowed the single-electron transfer anddetection at room temperature. The present device using FETs for the electron transfer andstorage achieves high-speed transfer (<10ns) and long retention (>104s). We also
demonstrated that the present device could serve as a multi-level (5 bit) single-electron
memory [1].
[1] K. Nishiguchi, et al., International Electron Devices Meeting (IEDM) (2004) 199.
[2] A. Fujiwara, et al., Appl. Phys. Lett. 84 (2004) 1323.
[3] K. Nishiguchi, et al., Appl. Phys. Lett. 85 (2004) 1277.
electronpoly-Si gate（a）
電子
Electrometer

0

0.98

1
0.96

2
3

0.94 Room temperature 4# of electrons： 5
0.92

0

2
3
4
5
6
# of transfer cycles
Fig.2. Single-electron transfer and detection- 30 -

1

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Integrated carbon multi-probe with nano-spring on Si cantilever
Masao Nagase
Physical Science Laboratory
Multi-probe systems based on scanning probe technology are expected to become apowerful tool for measuring electrical properties in high resolution. We have demonstrated afeasibility of a new multi-probe system. Four carbon probes with nano-springs have been
integrated on a silicon cantilever with aluminum electrodes by using focused-ion-beamchemical-vapor-deposition (FIB-CVD) technique. Diamond like carbon (DLC) deposited by
FIB-CVD is known to be stiff and conductive. These properties are suitable for electricalprobes. Recently, Matsui et al. have demonstrated the fabrication of the coil spring structureusing FIB-CVD technique. [1] The nano-springs are expected to compensate for the height
difference between the probes which are not adjustable in conventional probe systems. [2]Figure 1 is a schematic and microphotographs of four carbon probes on a Si cantilever.
The three-dimensional FIB-CVD structures are fabricated by SMI2050 (SII-NT) in Univ. of
Hyogo. [1] The height of the probe with nano-spring is about 10µm. The diameter of theprobe is 110 nm. The coil diameter of the nano-spring is 380 nm. Figure 2 shows theelectrical contact characteristics between the conductive sample and one of the probes. The
origin of the displacement axis is the set point for AFM imaging in contact mode. The
triangle mark (contact height) indicates that this probe establishes electrical contact with thesample at 580 nm. Since the displacement of the Si cantilever is about 200 nm at the set point,
the nanospring is shortened by about 400 nm. Every probe contacts the sample surface even if
the heights of probes are different, because the probe can shorten freely. Therefore, the nanosprings compensate for any height differences. The mechanical characteristics are also
confirmed in a tensile test of the nano-spring grown on a conventional Si cantilever. The
shear modulus of the nanospring is estimated to be almost the same as that of theconventional steel spring. Since no deformation of the FIB-CVD probes is observed after
imaging by atomic force microscopy (AFM) in contact mode, the stiffness of the probes issufficiently high.
Combining scanning probe technology and focused ion beam technology will open a newarea of micro- and nano-electromechanical systems.
[1] S. Matsui et al., J. Vac. Sci. & Technol. B 18 (2000) 3181.
[2] M. Nagase et al., Jpn. J. Appl. Phys. 42 (2003) 4856.

Fig. 1. (a) Schematic of four-point -probe on Si
cantilever. (b) SEM micrograph of integrated
FIB-CVD multi-probe. (c) Magnified image ofcarbon probe with nano-spring on Al electrode.
- 31 -

Fig. 2. Displacement dependence ofprobe current. Voltage of the sample(Au film) is 1V.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Force/Displacement Detection Using Electron Interference
Hiroshi Yamaguchi and Yoshiro Hirayama
Physical Science Laboratory
Ultra-small force and displacement have been detected using a small bar, clamped at one
end like a diving board, known as a cantilever. It is already used in practical systems, such as
in the pickups for analog disks, atomic force microscopes, and the accelerometers ofautomobile airbag systems. Especially, the micron-scale cantilevers play essential roles in thetechnology using microelectromechanical systems (MEMS), which has made rapid advancesin the last few years. For detecting the cantilever deflection, both optical and electricalmethods are widely used. Optical methods, such as optical levers and laser interferometers,
offer higher detection sensitivity than electrical ones. They have been recently used even forthe detection of single spins [1]. In contrast, electrical methods are advantageous fordownscaling and integration. In addition, we could strongly enhance the detection sensitivity
in piezoresistive cantilevers, which is one of the most important electrical methods, using thequantum effects in semiconductor low-dimensional structures.
At low temperatures, electrons exhibit wave-like behavior, so they can be used for highly
accurate sensing just like the photons in a laser interferometer. We have succeeded in
detecting the displacement of a micromechanical cantilever by using electron interference [2].
The device used was an InAs/AlGaSb pieozoresistive cantilever with the thicknesses ofconductive InAs and insulating AlGaSb films of 15 nm and 285 nm, respectively. A scanningelectron microscope image of a typical fabricated device is shown in Fig. 1. The resistancechange induced by the cantilever deflection was measured under a magnetic field (Fig.2). The
magnetic field was used to adjust the phase differences among different electron paths in the
InAs films. The resistance change, i.e. the cantilever deflection sensitivity, has a strong andaperiodic B dependence, which was reproducible in repeated measurements. At 6.9 T, theresistence change had a maximum value, which was nearly one order of magnitude larger
than that at zero magnetic field. This clearly demonstrates the possibility of highly sensitive
quantum mechanical displacement sensing, which is promising for future micromechanicalcantielver applications.
[1] D. Ruger et al., Nature 430 (2004) 329.
[2] H. Yamaguchi et al, Phys. Rev. Lett. 93 (2004) 036603.

2.5 K

Fig. 1 SEM image of a fabricatedpiezoresistive cantilever.

Fig. 2 Measured resistance change asa function of magnetic field.

- 32 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Landau-level hybridization and the quantum Hall effect in
InAs/GaSb electron-hole systems
Kyoichi Suzuki, Kei Takashina, and Yoshiro Hirayama
Physical Science Laboratory
In InAs/GaSb heterostructures, the conduction band in InAs and the valence band in
GaSb overlap. Consequently, a two-dimensional electron gas (2DEG) in the InAs and a twodimensional hole gas (2DHG) in the GaSb can coexist in close proximity. A uniquequantum Hall effect (QHE) has been known to occur in these structures where the Hall
resistance is quantized by the difference between2DEG and 2DHG Landau-level (LL) fillingfactors (νe, νh). Its mechanism had yet to be clarified, and had been thought to be a complex
combination of QHE arising in both 2DEG and 2DHG.
We clarified the mechanism using back-gated structures (Fig. 1) and detailed magnetotransport measurements. The samples consisted of an InAs 2DEG layer on the surface side
and a GaSb 2DHG layer on the substrate side. We succeeded in controlling the 2DHG
density with the gate voltage, while keeping the 2DEG density constant by the surface
potential. Changing the thickness of the inserted AlSb layer between the InAs and GaSb
layers, which works as a potential barrier for both 2DEG and 2DHG, the hybridization
strength between 2DEG and 2DHG wavefunctions can be controlled. Under magnetic field,
in samples without wavefunction hybridization, the electron and hole energy levels split into
LLs shown as the dashed lines in Fig. 2. In samples where wavefunction hybridization isallowed, however, LLs also hybridize (solid lines) and a new energy structure is formed, inwhich the region of νe=νh becomes effectively the band gap. Net carriers (difference of
2DEG and 2DHG densities) fill the hybridized LLs above the band gap. Therefore,
conventional 2DEG-like QHE occurs, according to the net carrier density.
We believe our results will become useful for realizing new physics phenomena reflecting
electron-hole interactions and correlations, such as Bose-Einstein condensation of the dipole
excitons, and contribute to the development of mid-infrared device applications using intersubband transitions and inter-layer tunneling.
[1] K. Suzuki et al., Phys. Rev. Lett. 93 (2004) 016803.
Conduction
band

3
2
Al0.7Ga0.3Sb

AlSb

GaSb

GaSb
Cap

InAs
Electron

AlSb/GaSb
Superlattice

Hole

EF

InAs
Substrate

EnergyAl0.7Ga0.3Sb(AlSb)

Fig. 1. Sample potential profile

Band gap
H1

E4

H2
E3
E2

VG

1

E1
Magnetic field

H3 Valenceband
H4Fig. 2. Landau-level hybridization
Dashed lines: Electron and hole Landau-levels without hybridization.
Solid lines: Hybridized Landau-levels.

- 33 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Controlled Valley Splitting in SiO2/Si/SiO2 Quantum Wells
Kei Takashina, Akira Fujiwara and Yoshiro Hirayama
Physical Science Laboratory
Besides being of immense technological importance, electrons in silicon offer a number of
unique possibilities for exploring new physical conditions and new phenomena. One of thesearises due to their bulk dispersion relation where there are six, energetically degenerate
conduction band valleys. In (100) Si-MOSFETs where electrons are two-dimensionallyconfined, this six-fold degeneracy is lifted, due to anisotropic effective mass, to leave only
two low lying valleys available for occupation. 2-D electrons in such structures consequently
have freedom as to how they occupy these degenerate valleys giving them a valley degree of
freedom on top of in-plane motion and spin.
In the present study, we have been able to show that valley-splitting, which lifts thisremaining two-fold valley degeneracy can be controlled over an unprecedented extent using
SOI (Silicon-On-Insulator) MOSFETs. These structures consist of silicon sandwitchedbetween layers of SiO2 forming SiO2/Si/SiO2 quantum wells. Since there are two Si-SiO2
interfaces present in such structures, by using interfaces with different properties, electronic
properties can be readily tuned by shifting the wavefunction between them. Here, we haveused SIMOX (Separation by IMplantation of OXygen) MOSFETs where we find the valleysplitting to be strongly enhanced at the Si-buried oxide interface. The valley splitting cantherefore be tuned, simply by adjusting front and back gate voltages to shift the wavefunction
between the interfaces with small and large valley splitting [1,2].
[1] T. Ouisse, D.K. Maude, S. Horiguchi, Y. Ono, Y. Takahashi, K. Murase and S.
Christoleanu, Physica B, 249-251, 731 (1998)[2] K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, Y. Hirayama, Phys. Rev. B, 69,
161304(R), (2004), K. Takashina, Y. Hirayama, A. Fujiwara, S. Horiguchi, Y. Takahashi,
Physica E, Vol 22, 72 (2004)

VBG (V)

10

20

30

6

VFG (V)

4

2

6

8
7

4
3

0

5

-2

Rxx

High

Low
1.200
1.087
0.95160.8156
0.67970.54380.40780.27190.1359 0

Left: A schematic diagram of Landau levels with increased valley-splitting.
Right: Longitudinal resistance at 11T. Numbers indicate filling factors associatedwith quantized Hall states.
- 34 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Single-Electron Counting of Electrical Current
Toshimasa Fujisawa
Physical Science Laboratory
Electrical current is widely used in various electronic systems, and is one of thefundamental measurement for electron transport phenomena. However, the minimum
detectable current is remained at around 105 – 106 electrons/sec. Recent development in
nanotechnology research enables us to manipulate single electron in a small conductive island(quantum dot). More recent activities are devoted to some applications, such as singleelectron transistors and memories, as well as physical interests on electronic states inquantum dots. In this study, we have succeeded in observation of each electron tunneling
events through a quantum dot in real time scale, which is expected to be applied to extremely
sensitive ampere meter that counts how many electrons has passed through a device.
In this work, we prepare two quantum dots (the upper one and the lower one) coupledelectrostatically, and the current through the upper dot can be detected with a change in thecurrent through the lower dot [1]. Electron counting can be realized since the current throughthe lower dot decreases (increases) when an electron enters (leaves) the upper quantum dot.
The device used in this study is shown in the SEM picture of Fig. 1. Two quantum dots
(denoted by circles) embedded in isolated two electrical channels is fabricated in
AlGaAs/GaAs modulation-doped heterostructure by etching process (dark regions) and fine
Schottkey gates (bright vertical lines). We feed a small current through the upper quantum
dot, and tunneling events can be measured with the conductance through the lower dot. In
order to improve the frequency band width, high-frequency carrier signal (660 MHz) is
introduced, and the transmitted signal is amplified with LC resonator and detected with amixer. The output voltage, Vdet, is proportional to the conductance of the lower dot.
Figure 2(a) shows typical time dependent signal Vdet, when the upper quantum dot isadjusted at the Coulomb blockade (CB) condition and at the single-electron tunneling (SET)
condition. Binary switching signal is appeared in the SET condition, and double peak feature
is observed in the histogram of Vdet taken with a loger period (shown in Fig. 2(b)). Therefore,
we are able to determine when an electron enter the upper dot (denoted by white circles inFig. 2(a)) and when an electron escape to the electrode (solid circles). In this case, there are
five tunneling events within the 10 ms period, corresponding to 0.08 fA of current. We expect
to develop an electron counting device for either current direction in future.
[1] T. Fujisawa et al., Appl. Phys. Lett. 84, 2343 (2004).

Fig. 1. Measurement system and an electron
counting device.
- 35 -

Fig. 2. Single-electron counting (SET)and background noise (CB)Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Fast control of qubit coherence with phase shift method
Hirotaka Tanaka, Tatsuya Kutsuzawa, Shiro Saito
Physical Science Research Laboratory
A superconductor ring with Josephson junctions behaves as quantum 2-level system andis expected to be a candidate for a quantum bit (qubit), which is a key ingredient of quantum
computer( Fig. 1). We controlled and measured the quantum coherence of this ring using two
sequential microwave pulses with phase shifted. This ring has two different states of opposite
directions of current flowing in clockwise and anti-clockwise and shows the quantum
superposition of these states. The size of the ring is about 10μm, which is much larger thanthat of atoms or molecules but it still shows quantum nature of 2-level system. We
experimentally confirmed that the ring shows quantum superposition between |0> and |1>states. The quantum superposition in a macroscopic scale object is sometimes called
Schrödinger’s cat.
We utilized phase shift method, which uses simultaneous phase-pulse modulation of
microwave pulses. Two sequential microwave pulses are applied to the ring with frequencyof 11.4 GHz and duration of 5 ns. The phase of the pulses is continuously shifted. The first
pulse makes the state of the ring superposition of |0> and |1>. (The point on the equator in thesphere in Fig. 2) The state of the ring has its phase coherence depending on the phase of thefirst pulse. Then second pulse transforms the state of the ring depending on the phase of thesecond pulse. (The point on the equator, north and south pole in the sphere in Fig. 2)
We experimentally showed the fast and effective quantum coherent control with the phaseshift method[1]. It can be applied also to Hadamard gate, which is an important gate
operation in quantum computation. In addition, the phase shift method allows us to choose
optimum pulse sequences in a 2-qubit system for fast and effective operations.
[1] T. Kutsuzawa, et al., Appl. Phys. Lett. 87, (2005): (accepted). ArXiv : cond-mat/0501592.
50

10000 Counts
TPhaseShift=89 ps

Psw [%]

45
40
35

Fig. 1 Scanning electron microscope
picture of superconductor qubit. Inner
squared loop is a qubit and outer is a
DC-SQUID(Superconducting quantum
interference device) for readout.

30
1.0

1.2

⊿Φ＝０

⊿Φ＝π/21.4
1.6't 12 [ns]

⊿Φ＝π

1.8

2.0

⊿Φ＝3π/2

Fig. 2 Qubit state measurement with two
pulses applied. The state is oscillating by the
relative phase of the microwave pulses.

- 36 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Quantum Computation with Neutral Atoms
Tetsuya Mukai, Taro Eichler, Alexander Kasper, and Fujio Shimizu*
Physical Science Laboratory*NTT Research Professor and University of Electro-Communications
Neutral atoms are promising candidate to realize quantum gates. The advantage of using
neutral atoms for quantum computation is as follows. 1) We can make arbitrary amplitude
distribution among internal states with laser light. Therefore, single-qubit operations are easy
and accurate. 2) Two qubits operations are possible with atom-atom interactions or indirectly
via an auxiliary quantum system. 3) Disturbance from external fields to neutral atoms isrelatively weak, and decoherence time is very long. 4) All atoms are identical and we can
expand number of qubits without taking care of the characteristics of individual qubits. 5) We
can fill qubit locations with few defects from Bose-Einstein Condensate (BEC). However, theprogress of neutral-atom quantum computer is slow because implementation of all necessaryfunctions in a system is not easy.
Recent progress in laser cooling of atoms enables us to cool down atomic samples to atemperature below one micro-Kelvin and to make 2- or 3-dimensional array of neutral atoms.
Employing high-quality micro-fabrication technology and our experiences in laser andefficient evaporative cooling for making BEC [1], we are trying to develop a model quantum
computation system with ultra-cold neutral atoms.
In the first project we plan to use 2-dimensional magnetic trap arrays. It consists of microfabricated Z-shaped wires on a silicon surface. To realize an array of single atoms in the
ground vibrational state and to ensure atom-atom interaction we have to reduce the distance
between atoms and surface. This short distance introduces extra potential noises and shortdecoherence time. We are trying to overcome this problem with super-conducting wires onsilicon substrate (Atom Chips).
In the second project we use an optical lattice. We have proposed a scheme to realize ascalable quantum computer with double optical lattices [2]. Employing this scheme we cancompose an universal quantum computer with complete scalability and we hope to achieve apractical quantum computer with more than 1000 qubits operating together. We are trying to
implement the double optical lattices scheme to a real system.
[1] T. Mukai and M. Yamashita, Physical Review A 70 (2004) 013615.
[2] F. Shimizu, Japanese Journal of Applied Physics 43 (2004) 8376.

Fig. 1. Sample Atom Chips

Fig. 2. Pattern of wire

- 37 -

Fig.3. Double Optical Lattice

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Spin Interferometer by the Rashba Spin-Orbit Interaction
Y. Sekine1, T. Koga1,2,*, and J. Nitta1,3,‡
Physical Science Laboratory1, PRESTO JST2, CREST JST3
Experimental demonstration of an electric-field-controllable spin interferometer isreported. In this study, we focused on the spin degree of freedom rather than the charge
degree of freedom used in conventional semiconductor devices. The electron spin is usuallycontrolled by a magnetic field; however, it has been demonstrated that the electron spin
precession can be controlled by an electric field. These results are the first step towards new
functional devices that utilize the spin degrees of freedom of electron.
A key to controlling electron spin in a semiconductor is the Rashba spin-orbit interaction,
which makes it possible to control the spin precession by an electric field. Figure 1(a)shows a scanning electron microscope (SEM) image of the semiconductor spin
interferometers. An array of square loops was fabricated by the electron beam lithography
and a dry etching technique. The lighter region contains the electron path, and a typical pathis outlined by the black square. Figure 1(b) shows a schematic view of the sample. The
entire sample is covered with a voltage-gate electrode, which makes it possible to control the
spin precession due to the Rashba spin-orbit interaction. The Al’tshuler-Aronov-Spivak(AAS) oscillations were observed to investigate the angle of the spin precession. Twopartial electron waves that travel along the four sides of the square in the clockwise and thecounter-clockwise directions interfere each other. Due to the Rashba spin-orbit interaction,
the spin precession occurs as these waves pass through the square loop. The interference
depends on the difference of the angle of the spin precession. The gate voltage, Vg,
dependence of the AAS oscillation amplitude is shown in Fig. 2. With increasing Vg, thesign of the conductivity, σxx, without a magnetic field, B, changes from minus to plus.
These results show that the electron spin interference is realized by the electric-fieldcontrollable spin precession.
[1] T. Koga, J. Nitta, M. van Veenhuizen, Phy. Rev. B 70, 161302(R) (2004).
Present Address: Graduate School of Information Science and Technology, Hokkaido
University*, Graduate School of Engineering, Tohoku University‡.
Fig. 1(a)Fig. 2
2

σxx [µS]

1 µm

1
0

-1
-2
2

VH-

Gate

I+

I-

V+

200 µm

VVH+

125 µmσxx [µS]

(b)

1
0

-1
-2
-4

Fig. 1. (a) A SEM pictureof the spin interferometers.
The black square represents
Vg=-1.2V
a typical electron path. (b)A schematic view of thesample. The entire sample
is covered with a voltagegate electrode.
Vg=0V Fig. 2. The gate voltage
dependence of the AAS
oscillations. The sign ofσxx at B=0 changes fromminus to plus.
Theelectric-field-controllable
spin precession results in themodulation of the spin
-2 0
2 4interference.

B [mT]- 38 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Electron-Spin Control based on RKKY Interaction
Hiroyuki Tamura
Physical Science Laboratory
We theoretically proposed a method to control electron-spin state electrically by tuning amagnetic interaction between local spins confined in quantum dots and conduction electrons
in semiconductors [1]. When quantum dots confining electrons are coupled to conducting
semiconductors, the conduction electron can jump into and out of the quantum dot andinteract with the confined electron in it. This process induces an antiferromagnetic interaction
between the confined electron and the conduction electron. When two quantum dots arecoupled to the conducting semiconductor as shown in Figure, the conduction electron can goback and forth between two dots. If the distance of two dots is much smaller than the Fermi
wavelength, the conduction electron can travel without losing spin orientation and the
localized spins in dots are aligned in the same direction, which results in a ferromagnetic
interaction known as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Since thedegradation of spin orientation depends on the electron density in the conduction region, one
can tune the spin state both in parallel and anti-parallel way by changing gate voltages.
The key for electric control of spins is the artificial magnetic impurities formed in thequantum dots and the tunable electron-density in semiconducting materials. These features
make it possible to realize a new type of spintronics device.
By utilizing the RKKY interaction, one can expect to achieve ferromagnetism in an arrayof semiconducting quantum dots where all the spins are aligned in the same direction.
Experimental search for detecting the RKKY interaction between dots has already started [2],which will help to prove our theoretical prediction.
[1] H. Tamura, K. Shiraishi, and H. Takayanagi, Japan Journal of Applied Physics 43 (2004)
L691-693.
[2] N. J. Craig, J. M. Taylor, E. A. Lester, C. M. Marcus, M. P. Hanson, and A. C. Gossard,
Science 304 (2004) 565-567.

Quantum dot 1
with down-spin

Quantum dot 2
with down-spin
Figure: Two quantum dots coupled
to the conduction electron system.
Electron spins in two dots arealigned in the downward direction
when the conduction electron with
opposite (up) spin jumps back andforth between two dots.

QD-1

Conduction electron with up-spin- 39 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Generation of telecom-band polarization entangled photon pairs
using spontaneous four-wave mixing in dispersion-shifted fiber
Hiroki Takesue
Optical Science Laboratory
Generation of entangled photon pairs in the 1.5 µm band is one of the important
technological challenges for realizing quantum communication over optical fiber networks.
We have succeeded in generating polarization entangled photons in the wavelength band, byusing spontaneous four-wave mixing (SFWM) in a loop formed with a polarization
beamsplitter (PBS) and a dispersion-shifted fiber (DSF).
Fig. 1 shows the configuration. A pump pulse with a 45°linear polarization is input into
the loop. The PBS divides the pump into horizontal (H) and vertical (V) polarization
components. The H and V components generate signal-idler photon pairs H s H i andV s V i through a SFWM process while propagating in the loop in the counter-clockwise
and clockwise directions, respectively. These two product states are superposed at the PBS
output, the pump is then suppressed, and a polarization entangled state
H s H i+V sV i
2 is obtained. The loop configuration makes it possible to stabilize
the relative phase between two product states without any feedback control, and so oursystem is both simple and stable.
We confirmed the feasibility of our method experimentally. We used fiber-Bragg gratings(FBG), an arrayed waveguide grating (AWG) and bandpass filters (BPF) to suppress thepump and separate the signal and idler photons. The signal and idler photons werepolarization-controlled and input into polarizers, and detected using avalanche photo diodes(APD). We undertook two-photon interference experiments, and obtained coincidence fringes
with >90 % visibilities, which is shown in Fig. 2. We then observed a violation of Bell's
inequality by seven standard deviations. We also confirmed the preservation of the quantum
correlation between the photons even after they had been separated by 20 km optical fiber.
This result is an important step toward highly sophisticated quantum communication
networks over optical fiber.
[1] H. Takesue and K. Inoue, Phys. Rev. A, 70, 031802(R) (2004).

()

Fig. 1. Configuration

Fig. 2. Coincidence fringes- 40 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Differential-phase-shift quantum key distribution experimentToshimori Honjo and Kyo Inoue
Optical Science Laboratory
Quantum key distribution (QKD) has been studied as a way to realize unconditionallysecure communications. We proposed a new QKD scheme called a differential-phase-shift
QKD (DPS-QKD). This scheme has several advantages including suitability for fibertransmission. This study demonstrates a feasibility of DPS-QKD by using a glass waveguideinterferometer.
Fig. 1 shows the experimental setup. The signal source was an external-cavity laser
diode(λ=1551 nm). Cw light from the laser was converted into a pulse stream by anintensity modulator, and then was randomly phase-modulated for each pulse by {0,π}. The
pulse width was 125 ps and the repetition rate was 1GHz. The light power was attenuated tobe 0.1 photons per pulse. After 20-km fiber transmission (4.46-dB propagation loss), the lightpassed through a glass waveguide Mach-Zehnder interferometer packaged with fiber ports.
The path-length difference was 20 cm, which introduced one-bit delay of 1 ns at 1 Gbit/s. The
waveguide is made of silica glass by using PLC (planar lightwave circuit) technology, and theexcess loss of the interferometer was only 2.64dB. The polarization dependence was small,such that the extinction ratio of the interferometer ranged from 0.27% to 0.46% when the
input polarization state was changed. The two outputs from the interferometer were received
by APDs gated at 5 MHz. After the photon transmission, Bob told Alice the photon arriving
time, from which a key was created. Since APDs had time jitter, the arrival time of photons
vacillated and errors could be induced. To reduce this timing error, Bob took data within atime window, at the expense of the key generation rate. Fig. 2 shows the raw key generation
rate and quantum bit error rate (QBER) for several time windows, where the polarization
state was set to give the worst QBER. A sufficient QBER was obtained to create a secret key
after error correction and privacy amplification.
In summary, a differential-phase-shift QKD experiment was carried out using a glass
waveguide Mach-Zehnder interferometer. Stable polarization-insensitive operation wasdemonstrated in 20-km fiber transmission. The key creation rate was 3076bit/s with a 5.0%
QBER.
[1] K. Inoue, E. Waks and Y. Yamamoto, Phys. Rev. A 67, (2003) 022317.
[2] T. Honjo, K. Inoue and H. Takahashi, Opt. Lett. 29, (2004) 2797.

1 GHz
External
Cavity Laser(λ = 1551nm)

Pulse
Pattern
Generator
1 GHz

Intensity
Modulator(LiNbO3)

Phase
Modulator

0.1
photon/pulse
Attenuator(LiNbO3)

Glass-waveguideMach-ZehnderInterferomter
Optical Fiber

Bob
Pulse
Generator
5 MHz
Det
Det

20 km
(4.46 dB)

20 cm
(2.64 dB)

(APD)

Time
Interval
Analyzer(TIA)

QBER(%)

Pulse
Generator

Raw Key Generation Rate (bps)

AliceTime Window (nsec)

Fig. 1. Experimental setup

Fig. 2. Experimental results- 41 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Time-resolved EXAFS
Katsuya Oguri, Yasuaki Okano, Tadashi Nishikawa and Hidetoshi Nakano
Optical Science Laboratory

Intensity [a. u.]

The recent development of various ultrashort x-ray-pulse sources based on high-power
femtosecond lasers has stimulated progress on ultrafast time-resolved x-ray probing
techniques with femtosecond or picosecond resolution. In particular, the time-resolved
extended x-ray absorption fine structure (EXAFS) approach is expected to become apowerful technique for probing ultrafast structural dynamics, because EXAFS provides such
structural properties as bond distance and coordination number for various materials
including amorphous materials and liquids [1]. Here, we present a time-resolved EXAFS
technique with picosecond resolution that employs a soft x-ray pulse emitted fromfemtosecond laser-produced plasma. By employing this technique, we successfully
observed the time evolution of an ultrafast melted Si L-edge EXAFS induced by femtosecond
laser irradiation [2].
We constructed an experimental laser-pump and x-ray probe setup based on a 100-fs
Ti:sapphire laser system. Figure 1 shows an example of the absorption spectrum of Si foil.
We clearly observed the LII,III edge at 99 eV, the LI edge at 150 eV, and the damped
oscillation, which corresponds to EXAFS, in the region of 150 – 270 eV. Figure 2 shows
the time evolution of the EXAFS spectrum at various time delays, which was extracted fromeach absorption spectrum. We can clearly see that the oscillation amplitude decreases witha small peak shift to a lower wave number at a time delay of 0 ps while there is no great
difference between the EXAFS spectra of the pumped and unpumped samples at a time delayof -330 ps. The small peak shift indicates that the oscillation period becomes shorter thanthat of the unpumped Si and this strongly suggests that the Si-Si atomic distance wasbroadened slightly by the laser excitation. We obtained a Si-Si atomic distance of 2.43 Å,
which is clearly larger than the value of 2.32 Å for solid Si obtained by Fouriertransformation of the data. This expansion of the atomic distance can be explained in termsof the ultrafast production of liquid Si. At a time(a)delay of +1670 ps, the EXAFS becomes too weakfor us to analyze its oscillation structure. The
disappearance of the oscillation indicates thefurther structural disordering of Si due to the-330 ps
onset of evaporation from the liquid phase to the(b)gas-like phase. This result is the first step
towards establishing ultrafast time-resolved
EXAFS technique.
[1] T. Lee et al., Chem. Phys. 299 (2004) 233.
~0 ps
[2] K. Oguri et al., Appl. Phys. Lett.87(2005)011503
(c)
LI

µd(E)

2.0
1.5
1.0

+1670 ps
LII,III

0.5
100

Fig. 1.

4.0

EXAFS

150
200
Energy [eV]

4.5

5.0

5.5
-1

Wave number [Å ]250

Example of Si-absorption spectrum.

- 42 -

Fig. 2. Transient EXAFS spectrawith (thin black line) and without(thick gray line) laser irradiation.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Exciton and Biexciton Coherent Effects in Quantum Dots
Hideki Gotoh and Hidehiko Kamada
Optical Science Laboratory
Semiconductor quantum dots have discrete density of states and exhibit strong interaction
effects with light. Moreover, optically created excitons and biexcitons exist stably in quantum
dots because of confinement effects from all spatial directions. These features promise
possible future applications of quantum dots for quantum information processes. In quantum
dots, there may be coherent interactions between excitons and biexcitons and the effects ofthese interactions have not yet been clearly observed. These effects provide a source ofquantum correlations by exciton-biexciton interactions and a principle of optical functions byquantum interference effects.
We examined the photo-absorption properties of excitons and biexcitons in a single
InGaAs quantum dot. The coherent effects may appear in these absorption properties. We
employed a micro-photoluminescence (PL) method. Figure 1 shows measured absorption
spectra of exciton (X) and biexciton (XX) for two excitation conditions. At a low excitation,
we obtained usual peak shaped absorption spectra. However, these spectra change greatly
with a high excitation. The XX spectrum has a broadened peak. In contrast, the X spectrum
has an unusual dip-shaped structure. Figure 2 reveals the physical origin of the unusual
spectrum. The figure shows the energy level structure for the measurement result. The energy
structure is a coherently interacting three-level system with ground, exciton and biexciton
states. This structure varies greatly with excitation. With a high excitation, the exciton andbiexciton states split due to Rabi oscillation between the exciton and biexciton states. This
causes the exciton state to vanish resulting in the dip-shaped exciton absorption. This Rabi
oscillation is a coherent effect and our result confirms that there is a strong coherent effect inthe exciton and biexciton states.
Our results are an important step towards achieving a quantum two-bit gate with an
exciton and a biexciton. Moreover, this provide a possible way to demonstrate optical device
functions with quantum interference effects.
[1] H.Gotoh, et al., Appl. Phys. Lett. 85 (2004) 3480.
[2] H.Gotoh, et al., Phys. Rev. B in press
Low Excitation

High Excitation
Low Excitation

Intensity (a.u.)

X

X

High Excitation

XX

XX

XXD

X

X

XD

XX

Absorption
vanishes:
Dip structure
g

XX

g

1.698 1.700 1.702 1.698 1.700 1.702
Photon Energy (eV) Photon Energy (eV)Fig. 1. Exciton and biexciton absorption.

Fig. 2. Energy level structure- 43 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

InGaN Cavity Polaritons
Takehiko Tawara1, Hideki Gotoh1, Tetsuya Akasaka2 and Toshiki Makimoto2
1
Optical Science Laboratory, 2Materials Science Laboratory
Cavity polaritons are quasi-particles that are created by strong exciton-photon coupling ina semiconductor quantum well (QW) microcavity. In recent years, much attention has been
directed to the behavior of these cavity polaritons as composite bosons at sufficiently small
densities. One area of interest relates to polariton devices that employ bosonic behavior, suchas the threshold-less “polariton” laser. To achieve these devices and room temperature
operation, we have to choose materials that have large oscillator strength and a large exciton
binding energy.
GaN-based semiconductors have a large exciton binding energy, and this energy allows
excitons to exist even at room temperature. Moreover, the oscillator strength of this system
will be larger than that of typical III-V semiconductors owing to the large effective mass ofnitrides. Therefore, we can expect very strong exciton-photon coupling in GaN-based QW
microcavities that will enable us to achieve polariton devices that operate above room
temperature.
We used smooth and crack-free InGaN QW microcavities to realize strong coupling. The
microcavities were fabricated using a wafer bonding technique with an InGaN/AlGaN QWlayer and dielectric DBRs (Fig. 1). We observed a lasing action in the fabricated microcavity
as shown in Fig. 2 [1]. Figure 3 shows the reflection spectra of the QW microcavities forvarious degrees of cavity detuning (δ). We observed the appearance and disappearance ofsplitting and these positions varied with δ. This behavior is evidence of cavity polariton
formation, and the vacuum-field Rabi splitting which reflects the strength of the excitonphoton coupling is about 6 meV. We deduced from these results that the oscillator strength of
InGaN QW excitons is one order of magnitude larger than that of GaAs QW excitons. These
results indicate that GaN-based semiconductors are advantageous for studying the polaritonic
effect and its device applications.
[1] T. Tawara, et al., Appl. Phys. Lett. 83 (2003) 830.
[2] T. Tawara, et al., Phys. Rev. Lett. 92 (2004) 256402.
(a)(b)
sapphire
SiO2/ZrO2 DBR←

InGaN QWs
bonding←bonding

AlGaN
SiC

SiO2/ZrO2 DBR
dry etching

sapphire

Fig. 1. Fabrication.

Fig. 2. Lasing by
optical pumping.
- 44 -

Fig. 3. Formation ofcavity polariton.

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Fabrication and Physics of Low-Loss Photonic Crystal Slab Waveguides
Eiichi Kuramochi, Stephen Hughes, and Masaya Notomi
Optical Science Laboratory
Recently, the two-dimensional photonic crystal slab (PCS) has attracted great interest
because it has led to the development of high quality-factor photonic nanocavities and lowloss waveguides [1]. It has been revealed that a guided mode induced by a line defect in ideal
PCS is theoretically lossless when it is designed to be inside the photonic band gap and under
the light line. However, current nanolithography technology allows nanometer-order disorderand it is believed that such disorder causes a considerable loss increase due to out-of-plane
scattering.
One aim of our research is to demonstrate that waveguide loss can be reduced by reducing
fabrication disorder. We patterned PCSs by using a precise electron beam lithography systemwith 1-nm position accuracy and 100-kV acceleration, where we paid great effort tominimizing the proximity effect. We observed the fabricated Si PCS with scanning electron
microscopes and found that disorder (σ, RMS) was about 3 nm (Fig. 1). We measured the
propagation loss of PCS waveguides by the cut-back method. The minimum loss measured
was 5dB/cm (Fig. 2), which is record loss for photonic crystal waveguides [2].
Another aim of our research is to reveal the physics of PCS waveguide loss. We applied
the photon Green function tensor (GFT) formalism [3] to disorder-related scattering in theguided mode. We derived the loss formula as a simple product of the disorder and local
density of states of light between the initial state and final state. We calculated the loss
assuming σ of 3nm, and the result showed surprisingly good agreement with the experimental
data (Fig. 2). This loss calculation by our GFT method is the most detailed ever achieved. We
investigated the scattering-loss mechanism in detail by theory and experiment. We revealed
for the first time that the loss characteristics of PCS waveguides are unique and complex
because the loss mechanisms (out-of-plane scattering, intermode scattering, and backward
scattering) are tightly bound with photonic band structure.
In conclusion, by experiment and theory, we successfully revealed the detailed physics ofscattering loss in PCS waveguides caused by fabrication disorder.
[1] M. Notomi et al., Optics Express 12, 1551 (2004).
[2] E. Kuramochi et al., LEOS2004, WF6 (2004).
[3] S. Hughes et al., Phys. Rev. Lett. 94, 033903 (2005).
1000

Si
SiO2 (to be removed)

1µm

Loss (dB/cm)

200nm
100

ExperimentCalculation

1011480 1500 1520 1540 1560 1580 1600

20µm

Wavelength (nm)Fig. 1. SEM images of Si PCSs fabricatedin this study.

Fig. 2. Measured and calculated loss
spectra of PCS waveguides.
- 45 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

All-optical switches based on photonic crystal nanocavities
Takasumi Tanabe, Akihiko Shinya, and Masaya Notomi
Optical Science Laboratory

Transmission (%)

Γ−Μ
Γ−Κ
10

1

10

0

10

-1

10

-2

mode C

Transmission (a.u.)

Small cavities with strong light confinement (high-Q) can be fabricated by employing
photonic crystals (PhCs) [1], whose dielectric is periodically modulated. In such small highQ optical cavities, efficient all-optical modulation based on the light-matter interaction is
expected because the photon density inside the cavity becomes extremely high. Siliconbased integrated optical circuits are regarded to have very high potential, due to thepossibility of fusion with existing electrical devices. However, there has been some doubt as
to whether active all-optical devices can satisfy certain requirements, such as low operationenergy, high-speed operation, high switching contrast, and small device size. We will also
have to be able to cascade them on-chip. No device meeting these requirements has been
fabricated on silicon yet. Here, we demonstrated low operation energy and high-speed alloptical switching on silicon-chip based on a PhC high-Q nanocavity [Fig. 1 (top)].
The resonant transmission spectrum of a fabricated device under the linear operation
condition is shown in Fig. 1 (bottom). When the optical energy of the near-infrared light isconverted to thermal energy through the two-photon absorption process, the center of thetransmission spectrum of the nanocavity shifts because the refractive index is modulated.
By utilizing this phenomena, ultra-low-energy switching operation of a few pJ (pico=10-12) is
performed [2]. By utilizing refractive index modulation due to the carrier-plasma effect,
further operation energy reduction and switching speed enhancement are expected. As
shown on Fig. 2, the all-optical switching operation based on the carrier-plasma effect isdemonstrated at few ten fJ (femto=10-15) effective energy with a speed higher than 100 ps [3].
In the case shown in the graph, continues-wave signal light whose wavelength is slightly
detuned to shorter wavelength from Mode-S resonance is modulated with pulsed control light,
which is Mode-C resonant. This energy value and the device size are the smallest yetreported for fast silicon all-optical active devices, and these are achieved owing to the high-Q
and efficient coupling with waveguides that are simultaneously attained in our PhC
nanocavities [2].
The present result opens the way to silicon photonics; namely, the possibility of practicalhigh-speed, low-power, and high-density all-optical logic gate on-chip applications on asilicon PhC platform.
[1] M. Notomi et al., Opt. Express 12 (2004) 1551.
[2] M. Notomi et al., Opt. Express 13 (2005) 2678.
[3] T. Tanabe et al., CLEO/QELS2005,QDPA5, Baltimore (2005).

µm

0

10

-1

10

mode S

16 fJ

31 fJ

11 fJ
-2

10

1530 1531 1532

1567

1568

Wavelength (nm)

1569

-200

0

200

400

600

800

Time (ps)Fig. 2. Recorded switching operation of thesignal waveform as a function of the control
pulse energy.

Fig. 1. Electron microscope image of thesilicon PhC nanocavity (top). Linear
transmission spectrum (bottom).
- 46 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Nanoelectrode lithography
Atsushi Yokoo
Optical Science Laboratory
Recently, nanoprint-nanoimprint technologies or scanning probe microscope (SPM)
lithography is attracting attentions for the fabrication of nanostructures used in electronic or
optical devices. Compared to conventional "projection-type" lithography, these "contacttype" lithographies have advantages in size and ease of operation. However, because thebasic concept involves transferring the surface shape of a mold, the pattern cannot be
modified in nanoprint-nanoimprint technologies.
SPM lithography, in which an
electrochemical reaction is induced by a conductive probe tip, can provide pattern flexibility.
However, the throughput is still low. We are trying to develop a lithography technique thatcan provide good throughput and flexibility simultaneously.
Figure 1 shows the principle of nanoelectrode lithography. A nanoelectrode surface
consists of a conductive area and an insulating area. The nanoelectrode makes contact withthe surface of a target. When a voltage is applied, current flows between the nanoelectrodeand the target material. Then, an electrochemical reaction occurs on the target surface.
For example, anodic oxidation of the semiconductor, Si or GaAs, transfers the pattern to thetarget [1, 2]. Figure 2 shows an example of Si substrate patterning by nanoelectrodelithography. In Fig. 2, a nanoelectrode with a 300-nm-pitch dot pattern was used.
The
fabricated oxide pattern worked well as a mask for wet and dry etching, which means that
resist-less patterning is possible. In addition, nanoelectrode lithography does not deform thesurface of the target during the patterning process. Therefore, it will enable us to overwrite
a pattern to fabricate a more complex pattern. Figure 3 shows checked pattern fabricated byrepeating the process with a line-and-space (L/S) pattern [3].
As shown here, nanoelectrode lithography has some advantages, such as direct fabricationof the etching mask and modification of fabricated patterns by combining this approach withanother lithographic technique. In addition, the lithography process can directly fabricate
patterns defined by chemical characteristics such as hydrophilic or hydrophobic properties.
These pattern may be used as templates for selective growth of semiconductors. We will
apply nanoelectrode lithography for patterning of metal layers or resist layers on a substrate
to prove the generality of the technique.
[1] A. Yokoo, Jpn., J. Appl., Phys., 42, L92 (2003)[2] A. Yokoo, S. Sasaki, Jpn., J. Appl., Phys., 44, 1119 (2005)[3] A. Yokoo, J. Vac. Sci. Technol. B, 21, 2966 (2003)

Fig. 1 Nanoelectrodelithography

Fig. 3 Multiple patterning(a) after 1st procedure
Fig. 2 Fabricated pattern on Si(b) after 2nd procedure- 47 -

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Second NTT- Basic Research Laboratories School
Second NTT BRL School, under the theme of “Transport Properties in Quantum
Nanostructure”, was held during the period of October 8th to 14th, 2004 at Fuji Seminar House(Fujiyoshida city, Yamanashi prefecture) and NTT Atsugi R&D Center. The purpose was to1) foster young researchers in physics field and 2) improve visibility in international society.
Lectures were given by prestigious professors throughout the world: “Coulomb Blockadein Quantum Dots” by Prof. L. Glazman (University of Minnesota, USA), “Electronic
Properties of Semiconductor Nanostructures” by Prof. S. Tarucha (University of Tokyo,
Japan), “Quantum Dynamics of Superconducting Nanocircuits” by Prof. R. Fazio (Scuola
Normale Superiore, Italy), “Carbon Nanotubes (theory)” by Prof. C. Schönenberger(University of Basel, Switzerland), and “Carbon Nanotubes (experiment)” by Prof. T. Ando
(Tokyo Institute of Technology, Japan). Thirty two participants, mainly Ph.D. students,
gathered from diverse countries which counted up to 17.
Following the lectures, each student introduced his/her research overview in a poster style.
Director, managers and research group leaders of NTT BRL joined this session as well. In
response to the students’ detailed explanation of their research, vigorous discussion took place
among students, and between students and professors/NTT researchers, which continued until
the middle of the night.
Besides above mentioned schedule, the director presented overview of NTT BRL together
with its mission and system on the first day. On the last day, managers gave detailed
introduction of research activities at each laboratory, Materials Science Laboratory, PhysicalScience Laboratory and Optical Science Laboratory, followed by a laboratory tour to a cleanroom, low temperature laboratory, optical-materials evaluation equipment, andsuperconducting thin-film crystal-growth equipment.
At the end of the school, students were asked to fill out a questionnaire for overall
evaluation. The answers included: “extremely satisfying and highly concentrated lectures,”“became acquainted with the activities of NTT BRL and was impressed with its research
environment,” “became interested in working at NTT BRL in the future.” These favorable
responses indicate that the school provided great success in appealing quality of research
activities at NTT BRL and contributed to its visibility improvement. NTT BRL continuously
holds a school this year and will ongoingly engage in making further progress in raising its
profile among young researchers abroad.

- 49 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Science Plaza 2005
Science Plaza 2005, the annual open house event of NTT Basic Research Laboratories, washeld on January 24, 2005, at the NTT Atsugi R&D Center. Science Plaza 2005 was aimed not
only to introduce our latest research results to people inside and outside of NTT Basic
Research Laboratories, but also to provide us feedback and opinions through discussion.
During the Plaza, overviews of research activities in the fields of materials science,physical science, and optical science were presented in morning lectures. In the afternoon, Dr.
Mats Jonson, Professor of Physics at Chalmers University of Technology and Göteborg
University in Sweden, and a member of the Nobel Prize committee in Physics, presented a
special lecture entitled “The Nobel Prize in Physics, past, present and future”, reviewing thehistory of the Nobel Prize, the recent awards, and the outlook for the future.
In the Poster Session, we presented thirty of our latest research developments, which
generated lively debates and meaningful discussions among the participants. In addition, amovie highlighting our major research findings was shown in the video theatre. We performed
three Lab tours, which gave participants an opportunity to see the facilities used in NTT Basic
Research Laboratories, including the Low-Temperature Experiments Building, and learn how
our research is performed. After the program, we had a social gathering in the evening in thedining room, where participants could continue with their productive discussions.
Approximately, a total of 200 people from the research departments of universities,business organizations, and the NTT groups attended our Science Plaza 2005. The symposium
was a huge success. We would like to take this opportunity to sincerely thank all those who
participated in Science Plaza 2005.

Special lecture

Poster session

Lab tour: carbon nanotubes

Lab tour: low-temperaturephysical-property experiments- 50 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

The 3rd Advisory Board Meeting
The advisory board, an external evaluation committee for NTT Basic ResearchLaboratories (BRL), convened for three days, January 25, 26, and 27, 2005. The advisoryboard started in 2001 as a way to evaluate research plans and activities objectively so thatNTT BRL can adopt strategic management in a timely manner. This was the third board
meeting, and this time we reorganized the board to welcome five new members.
During the meeting, the board gave us many valuable suggestions and comments on our
research activities and management. Members commented that the research level is generallyhigh on a world scale, which strengthened our commitment to keep our research at the top
level and communicate our results and ideas to the world. They also pointed out several issues
regarding human resources, inheritance of technology, and internal and external collaboration.
We will work to improve our management and circumstances based on their valuablesuggestions.
At this meeting, there were many opportunities for young researchers to communicate
with the board members. We had a lunch party and also conducted laboratory tours withyoung researchers as attendants. The board members and young researchers enjoyed thesechances to interact. The next board meeting will convene in a year and half.

Board members
Affiliation
Prof. Altshuler
Princeton U
Prof. Devoret
Yale U
Prof. Haroche
Ecole Normale
Prof. Jonson
Chalmers UTProf. Leggett
U Illinois
Prof. Mooij
Delft UT
Prof. Ploog
Paul-Drude-Inst.
Prof. RyanU Oxford
Prof. von Klitzing Max-Planck-Inst.

Research field
Condensed matter
Mesoscopic physics
Quantum optics
Condensed matter
Quantum physics
Quantum computers
Nanostructures
Nano-bio technology
Semiconductor physics- 51 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

International Conference on
Nanoelectronics, Nanostructures and Carrier Interactions
The conference was held from January 31 to February 2, 2005, at the NTT Atsugi R&D
Center in collaboration with Solution Oriented Research for Science and Technology(SORST) sponsored by the Japan Science and Technology Agency (JST).
Ultra-small “nano-scale” structures and the behavior of carriers in these structures havebeen the focus of much attention for many years. Recently, the field has been advanced
significantly through the introduction of additional degrees of freedom, such as electron andnuclear spins, magnetism, and mechanical motion. In addition, novel quantum mechanicalconcepts like quantum computing and quantum cryptography are attracting a great deal ofinterest. With the aim of further advancing these studies, this conference aspired to gather
leading scientists and provide forum for discussing the most recent topics in nanoelectronics,
nanostructures, and carrier interactions. The conference was organized by Dr. Yoshiro
Hirayama and Dr. Hiroshi Yamaguchi of NTT Basic Research Laboratories which have ledthese fields.
On January 31st, after the opening and welcoming remarks by Dr. Hideaki Takayanagi,
Director of NTT Basic Research Laboratories, the technical session was opened with theinvited talk “Superconducting Flux Qubits” by Prof. J. E. Mooij from Delft University ofTechnology. There were 11 oral presentations on superconducting q-bits, nanoprobes, andmesoscopic/spin phenomena, and 28 poster presentations. On February 1st, the 12 oralpresentations discussed micro/nanomechanical systems, quantum information processing, andmesoscopic and spin phenomena. On the 2nd, there were 9 oral presentations on nuclear spin
and related phenomena and advanced heterostructures, and 28 poster presentations. The final
talk was given by Prof. K. Ploog from Paul Drude Institute on “Unexpected Gems in the
Search for Optimized Spin-Injector Materials”. We believe that we provided a very niceopportunity for mutual communication within and among the related research fields.
The participants were totally 149 people [including 67 from NTT]. All participants wellenjoyed the high-quality presentations and discussions on nanoelectronics, nanostructures,and carrier interactions.

- 52 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Award Winner’s List (Fiscal 2004)

Japanese Journal ofApplied Physics
Research Paper
Presentation Awards

S. Saito“Multiphoton Absorption Observedin a Superconducting Flux Qubit”

May 17,2004

The 33rd IEEE
International
Symposium on
Multiple-Valued Logic
Distinctive Contributed
Paper Award

H.Inokawa
Y.Takahasi"Experimental and Simulation Studies
of Single-Electron-Transistor-BasedMultiple-Valued Logic"

May 21,
2004“Development of Molecular Beam
Epitaxy for High Tc
Superconducting Materials”

June 21,2004

The Society of
Non-Traditional
M. NaitoTechnology Award forSuperconductor scienceand technology

Japanese Journal ofApplied Physics Paper
Award

V. Seleznev
H. Yamaguchi
Y. Hirayama
V. Y. Prinz“Single. Turn GaAs/InAs Nanotubes
Fabricated Using the Supercritical
CO2 Drying
Technique”

Sep. 1,
2004

Japanese Journal ofApplied Physics Paper
Award

T. Nishikawa
K. Oguri
T. Suzuki
Y. Watanabe
H. Nakano“Enhanced Water-Window X-Ray
Pulse Generation from Femtosecond
Laser Produced Plasma with a
Carbon Nanotube Target”

Sep. 1,
2004

Fellow of The Instituteof Physics (IOP)

Y. Hirayama“Contribution to the institute as amember of an Editorial Board”

Sep. 1,2004- 53 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

The Ericsson Young
Scientist Award

Physical Society of
Japan
JPSJ Editor’s Choice
Paper

Japan Society for the
Promotion of Science
Prize

Go Yusa“Trappingofphotogenerated
carriers by InAs quantum dots andpersistent photoconductivity innovel GaAs/n-AlGaAs field-effecttransistor”

Nov. 22,
2004

M. Kawamura
H. Yaguchi
N. Kikugawa
Y. Maeno
H. Takayanagi“Tunneling Properties at the Interface
between Superconducting Sr2RuO4 and a Ru
Microinclusion”

Feb. 1,
2005

T. Fujisawa“Research on Quantum-state Control
of Semiconductor
Quantum Dots”

Mar. 22,2005- 54 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

In-house Award Winner’s List (Fiscal 2004)

NTT R&D Award

T. Hayashi
T. Fujisawa“Electronically Controlled
Semi-conductor Qbits”

Dec. 8,2004

NTT R&D AwardK. Yamazaki
H. Namatsu“Nano-Globe”

Dec. 8,
2004

Award forAchievements by
Director of Basic
Research
Laboratories

H. Yamaguchi“Pioneering in Quantum
Nano-mechanics”

Mar. 15,
2005

Award forAchievements by
Director of Basic
Research
Laboratories

H. Tanaka
S. Saito
M. UedaH. Nakano
K. Semba“Coherent Control on Superconducting Mar. 15,
Flux Qbits”
2005

Award forAchievements by
Director of Basic
Research
Laboratories

T. Honjo
H. Takesue
K. Inoue
Y. Tokura“Quantum Key Distribution and Entangled Mar. 15,
Photon Generation with Optical Fibers”
2005

K. Takashina“Valley splitting control in SiO2/Si/SiO2
quantum wells in the quantum Hall Mar. 15,
regime” Phys. Rev. B Vol. 69, 161304(R) 2005
(2004)

T. Akasaka“An InGaN-based horizontal cavity
surface emitting laser diode” Appl.
Phys. Lett. Vol. 84, 4104 (2004)

Award for
Excellent Papers by
Director of Basic
Research
Laboratories
Award for
Excellent Papers by
Director of Basic
Research
Laboratories- 55 -

Mar. 15,2005

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Special Award by
Director of Basic
Research
Laboratories

Award forAchievements by
Director of Photonics
Laboratories

H. Namatsu

H.Yokoyama
M. Hiroki
H. Sugiyama
K. Kumakura
N. Watanabe“Distinctive Contribution on Patent
Application”

Mar. 15,2005“Development of Fabrication TechniquesMar. 16,for High Quality GaN/AlGaN HEMT
2005
Epitaxial Wafers on Sapphire Templates”- 56 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

List of Visitor’s Talks (Fiscal 2004)
l. Materials Science
Date

Speaker

May 17 Mr. Atsushi Nishikawa

June 1

Prof. I.S.T. Tsong

June 11

Dr. Jingyue Liu

June 18 Dr. Jun Nakamura

July 6

Dr. Sonia A. Contera

Nov. 15 Prof. Daoben Zhu

Nov. 15 Prof. Wenping Hu
Nov. 22 Prof. Esko I. Kauppinen

Feb. 17 Prof. Clive BramhamFeb. 22 Prof. Mervyn Miles

Feb. 22 Prof. Daniel RobertMar. 10 Prof. Kenshi Hayashi

Affiliation"Topic"The University of Tokyo“Fabrication of GaInNAsQuantum Dots by MBE
and Its Optical Characterization”
Arizona State University, USA“Nucleation and growth of epitaxial ZrB2(0001) on
Si(111) for III-nitride applications”
Monsanto Company, USA“Electron Microscopy of Atoms and Clusters”
The University of Electrto-Communications“Dielectric characteristic evaluation of ultra-thinfilm by first-principle calculation”
University of Oxford, UK“Pulling an alpha-helix peptide out of a lipid bilayer
with an AFM”
Chinese Academy of Sciences, China“Recent Advance on Molecular Materials in
the Organic Solid Laboratory”
Chinese Academy of Sciences, China“Self Assembly Devices”
Helsinki University of Techology, Finland“Nanoparticle Technology Center for New Materials(CNM)”
University of Bergen, Norway“Molecular mechanisms of synaptic plasticity invivo: BDNF as a trigger for synaptic consolidation”
University of Bristol, UK“Real-time imaging of materials using fast scan
AFM”
University of Bristol, UK“Mechano receptor involvement in nanoscalesensing capability of insect antennae”
Kyushu University“Multi-purpose electrochemical sensor detecting
molecular adsorption”- 57 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

lI. Physical Science
Date

Speaker

Affiliation"Topic"Apr. 7

Prof. T. Claeson

Apr. 15

Prof. Yosuke Kayanuma

Apr. 28

Prof. Fujio Shimizu

May 19Prof. Kees Harmans

May 25

Dr. Gunther Lientschnig

July 16

Dr. Cary Y. Yang

Sep. 7

Dr. Evgeni Ilichev

Sep. 10

Dr. P. V. Santos

Sep. 14

Prof. R. A. Hogg

Sep. 16

Prof. Hideo Kosaka

Oct. 6

Prof. Susumu Sasaki

Oct. 6

Prof. Ruldof Gross

Oct. 14

Dr. Ch. vom Hagen

Chalmers University of Technology, Sweden“Transport in single molecules: influence ofdistinctly different charged states of the conjugate
molecule and of the image charge in theelectrodes”
Osaka Prefecture University“Nonadiabatic Electron Manipulation in a
Quantum-Dots Array and Some Related Topics”
University of Electro-Communications“How to pursue atomic quantum computer”
Delft University of Technology, Netherlands“Quantum dynamics of persistent current Qubits”
Delft University of Technology, Netherlands“Electrical Transport through Molecules”
Santa Clara University, USA“Carbon Nanotubes as On-chip Interconnects”
Jena University, Germany“Radio-frequency method for investigation ofquantum properties of superconducting structures”
Paul Drude Institute, Germany“Controlling photons,electrons, and spins in GaAs
using acoustic waves”
University of Sheffield, UK“Low Threshold 1.31um QD laser Diodes on GaAs”
Tohoku University“Qbits Conversion from Polarization of Photons toElectron Spin”
Niigata University“A new development of neuclear magnetic
resonance (NMR): Coherence of neuclear spins insemiconductors”
Bavarian Academy of Sciences, Germany“Research activity in Solid state based quantum
information, within the Cooperative ResearchCenter 6317”
Universitat Heidelberg, Germany- 58 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Nov. 2

Prof. A.D. Zaikin

Nov. 18

Prof. Eugene S. Polzik

Nov. 19

Prof. Gerhald Abstreiter

Dec. 1

Prof. V. Y Prinz

Dec. 2

Prof. Pawel Hawrylak

Dec. 3

Prof. A. J. Fisher

Dec. 16

Prof. Miles.P.Blencowe

Dec. 16

Prof. K. H. Ploog

Dec. 22

Dr. Vladimir Bubanja

Jan. 11

Dr. Pablo Jarillo-HerreroJan. 19

Prof. Jung-Bum Choi

Feb. 21

Dr. Alexander Khaetskii

Feb. 25

Prof. Tetsuya SatoFeb. 25

Vittorio Peano
Michael Thorwart“Towards a Degenerate Fermi Gas on an Atom
Chip”
Universitat Karlsruhe, Germany“Interaction-induced low temperature decoherenceof electrons in disordered conductors: Theory andExperiment”
Copenhagen University, Denmark“Quantum memory for light: can complementary
variables be remembered?”
Walter Schottky Institute, Germany“Optoelectronic control of single charge, spin andphoton in semiconductor quantum dots and its
possible impact on future quantum information
technology”
Russian Academy of Science, Russia“Precise semiconductor nanotubes,nanofibers andnanocorrugated quantum systems”
National Research Council of Canada, Canada“Designing quantum systems for nano-spintronics,
nano-photonics
andquantum
information
processing”
University College London, UK“Decoherence and quantum information processing
in condensed matter”
Dartmouth College, USA“Mesoscopic Mechanics”
Paul Drude Institute, Germany“Nitrides seem to be good for everything”
Industrial Research, New Zeeland“Single Electron Metrology”
Delft University of Technology, Netherlands“Orbital spectroscopy and Kondo effects incarbonnanotubes”
Chungbuk National University, Korea“Single-Electronics: Beyond the Roadmap CMOS
toward Quantum Computation”
Russian Academy of Science, Russia“Spin currents. Myth and reality.”
Keio University“Magnetic Properties in Surfaces of Nano Particles”
Dusseldorf University, Germany“One-Dimensional Ultracold Atom Gases in a
Nanoscale Magnetic Waveguide formed by two- 59 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Mar. 15

Prof. Bernhard Kramer

Mar. 18

Prof. Jörg Schmiedmayer

Mar. 22

Mr. Anton ÖttlDoubly-Clamped Suspended Carbon NanoTubes”
Universtitaet Hamburg, Germany“Spin blockade in quantum dots”
Universität Heidelberg, Germany“Micro-manipulation of ultra cold atoms on Atom
Chips”ETH Zürich, Switzerland“Observation of Single Atoms in Degenerate
Quantum Gases”

lII. Optical Science
Date

Speaker

Affiliation"Topic"The University of Tokyo“Properties of Quasi-crystals: Current State andFuture Prospects”
SUNY Buffalo, USA“Dynamical Nuclear Spin Polarization in a
Semiconductor Double Quantum Dots”
The University of Illinois, USA“Photonic Crystal VCSEL (Vertical Cavity Surface
Emitting Laser)”
General Physics Institute, Russia“Waveguide-plasmon polaritons in photonic crystal
slabs with metal nanowires”
TU Berlin, Germany“Semiconductor Nano Optics: Perspective from the
Theory of Light-Matter Interactions on Ultrashort
Time and Length Scales”
TU Berlin, Germany“Ultrafast Optics of Multiple-Quantum-Well
Photonic Crystals”
Ben-Gurion University, Israel“Fano effect of a strongly interacting quantum dot in
contact with superconductor”
University of Oxford, UK“The Photon and the Vacuum Cleaner”

Apr.

16

Prof. Keiichi Edagawa

July

7

Dr. Xuedong Hu

Aug. 19

Mr. Aaron Danner

Sep.

22

Prof. S. G. Tikhodeev

Nov.

11

Prof. A. Knorr

Nov.

17

Prof. A. Knorr

Jan.

7

Prof. Yshai Avishai

Mar.

11

Prof. Ian Walmsley- 60 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Research Activities of Basic Research Laboratories in 2004
The numbers of research papers, presentations at the international conferences and applied
patents amounted to 227, 196, and 64 in Basic Research Laboratories as a whole. All numbers
according their research areas are as follows.

Research Papers Published in International Journals(2004.1 - 2004.12)

Material Science

Physical Science

Optical Science

0

20

40

60

80

100

120

100

120

40

50

Number of Papers

Presentations at International Conferences(2004.1 - 2004.12)
Material Science
Physical Science
Optical Science
0

20

40

60

80

Number of Presentations

Applied Patents (2004.1 - 2004.12)
Material Science
Physical Science
Optical Science
0

10

20

30

Applied Patents
Domestic- 61 -

International

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

The major journals and the number of published papers are shown below.
General Science Journals
Name
NatureSpecialized Journals
Name
Physica E
Japanese Journal of Applied Physics
Physical Review B
Applied Physics Letters
Physica C
Physical Review Letters
Applied Surface Science
Nano Letters
Advanced Materials
Analytical Chemistry
Biophysical Journal(IF2003)*(30.979)

Numbers
1(IF2003)*(0.93)(1.171)(2.962)(4.049)(1.192)(7.035)(1.284)(6.144)(7.305)(5.25)(4.463)

Numbers
34
32
24
23
13
12
7
2
1
1
1

*IF2003: Impact factor 2003 （Journal Citation Reports, 2003）

The average impact factor for individual research papers from all NTT Basic ResearchLaboratories is 2.42.
The major international conferences and their number of presentation are shown below.
Conferences

Numbers

27th International Conference on the Physics of Semiconductors(ICPS27)

17

International Symposium on Mesoscopic Superconductivity andSpintronics 2004
International Conference on Solid State Devices and Materials (SSDM)
Annual APS March Meeting 2004
MRS Meeting 2004
CLEO/QELS 2004
14th International Conference on Ultrafast Phenomena
17th International Symposium on Superconductivity (ISS2004)
2004 International Workshop on Dielectric Thin Films for Future ULSI
DevicesInternational Workshop on Nitride Semiconductors- 62 -

12
11
7
7
4
4
4
4
4

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

List of Invited Talks at International Conferences (2004)
I. Material Science Laboratory(1) N. Kobayashi, K. Kumakura, T. Makimoto, T. Hashizume, T. Fukui, and H. Hasegawa,“Characterization of Heterojunction in High Current Gain GaN/InGaN Heterojunction Bipolar
Transistors”, 31st Conference on The Physics and Chemistry of Semiconductor Interfaces(PCSI-31), Hawaii, USA (Jan. 2004).
(2) T. Nishida, T. Ban, H. Saito, N. Kobayashi and T. Makimoto, “High power extraction of 340 to
350-nm UV-LEDs”, Photonics West, San Jose, USA (Jan. 2004).
(2) K. Furukawa, “Single polymer science based on semiconducting polymer”, International
Workshop “Beam Science and Nanotechnology”, Osaka, Japan (Jan. 2004).
(4) Y. Homma, Y. Kobayashi, J. Lefebvre, and P. Finnie, “Suspended Carbon Nanotube
Architectures: Growth Control and Optical Properties”, International Symposium on theCreation of Novel Nanomaterials (ISCNN'04)”, Toyonaka, Japan (Jan. 2004)(5) E. Kohn, A. Aleksov, M. Kubovic, A. Denisenko, and M. Kasu, “Diamond electronic devices opportunities and obstacles”, 9th International Conference on New Diamond Science andTechnology, Tokyo, Japan (Mar. 2004).
(6) Y. Homma, “Standardization of SIMS depth profiling in ultra-shallow region”, 1st International
Symposium on Standard Materials and Metrology for Nanotecnology (SMAM-1), Tokyo, Japan(Mar. 2004)(7) K. Torimitsu, “Nano-bio science: from molecule to nano-bio device”, Chinese Chemical Society& 24th CCS Congress, Hunan, China (Apr. 2004).
(8) K. Torimitsu, N. Kasai and Y. Furukawa, “Effect of magnesium on neural ativities in cultured
rat cortical and hippocampal neurons”, 8th European Magnesium Conf., Romania, Italy (May,2004).
(9) C. Han and K. Torimitsu, “Neuronal cell death and sprouting of mossy fibers are induced bykanic acid exposure in rat hippocampal slice cultures”, The 3ed International Symposium on
Neuroscience of Young Scholars”, Guangzhou, China (Jun. 2004).
(10) Y. Homma, “Towards standardization of ultra-shallow depth profiling:- 63 -

Multiple delta layers

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

as a measure of depth scale”, 16th International Vacuum Congress, Venice, Italy (Jun. 2004)(11) K. Torimitsu, “Bioinfomatics”, The 19th UK-Japan High Technology Industry Forum, Bristol,
UK (Jul. 2004).
(12) K. Torimitsu, Y. Furukawa, H. Nakashima, K. Furukawa, Y. Kashimura and W. Hu, “NanoBio
Science - Neural functions and molecules”, ICCE-11, Hilton Head Island, USA (Aug. 2004).
(13) T. Makimoto and K. Kumakura, “Recent Development of Nitride Heterojunction Bipolar
Transistors”, 2004 ECS Joint Meeting in Hawaii, Honolulu, USA (Oct. 2004).
(14) Y. Watanabe, S. Suzuki, Y. Homma, S. Heun, and A. Locatelli, “SPELEEM observation ofindividual single-walled carbon nanotubes”, 3rd Int. Workshop on Nanoscale Spectrosc.
Nanotech., Maryland, USA (Dec. 2004).

II. Physical Science Laboratory(1) T. Fujisawa “Coherent control of carrier dynamics in coupled quantum dots”, 31st Conf. Phys.
Chem. Semicond. Interface (PCSI-31), Kailua-Kona, USA (Jan. 2004).
(2) T. Fujisawa “Dynamics of single-electron charge in quantum dots”, 20th Yokohama City
University International Forum (YCUIF-20), Yokohama, Japan (Jan. 2004).
(3) T. Hayashi, T. Fujisawa, and Y. Hirayama, “Coherent charge oscillation and decoherence in asemiconductor double quantum dots”, Rencontres de Moriond, La Thuile, Italy (Jan. 2004).
(4) H. Takayanagi, “Superconducting Flux Qubit as a Macroscopic Artificial Atom”, 39th Recontres
de Moriond, LaThuile, Italy (Jan. 2004).
(5) Y. Tokura, “Spin-Effects in a Transport Through a Point Contact”, Int. Workshop on Spin-FET
based Quantum Information Processing, Tsukuba, Japan (Feb. 2004).
(6) K. Inoue, “Nonlinear amplifiers and fiber processing devices,” Conference on Optical Fiber
Communications (OFC2004), Los Angles, USA (Feb. 2004).
(7) H. Tamura, “Tunable exchange interaction and Kondo screening in quantum dot devices”, The
2nd Quantum Transport Nano-Hana International Workshop, Chiba, Japan (Mar. 2004)(8) H. Takayanagi, “Quantum Information Processing at NTT BRL”, International Symposium on- 64 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Quantum Info-Communications and Related Quantum Nanodevices, Tokyo, Japan (Mar. 2004).
(9) H. Takayanagi, “Superconducting Flux Qubit”, Quantum Technologies 2004, Vancouver,
Canada (Mar. 2004).
(10) T. Fujisawa “Dynamics of single-electron charge in quantum dots”, Material Research Society(MRS) Meeting, San Fransisco, USA (Apr. 2004).
(11) K. Semba, “Superconducting qubits:Experimental forefront and challenges”, International
conference : Are the DiVincenzo Criteria fulfilled 2004 ?, Osaka, Japan (May. 2004).
(12) J. Nitta, “Spin-related transport in semiconductors and semiconductor/ferromagnet hybrid
structures” International Conference on “Nanospintronics Design and Realization” ICNDR,
Kyoto, Japan, (May 2004)(13) T. Fujisawa, “Dynamics of Single Electron Charge in a Double Quantum Dot”, Quantum Dots
Conference (QD2004), Alberta, Canada (May, 2004).
(14) T. Fujisawa “Dynamics of single-electron charge and spin in semiconductor quantum dots”,
Quantum Computation:Are the DiVincenzo criteria fulfilled in 2004?, Osaka (May 2004).
(15) Y. Hirayama, “Coupled-quantum-dot charge qubit”, Spin and Qubit, Niels Bohr Institute,
Copenhagen, Denmark (May, 2004).
(16) Y. Hirayama, T. Hayashi, T. Fujisawa, “Semiconductor charge qubit”, ITAMP workshop on
Mesoscopic Physics, Quantum Optics, and Quantum Information, Boston, USA (May, 2004).
(17) H. Inokawa, Y. Ono, A. Fujiwara, K. Nishiguchi, and Y. Takahashi, “Single-Electron Devices
fabricated by MOS Processes,” European Materials Research Society (E-MRS) Spring Meeting,Strasbourg, France (May, 2004).
(18) H. Takayanagi, “Research Acitivities of Quantum Information Technology at NTT BRL”, Spin
Qubit Symposium, Copenhagen, Denmark (May 2004)(19) T. Fujisawa “Dynamics of single-electron charge and spin in semiconductor quantum dots”,
International workshop on Macroscopic Quantum Coherence and Computing (MQC2), Napoli,
Italy (Jun. 2004).
(20) S. Horiguchi, A. Fujiwara, H.Inokawa and Y. Takahashi, “Electronic States in Si- 65 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Single-Electron Transistors,” IEEE Si Nanoelectronics Workshop, Honolulu, USA (Jun. 2004).
(21) Y. Takahashi, Y. Ono, A. Fujiwara, K. Nishiguchi, and H. Inokawa, “Fabrication andApplication of Silicon Single-Electron Devices,” Ultimate Lithography and Nanodevice
Engineering Conference, Agelonde, France, (Jun. 2004).
(22) H. Takayanagi, “Superconducting Flux Qubit”, Foundation of Probability and Physics-3, Växjӧ,
Sweden (June 2004)(23) M. Yamashita, “Magnetic properties of trapped spin-one bosons in an optical lattice”,
International Laser Physics Workshop (LPHYS'04), Trieste Italy (Jul. 2004).
(24) T. Fujisawa, “Single electron charge qubit in a semiconductor double quantum dot”, Control ofquantum coherence, BadHonnef, Germany(Jul. 2004).
(25) Y. Hirayama, “Manipulation of nuclear spin polarization and relaxation by two-dimensional
electron systems”, International Conference on Superlattices, Nano-structures and Nano-devices(icsnn04), Cancun, Mexico (Jul. 2004).
(26) H. Yamaguchi, S. Miyashita, Y. Tokura, and Y. Hirayama “InAs-based MicromechanicalTwo-dimensional Electron Gas Systems”, 27th International Conference on the Physics of
Semiconductors (ICPS27), Flagstaff, USA (July. 2004).
(27) M. Uematsu, “Unified simulation of diffusion in silicon and silicon dioxide,” 6th international
conference on diffusion in materials (DIMAT), Krakow, Poland (Jul. 2004).
(28) J. Nitta, “Spin-controlled transport in semiconductor nano-structures” Taiwan International
Conference on Superconductivity and Low Temperature Physics, Penghu, Taiwan (Jul. 2004)(29) H. Yamaguchi, “Quantum Micro/Nanomechanical Systems”, JAIST International Symposium
on Nano Technology 2004 (NT2004), Ishikawa, Japan (Sept. 2004).
(30) J. Nitta, “Challenges of Spintronics; from basics to nanoscale devices”, Ramp Sessions
Panelist, International Conference on Solid State Devices and Materials (SSDM 2004), Tokyo,
Japan (Sep. 2004)(31) J. Nitta, “Spin controlled transport in semiconductor nano-structures andsemiconductor/ferromagnet hybrid structures”, The 7th Oxford-Kobe Materials Seminar;
Spintronics Materials and Technology, Kobe Institute, Kobe (Sep. 2004)- 66 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)(32) T. Fujisawa, “Quantum information devices based on semiconductor quantum dots”, Solid
State Devices and Materials, Tokyo, Japan (2004).
(33) T. Fujisawa, “Dynamics of single-electron charge and spin in semiconductor quantum dots”,
ERATO Imai Quantum Information Science (EQIS) Workshop, Tokyo, Japan (Sep. 2004)(34) Y. Hirayama, “Experimental Implementation of Semiconductor Qubit”, Isaac Newton Institute,Cambridge, UK (Sep. 2004).
(35) H. Yamaguchi, S. Miyashita, and Y. Hirayama, “Force/Displacement Detection using Quantum
Effects in InAs/Al0.5Ga0.5Sb Two-dimensional Electron Systems”, 2004 International
Symposium on Compound Semiconductors (ISCS2004), Soul, Korea (Sept. 2004).
(36) H. Takayanagi, “Solid State Qubits”, Solid State Based Quantum Information Processing,
Herrsching, Germany (Sep. 2004)(37) F. Shimizu “New Quantum Mechanical Applications of Atoms”, The 9th Asia Pacific Physics
Conference (9th APPC), Hanoi, Vietnam (Oct. 2004).
(38) Y. Hirayama, “Manipulation of Nuclear Spins in GaAs Based Hetero- and Nanostructures”,
Frontiers in Nanoscale Science and Technology, Boston, USA (Oct. 2004).
(39) T. Fujisawa, “Dynamics of single-electron charge and spin in semiconductor quantum dots”,
Tera-level Nano-Devices (TND) Workshop, Seoul, Korea (Oct. 8, 2004).
(40) Y. Takahashi, Y. Ono, A. Fujiwara, and H. Inokawa, “Silicon Single-Electron Devices andTheir Applications,” The 7th International Conference on Solid-State and Integrated-Circuit
Technology (ICSICT), Beijing, China (Oct. 2004).
(41) Y. Takahashi, Y. Ono, A. Fujiwara, K. Nishiguchi, and H. Inokawa, “Application of SiliconSingle-Electron Devices,” First Annual Meeting on the Fusion of Biotechnology,
Nanotechnology and Semiconductor Technology (FBNS), Kyoto, Japan (Oct. 2004).
(42) H. Takayanagi, “Readout of Superconducting Flux Qubits”, The 4th Taiwan-Japan
Microelectronics International Symposium -Nano, MEMS/NEMS, and Display Technologies-,
Hsinchu, Taiwan (Oct. 2004)(43) H. Takayanagi,”RKKY Interaction on Quantum Dot Array”,
Nanoscale Physics, Argonne, USA (Nov. 2004)- 67 -

Argonne Fall Workshop on theResearch Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)(44) H. Takayanagi, “Readout of Flux Qubit”, Processing of Quantum Information in RSFQ
Circuits and Qubits”, Bad Honnef, Germany (Nov. 2004)(45) K. Semba “Coherent control of superconducting flux qubits”, 17th International Symposiumon Superconductivity (ISS2004), Niigata, Japan (Nov. 2004).
(46) T. Fujisawa, “Dynamics of single-electron charge and spin in semiconductor quantum dots”,
The 1st Asia-Pacific Conference on QIS, Tainan, Taiwan (Dec., 2004).
(47) Y. Takahashi, Y. Ono, A. Fujiwara, K. Nishiguchi, and H. Inokawa, “Single-Electron Device
applications using their special functionalities,” The 6th International Conference on
Nano-molecular Electronics (ICNME-2004), Kobe, Japan (Dec. 2004).
(48) K. Semba “Coherent control of superconducting flux qubit”, Joint Workshop on
Superconductivity The Second CREST-NANOFAB Workshop NFS2004 The XII-th Vortex
Physics Workshop of Japan (VPJ12) Osaka, Japan (Dec. 2004).

III. Optical Science Laboratory(1) H. Nakano, K. Oguri, and T. Nishikawa, “Temporal characterization of femtosecond soft x-ray
pulse using optical field-induced ionization dynamics in noble gas,” The Fourth Asian Pacific
Laser Symposium (APLS 2004), Yongpyong, Korea (Mar. 2004).
(2) M. Notomi, H. Suzuki, T. Tamamura, K. Edagawa, “Penrose-lattice laser: lasing action due toquasi-periodicity”, International Workshop on Photonic Electromagnetic Structures (PECS-V),
Kyoto, Japan (Mar. 2004).
(3) M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H-Y. Ryu, S. Hughes, G-H. Kim, T. Tanabe,“Multi-Port PBG Components in SOI Photonic Crystal Slabs”, OSA Topical Meeting ofIntegrated Photonic Research (IPR 2004), San Francisco, USA (Jun. 2004).
(4) M. Notomi, “PBG Waveguides and Related Devices in SOI Photonic Crystal Slabs”, OECC
Workshop for Micro/Nano Waveguides and Devices, Yokohama, Japan (Jul. 2004).
(5) M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H-Y. Ryu, S. Hughes, G-H. Kim, T. Tanabe,“Light Propagation Control in Photonic Crystals: Dispersion and Confinement”, OSA Topical
Meeting of Ultrafast Phenomena (UP2004), Niigata, Japan (Jul. 2004).

- 68 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)(6) S Hughes, “Optical Scattering and Single-Quantum-Dot Strong Coupling in Semiconductor
Photonic Crystal Slabs,”
Colorado Meeting on Fundamental Optical Processes in
Semiconductors (FOPS), Colorado, USA (Aug. 2004).
(7) M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H-Y. Ryu, G-H. Kim, T. Tanabe, “Slow-light
Waveguides and High-Q Nano-resonators in Photonic Crystals”, Frontiers in Optics, OSA
Annual Meeting (FiO 2004), Rochester, USA (Oct. 2004).
(8) M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H-Y. Ryu, S. Hughes, G-H. Kim, T. Tanabe,“PBG Resonators and Waveguides in SOI Photonic Crystals”, International Conference on
Solid-State Devices and Materials (SSDM 2004), Tokyo, Japan (Sep. 2004).
(9) H. Nakano, K. Oguri, and T. Nishikawa, “Bright ultrafast EUV sources for time-resolved
absorption measurements,” The 17th Annual Meeting of the IEEE Lasers & Electro-Optics
Society (LEOS 2004), Rio Grande, Puerto Rico (Nov. 2004).
(10) A. Yokoo, “Photonic crystal with organic functional material”, The 4th International
mini-Symposium on Advanced Organics Photonics (ISAOP-4), Osaka, Japan (Nov. 2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

List of Research Papers Published in International Journals

Material Science LaboratoryThin-Film Materials Research Group1.

T. Akasaka, H. Gotoh, T. Saito, and T. Makimoto, "High luminescent efficiency of
InGaN multiple quantum wells grown on InGaN underlying layers," Appl. Phys. Lett.
85 (15), 3089-3091 (2004).

2.

T. Akasaka, T. Nishida, T. Makimoto, and N. Kobayashi, "An InGaN-based
horizontal-cavity surface-emitting laser diode," Appl. Phys. Lett. 84 (20), 4104-4106(2004).

3.

A. Aleksov, M. Kubovic, M. Kasu, P. Schmid, D. Grobe, S. Ertl, M. Schreck, B.
Stritzker, and E. Kohn, "Diamond-based electronics for RF applications," Diam. Relat.
Mat. 13 (2), 233-240 (2004).

4.

B. Chesca, K. Ehrhardt, M. Mossle, R. Straub, D. Koelle, R. Kleiner, and A. Tsukada,"Phase-sensitive evidence for a predominant d-wave pairing symmetry in the electron
doped superconductor La2-xCexCuO4-y," Physica C 408-10, 321-323 (2004).

5.

T. Fujii, I. Terasaki, and A. Matsuda, "Thermopower anisotropy of lightly-doped andoptimally-doped Bi2Sr2-xLaxCaCu2O8+delta single crystals," Physica C 408-10,
674-676 (2004).

6.

T. Hashizume, S. Anantathanasarn, N. Negoro, E. Sano, H. Hasegawa, K. Kumakura,and T. Makimoto, "Al2O3 insulated-gate structure for AlGaN/GaN heterostructure
field effect transistors having thin AlGaN barrier layers," Jpn. J. Appl. Phys. Part 2 Lett. Express Lett. 43 (6B), L777-L779 (2004).

7.

M. Hiroki, K. Kumakura, T. Makimoto, N. Kobayashi, and T. Kobayashi,"Fabrication of GaN/Alumina/GaN structure to reduce dislocations in GaN," Jpn. J.
Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (4B), 1930-1933 (2004).

8.

S. Karimoto and M. Naito, "Electron-doped infinite-layer thin films with T-C over 40
K grown on DyScO3 substrates," Appl. Phys. Lett. 84 (12), 2136-2138 (2004).

9.

S. Karimoto and M. Naito, "Electron-doped infinite-layer thin films with
T-C(zero)=41 K grown on DyScO3 substrate," Physica C 412-14, 1349-1353 (2004).

10.

M. Kasu, M. Kubovic, A. Aleksov, N. Teofilov, R. Sauer, E. Kohn, and T. Makimoto,"Properties of (111) diamond homoepitaxial layer and its application to field-effecttransistor," Jpn. J. Appl. Phys. Part 2 - Lett. Express Lett. 43 (7B), L975-L977 (2004).

11.

M. Kasu, M. Kubovic, A. Aleksov, N. Teofilov, Y. Taniyasu, R. Sauer, E. Kohn, T.
Makimoto, and N. Kobayashi, "Influence of epitaxy on the surface conduction of
diamond film," Diam. Relat. Mat. 13 (2), 226-232 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

12.

A. Kubovic, A. Denisenko, W. Ebert, M. Kasu, I. Kallfass, and E. Kohn, "Electronic
surface barrier characteristics of H-terminated and surface conductive diamond,"
Diam. Relat. Mat. 13 (4-8), 755-760 (2004).

13.

M. Kubovic, M. Kasu, I. Kallfass, M. Neuburger, A. Aleksov, G. Koley, M. G.
Spencer, and E. Kohn, "Microwave performance evaluation of diamond surface
channel FETs," Diam. Relat. Mat. 13 (4-8), 802-807 (2004).

14.

J. Kurian and M. Naito, "Growth of epitaxial CeO2 thin films on r-cut sapphire bymolecular beam epitaxy," Physica C 402 (1-2), 31-37 (2004).

15.

J. Kurian and M. Naito, "Low microwave surface resistance in NdBa2Cu3O7-delta
films grown by molecular beam epitaxy," Jpn. J. Appl. Phys. Part 2 - Lett. Express
Lett. 43 (11B), L1502-L1505 (2004).

16.

J. Kurian, M. Naito, H. Sato, and K. Cho, "Large area RE-123 thin films for
microwave applications grown by molecular beam epitaxy," Physica C 412-14,
1513-1518 (2004).

17.

T. Makimoto, K. Kumakura, and N. Kobayashi, "Extrinsic base regrowth of p-InGaN
for Npn-type GaN/InGaN heterojunction bipolar transistors," Jpn. J. Appl. Phys. Part
1 - Regul. Pap. Short Notes Rev. Pap. 43 (4B), 1922-1924 (2004).

18.

T. Makimoto, Y. Yamauchi, and K. Kumakura, "High-power characteristics of
GaN/InGaN double heterojunction bipolar transistors," Appl. Phys. Lett. 84 (11),1964-1966 (2004).

19.

H. Matsui, T. Sato, T. Takahashi, S. C. Wang, H. B. Yang, H. Ding, T. Fujii, T.
Watanabe, and A. Matsuda, "Spectral evidence for Bogoliubov quasiparticle intriple-layered high-T-c superconductor Bi2Sr2Ca2Cu3O10," Physica C 408-10,
814-815 (2004).

20.

T. Matsuoka, H. Okamoto, H. Takahata, T. Mitate, S. Mizuno, Y. Uchiyama, and T.
Makimoto, "MOVPE growth and photoluminescence of wurtzite InN," J. Cryst.
Growth 269 (1), 139-144 (2004).

21.

M. Naito and K. Ueda, "MgB2 thin films for superconducting electronics," Supercond.
Sci. Technol. 17 (7), R1-R18 (2004).

22.

T. Nishida, T. Makimoto, H. Saito, and T. Ban, "AlGaN-based ultraviolet
light-emitting diodes grown on bulk AlN substrates," Appl. Phys. Lett. 84 (6),1002-1003 (2004).

23.

K. Onomitsu, T. Okabe, T. Makimoto, H. Saito, M. Ramsteiner, H. J. Zhu, A.
Kawaharazuka, K. Ploog, and Y. Horikoshi, "Magnetic and electric field effects ofphotoluminescence of excitons bound to nitrogen atom pairs in GaAs," Jpn. J. Appl.
Phys. Part 2 - Lett. Express Lett. 43 (6B), L756-L758 (2004).

24.

H. Sato and K. Cho, "Third-order intermodulation measurements for superconducting
bandpass filters," IEICE Trans. Electron. E87C (5), 708-713 (2004).

25.

H. Sato, J. Kurian, and M. Naito, "Third-order intermodulation measurements of- 71 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

microstrip bandpass filters based on high-temperature superconductors," IEEE Trans.
Microw. Theory Tech. 52 (12), 2658-2663 (2004).
26.

H. Sato, A. Tsukada, and M. Naito, "La-214 thin films under epitaxial strain," Physica
C 408-10, 848-852 (2004).

27.

T. Sato, H. Matsui, T. Takahashi, H. Ding, H. B. Yang, S. C. Wang, T. Fujii, T.
Watanabe, A. Matsuda, T. Terashima, and K. Kadowaki, "Fermi surface,superconducting gap, and many-body effects in Bi2Sr2Can-1CunO2n+4 (n=1-3),"
Physica C 408-10, 812-813 (2004).

28.

T. Sato, H. Matsui, K. Terashima, T. Takahashi, H. Ding, H. B. Yang, S. C. Wang, T.
Fujii, T. Watanabe, A. Matsuda, T. Terashima, and K. Kadowaki, "Magnetic
interaction in hole-doped high-T-c superconductors observed by angle-resolved
photoemission spectroscopy," Physica C 412-14, 51-58 (2004).

29.

Y. Taniyasu, M. Kasu, and T. Makimoto, "Electrical conduction properties of n-type
Si-doped AlN with high electron mobility (> 100 cm(2) V-1 s(-1))," Appl. Phys. Lett.
85 (20), 4672-4674 (2004).

30.

Y. Taniyasu, M. Kasu, and T. Makimoto, "Field emission properties of heavily
Si-doped AlN in triode-type display structure," Appl. Phys. Lett. 84 (12), 2115-2117(2004).

31.

K. Tsubaki, N. Maeda, T. Saitoh, and N. Kobayashi, "Hall resistance hysteresis in
AlGaN/GaN 2DEG," Physica E 21 (2-4), 676-678 (2004).

32.

K. Ueda and M. Naito, "Tunnel junctions on as-grown MgB2 films," Physica C
408-10, 134-135 (2004).

33.

C. X. Wang, N. Maeda, K. Tsubaki, N. Kobayashi, and T. Makimoto, "Electrontransport properties in lightly Si-doped InGaN films grown by metalorganic vapor
phase epitaxy," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (6A),
3356-3359 (2004).

34.

C. X. Wang, K. Tsubaki, N. Kobayashi, T. Makimoto, and N. Maeda, "Electrontransport properties in AlGaN/InGaN/GaN double heterostructures grown bymetalorganic vapor phase epitaxy," Appl. Phys. Lett. 84 (13), 2313-2315 (2004).

35.

H. Yamamoto, K. Aoki, A. Tsukada, and M. Naito, "Growth of Ba1-xKxBiO3 thinfilms by molecular beam epitaxy," Physica C 412-14, 192-195 (2004).

36.

H. Yamamoto, M. Naito, A. Tsukada, and S. Suzuki, "In situ angle-resolved
photoemission study of MBE-grown (La,Ce)(2)CuO4 thin films," Physica C 412-14,
134-138 (2004).

Low-Dimensional Nanomaterials Research Group1.

K. Akiba, N. Yamamoto, V. Grillo, A. Genseki, and Y. Watanabe, "Anomalous
temperature and excitation power dependence of cathodoluminescence from InAs
quantum dots," Phys. Rev. B 70 (16), 165322 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

2.

S. Bhunia, T. Kawamura, S. Fujikawa, H. Nakashima, K. Furukawa, K. Torimitsu,
and Y. Watanabe, "Vapor-liquid-solid growth of vertically aligned InP nanowires bymetalorganic vapor phase epitaxy," Thin Solid Films 464-65, 244-247 (2004).

3.

S. Bhunia, T. Kawamura, S. Fujikawa, K. Tokushima, and Y. Watanabe,"Free-standing and vertically aligned InP nanowires grown by metalorganic vapor
phase epitaxy," Physica E 21 (2-4), 583-587 (2004).

4.

S. Bhunia, T. Kawamura, S. Fujikawa, and Y. Watanabe, "Systematic investigation of
growth of InP nanowires by metalorganic vapor-phase epitaxy," Physica E 24 (1-2),
138-142 (2004).

5.

H. Hibino, Y. Homma, C. W. Hu, M. Uwaha, T. Ogino, and I. S. T. Tsong,"Structural and morphological changes on surfaces with multiple phases studied by
low-energy electron microscopy," Appl. Surf. Sci. 237 (1-4), 51-57 (2004).

6.

Y. Homma, S. Suzuki, Y. Kobayashi, M. Nagase, and D. Takagi, "Mechanism ofbright selective imaging of single-walled carbon nanotubes on insulators by scanningelectron microscopy," Appl. Phys. Lett. 84 (10), 1750-1752 (2004).

7.

Y. J. Jung, Y. Homma, R. Vajtai, Y. Kobayashi, T. Ogino, and P. M. Ajayan,"Straightening suspended single walled carbon nanotubes by ion irradiation," Nano
Lett. 4 (6), 1109-1113 (2004).

8.

Y. Kobayashi, H. Nakashima, D. Takagi, and Y. Homma, "CVD growth of
single-walled carbon nanotubes using size-controlled nanoparticle catalyst," Thin
Solid Films 464-65, 286-289 (2004).

9.

Y. Kobayashi, D. Takagi, Y. Ueno, and Y. Homma, "Characterization of carbon
nanotubes suspended between nanostructures using micro-Raman spectroscopy,"
Physica E 24 (1-2), 26-31 (2004).

10.

Y. Kobayashi, T. Yamashita, Y. Ueno, O. Niwa, Y. Homma, and T. Ogino,"Extremely intense Raman signals from single-walled carbon nanotubes suspended
between Si nanopillars," Chem. Phys. Lett. 386 (1-3), 153-157 (2004).

11.

J. Lefebvre, P. Finnie, and Y. Homma, "Temperature-dependent photoluminescencefrom single-walled carbon nanotubes," Phys. Rev. B 70 (4), 045419 (2004).

12.

J. Lefebvre, J. M. Fraser, P. Finnie, and Y. Homma, "Photoluminescence from anindividual single-walled carbon nanotube," Phys. Rev. B 69 (7), 075403 (2004).

13.

J. Lefebvre, J. M. Fraser, Y. Homma, and P. Finnie, "Photoluminescence fromsingle-walled carbon nanotubes: a comparison between suspended andmicelle-encapsulated nanotubes," Appl. Phys. A-Mater. Sci. Process. 78 (8),1107-1110 (2004).

14.

F. Lin, K. Sumitomo, Y. Homma, and T. Ogino, "STM observations of
three-dimensional Ge islands on Si(111) surfaces with different step orientations andstep-bunching conditions," Surf. Sci. 562 (1-3), 15-21 (2004).

15.

F. Maeda, E. Laffosse, Y. Watanabe, S. Suzuki, Y. Homma, M. Suzuki, T. Kitada, T.
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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

Ogiwara, A. Tanaka, M. Kimura, V. A. Mihai, H. Yoshikawa, and S. Fukushima,"Surface and interface reactions of catalysts for carbon nanotube growth on Si
substrates studied by soft X-ray photoelectron spectroscopy," Physica E 24 (1-2),
19-25 (2004).
16.

F. Maeda and Y. Watanabe, "Real-time analysis of a surface phase transition of
GaAs(001) by core-level photoelectron spectroscopy and photoelectron diffraction," J.
Electron Spectrosc. Relat. Phenom. 137-40, 107-112 (2004).

17.

F. Maeda and Y. Watanabe, "Time-resolved core-level photoelectron spectroscopy
and reflection high-energy electron diffraction study of surface phase transition on
GaAs(001)," Appl. Surf. Sci. 237 (1-4), 224-229 (2004).

18.

T. Ogino, Y. Homma, K. Ishibashi, and H. Yamaguchi, "Proceedings of theInternational symposium on Functional Semiconductors Nanostructures 2003
FSNS2003 - Held in Atsugi, Kanagawa, Japan, 12-14 November 2003 - Preface,"
Physica E 24 (1-2), VII-VII (2004).

19.

H. Omi and Y. Homma, "Stiffness of step bunches on Si(111)," Jpn. J. Appl. Phys.
Part 2 - Lett. Express Lett. 43 (6B), L822-L824 (2004).

20.

H. Omi, Y. Homma, T. Ogino, S. Stoyanov, and V. Tonchev, "Design of atomic step
networks on Si(111) through strain distribution control," J. Appl. Phys. 95 (1),263-266 (2004).

21.

K. Prabhakaran, F. Meneau, T. Murashita, G. N. Greaves, G. Sankar, Y. Homma, and
T. Gino, "Reply to "comment on luminescent nanoring structures on silicon"," Adv.
Mater. 16 (17), 1495-1496 (2004).

22.

K. Sumitomo, F. Lin, Y. Homma, and T. Ogino, "Selective formation of Ge
nanostructures on Si(111) surface with patterned steps," Appl. Surf. Sci. 237 (1-4),
68-74 (2004).

23.

S. Suzuki, K. Kanzaki, Y. Homma, and S. Y. Fukuba, "Low-acceleration-voltage
electron irradiation damage in single-walled carbon nanotubes," Jpn. J. Appl. Phys.
Part 2 - Lett. Express Lett. 43 (8B), L1118-L1120 (2004).

24.

S. Suzuki, Y. Watanabe, Y. Homma, S. Fukuba, S. Heun, and A. Locatelli, "Workfunctions of individual single-walled carbon nanotubes," Appl. Phys. Lett. 85 (1),127-129 (2004).

25.

S. Suzuki, Y. Watanabe, T. Ogino, Y. Homma, D. Takagi, S. Heun, L. Gregoratti, A.
Barinov, and M. Kiskinova, "Observation of single-walled carbon nanotubes byphotoemission microscopy," Carbon 42 (3), 559-563 (2004).

26.

D. Takagi, Y. Homma, and Y. Kobayashi, "Selective growth of individual
single-walled carbon nanotubes suspended between pillar structures," Physica E 24(1-2), 1-5 (2004).

27.

F. Toujou, S. Yoshikawa, Y. Homma, A. Takano, H. Takenaka, M. Tomita, Z. Li, T.
Hasegawa, K. Sasakawa, M. Schuhmacher, A. Merkulov, H. K. Kim, D. W. Moon, T.
Hong, and J. Y. Won, "Evaluation of BN-delta-doped multilayer reference materials- 74 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

for shallow depth profiling in SIMS: round-robin test," Appl. Surf. Sci. 231-2,
649-652 (2004).
28.

Y. Watanabe, S. Bhunia, S. Fujikawa, T. Kawamura, H. Nakashima, K. Furukawa,
and K. Torimitsu, "Heteroepitaxial metalorganic vapor phase epitaxial growth of InP
nanowires on GaP(111)B," Thin Solid Films 464-65, 248-250 (2004).

29.

Y. Watanabe, H. Hibino, S. Bhunia, K. Tateno, and T. Sekiguchi, "Site-controlled InP
nanowires grown on patterned Si substrates," Physica E 24 (1-2), 133-137 (2004).

30.

Y. Watanabe, N. Yamamoto, S. Bhunia, T. Kawamura, and S. Fujikawa, "Structuraland optical properties of vertically aligned TnP nanowires grown by metal organic
vapor phase epitaxy," Physica E 23 (3-4), 305-308 (2004).

31.

Z. H. Zhang, K. Sumitomo, F. Lin, H. Omi, and T. Ogino, "Structure transition of
Ge/Si(113) surfaces during Ge epitaxial growth," Physica E 24 (1-2), 157-160 (2004).

32.

Z. H. Zhang, K. Sumitomo, H. Omi, T. Ogino, and X. Zhu, "Ge molecular beam
epitaxy on Si(113): surface structures, nanowires and nanodots," Surf. Interface Anal.
36 (2), 114-118 (2004).

Molecular and Bio Science Research Group1.

K. Ajito, C. X. Han, and K. Torimitsu, "Detection of glutamate in optically trapped
single nerve terminals by Raman spectroscopy," Anal. Chem. 76 (9), 2506-2510(2004).

2.

K. Furukawa, H. Nakashima, K. Ajito, Y. Kashimura, W. Hu, and K. Torimitsu,"Observation and manipulation of nanestructures formed by rigid rodlike polymers,"
Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (7B), 4521-4524(2004).

3.

W. P. Hu, M. Matsumura, K. Furukawa, and K. Torimitsu, "Oxygen plasma generated
copper/copper oxides nanoparticles," J. Phys. Chem. B 108 (35), 13116-13118(2004).

4.

W. P. Hu, H. Nakashima, K. Furukawa, Y. Kashimura, K. Ajito, C. Han, and K.
Torimitsu, "Carrier injection from gold electrodes into thioacetyl-end-functionalizedpoly(para-phenyleneethynylene)s," Phys. Rev. B 69 (16), 165207 (2004).

5.

W. P. Hu, H. Nakashima, K. Furukawa, Y. Kashimura, K. Ajito, and K. Torimitsu,"Self-assembled rigid conjugated polymer nanojunction and its nonlinear
current-voltage characteristics at room temperature," Appl. Phys. Lett. 85 (1),115-117 (2004).

6.

T. Ishimoto, H. Tokiwa, H. Teramae, and U. Nagashima, "Development of an abinitio MO-MD program based on fragment MO method - an attempt to analyze thefluctuation of protein," Chem. Phys. Lett. 387 (4-6), 460-465 (2004).

7.

M. Kobayashi, J. Buck, and L. R. Levin, "Conservation of functional domain structure
in bicarbonate-regulated "soluble" adenylyl cyclases in bacteria and eukaryotes," Dev.
Genes Evol. 214 (10), 503-509 (2004).
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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

8.

K. Ohtawara and H. Teramae, "Study on optimization of molecular structure using
Hamiltonian algorithm," Chem. Phys. Lett. 390 (1-3), 84-88 (2004).

9.

I. Suzuki, Y. Sugio, H. Moriguchi, K. Takahashi, T. Kaneko, Y. Jimbo, and K.
Yasuda, "Pattern modification of a neuronal network for on-chip single-cell-based
electrophysiological measurement using photo-thermal etching of an agarosearchitecture with a multi-electrode array," Biophys. J. 86 (1), 271A-271A (2004).

10.

T. Yamazaki, Y. Murata, K. Komatsu, K. Furukawa, M. Morita, N. Maruyama, T.
Yamao, and S. Fujita, "Synthesis and electrolytic polymerization of theethylenedioxy-substituted terthiophene-fullerene dyad," Org. Lett. 6 (26), 4865-4868(2004).

Physical Science Laboratory
Nanodevices Research Group1.

T. Akiyama, H. Kageshima, and T. Ito, "First-principles analyses of O-2 moleculesaround ultrathin SiO2/Si(100) interface," Jpn. J. Appl. Phys. Part 1 - Regul. Pap.
Short Notes Rev. Pap. 43 (11B), 7903-7908 (2004).

2.

K. Degawa, T. Aoki, T. Higuchi, H. Inokawa, and Y. Takahashi, "A
single-electron-transistor logic gate family for binary, multiple-valued andmixed-mode logic," IEICE Trans. Electron. E87C (11), 1827-1836 (2004).

3.

A. Fujiwara, N. M. Zimmerman, Y. Ono, and Y. Takahashi, "Current quantization
due to single-electron transfer in Si-wire charge-coupled devices," Appl. Phys. Lett.
84 (8), 1323-1325 (2004).

4.

S. Fukatsu, K. M. Itoh, M. Uematsu, H. Kageshima, Y. Takahashi, and K. Shiraish,"Effect of Si/SiO2 interface on silicon and boron diffusion in thermally grown SiO2,"
Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (11B), 7837-7842(2004).

5.

S. Horiguchi, A. Fujiwara, H. Inokawa, and Y. Takahashi, "Analysis of back-gate
voltage dependence of threshold voltage of thin silicon-on-insulator
metal-oxide-semiconductor field-effect transistor and its application to Si
single-electron transistor," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev.
Pap. 43 (4B), 2036-2040 (2004).

6.

H. Inokawa and Y. Takahashi, "Simultaneous-sweep method for evaluation of
single-electron transistors with barriers induced by gate electric field," Jpn. J. Appl.
Phys. Part 2 - Lett. Express Lett. 43 (8B), L1048-L1050 (2004).

7.

H. Inokawa, Y. Takahashi, K. Degawa, T. Aoki, and T. Higuchi, "A simulation
methodology for single-electron multiple-valued logics and its application to a latchedparallel counter," IEICE Trans. Electron. E87C (11), 1818-1826 (2004).

8.

H. Kageshima, M. Uematsu, K. Akagi, S. Tsuneyuki, T. Akiyama, and K. Shiraishi,"Theoretical study of excess Si emitted from Si-oxide/Si interfaces," Jpn. J. Appl.
Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (12), 8223-8226 (2004).
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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

9.

S. J. Kim, Y. Ono, Y. Takahashi, and J. B. Choi, "Real-time observation of
single-electron movement through silicon single-electron transistor," Jpn. J. Appl.
Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (10), 6863-6867 (2004).

10.

S. M. Koo, A. Fujiwara, J. P. Han, E. M. Vogel, C. A. Richter, and J. E. Bonevich,"High inversion current in silicon nanowire field effect transistors," Nano Lett. 4 (11),2197-2201 (2004).

11.

K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi, "Automatic
control of oscillation phase of a single-electron transistor," IEEE Electron Device Lett.
25 (1), 31-33 (2004).

12.

K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi, "Multifunctional
Boolean logic using single-electron transistors," IEICE Trans. Electron. E87C (11),1809-1817 (2004).

13.

K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi, "Multilevel
memory using an electrically formed single-electron box," Appl. Phys. Lett. 85 (7),1277-1279 (2004).

14.

K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi, "Multilevel
memory using single-electron turnstile," Electron. Lett. 40 (4), 229-230 (2004).

15.

M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, and K. Shiraishi,"Correlated diffusion of silicon and boron in thermally grown SiO2," Appl. Phys. Lett.
85 (2), 221-223 (2004).

16.

M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, and K. Shiraishi,"Simulation of correlated diffusion of Si and B in thermally grown SiO2," J. Appl.
Phys. 96 (10), 5513-5519 (2004).

17.

M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, K. Shiraishi, and
U. Gosele, "Modeling of Si self-diffusion in SiO2: Effect of the Si/SiO2 interface
including time-dependent diffusivity," Appl. Phys. Lett. 84 (6), 876-878 (2004).

18.

N. M. Zimmerman, E. Hourdakis, Y. Ono, A. Fujiwara, and Y. Takahashi, "Error
mechanisms and rates in tunable-barrier single-electron turnstiles and charge-coupleddevices," J. Appl. Phys. 96 (9), 5254-5266 (2004).

Nanostructure Technology Research Group1.

L. F. Houlet, H. Yamaguchi, S. Miyashita, and Y. Hirayama, "InAs/AlGaSb
piezoresistive cantilever for sub-angstrom scale displacement detection," Jpn. J. Appl.
Phys. Part 2 - Lett. 43 (3B), L424-L426 (2004).

2.

R. Koch, A. K. Das, H. Yamaguchi, C. Pampuch, and A. Ney, "Perpendicularmagnetic fields in cantilever beam magnetometry," J. Appl. Phys. 96 (5), 2773-2778(2004).

3.

R. Koch, C. Pampuch, H. Yamaguchi, A. K. Das, A. Ney, L. Daweritz, and K. H.
Ploog, "Magnetoelastic coupling of MnAs/GaAs(001) close to the phase transition,"
Phys. Rev. B 70 (9), 092406 (2004).
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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

4.

M. Nagase and H. Namatsu, "A method for assembling nano-electromechanicaldevices on microcantilevers using focused ion beam technology," Jpn. J. Appl. Phys.
Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (7B), 4624-4628 (2004).

5.

K. Nakamatsu, K. Watanabe, K. Tone, T. Katase, W. Hattori, Y. Ochiai, T. Matsuo,
M. Sasago, H. Namatsu, M. Komuro, and S. Matsui, "Bilayer resist method forroom-temperature nanoimprint lithography," Jpn. J. Appl. Phys. Part 1 - Regul. Pap.
Short Notes Rev. Pap. 43 (6B), 4050-4053 (2004).

6.

H. Namatsu, "The impact of supercritical fluoro-compounds on lithography use," Jpn.
J. Appl. Phys. Part 2 - Lett. Express Lett. 43 (4A), L456-L459 (2004).

7.

M. S. M. Saifullah, D. J. Kang, K. R. V. Subramanian, M. E. Welland, K. Yamazaki,
and K. Kurihara, "Electron beam nanolithography of beta-ketoester modified
aluminum tri-sec-butoxide," J. Sol-Gel Sci. Technol. 29 (1), 5-10 (2004).

8.

H. Yamaguchi, K. Kanisawa, S. Miyashita, and Y. Hirayama, "InAs/GaAs (111)A
heteroepitaxial systems," Physica E 23 (3-4), 285-292 (2004).

9.

H. Yamaguchi, S. Miyashita, and Y. Hirayama, "Mechanical and piezoresistive
properties of InAs/AlGaSb cantilevers," Appl. Surf. Sci. 237 (1-4), 649-653 (2004).

10.

H. Yamaguchi, S. Miyashita, and Y. Hirayama, "Piezoresistive cantilevers using
InAs-based 2D heterostructures," Physica E 24 (1-2), 70-73 (2004).

11.

H. Yamaguchi, S. Miyashita, and Y. Hirayama, "Quantum-mechanical displacement
sensing using InAs/AlGaSb micromechanical cantilevers," Physica E 21 (2-4),
1053-1056 (2004).

12.

H. Yamaguchi, Y. Tokura, S. Miyashia, and Y. Hirayama, "Quantum interference
effects in the magnetopiezoresistance of InAs/AlGaSb quasi-one-dimensional electron
systems," Phys. Rev. Lett. 93 (3), 036603 (2004).

13.

T. Yamaguchi and H. Namatsu, "Effect of developer molecular size on roughness of
dissolution front in electron-beam resist," J. Vac. Sci. Technol. B 22 (3), 1037-1043(2004).

14.

T. Yamaguchi and H. Namatsu, "Impact of developers on roughness of dissolution
front in electron-beam resists," J. Photopolym. Sci. Technol. 17 (4), 557-565 (2004).

15.

T. Yamaguchi, K. Yamazaki, and H. Namatsu, "Influence of molecular weight ofresist polymers on surface roughness and line-edge roughness," J. Vac. Sci. Technol.
B 22 (6), 2604-2610 (2004).

16.

K. Yamazaki and H. Namatsu, "5-nm-order electron-beam lithography for nanodevice
fabrication," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (6B),
3767-3771 (2004).

17.

K. Yamazaki and H. Namatsu, "Two-axis-of-rotation drive system in electron-beamlithography apparatus for nanotechnology applications," Microelectron. Eng. 73-74,
85-89 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

18.

K. Yamazaki, T. Yamaguchi, and H. Namatsu, "Three-dimensional nanofabrication
with 10-nm resolution," Jpn. J. Appl. Phys. Part 2 - Lett. Express Lett. 43 (8B),
L1111-L1113 (2004).

Quantum Solid State Physics Research Group
1.

D. G. Austing, S. Tarucha, K. Muraki, F. Ancilotto, M. Barranco, A. Emperador, R.
Mayol, and M. Pi, "Integer filling factor phases in vertical diatomic artificial
molecules," Physica E 22 (1-3), 502-505 (2004).

2.

T. Fujisawa, T. Hayashi, H. D. Cheong, Y. H. Jeong, and Y. Hirayama, "Rotation andphase-shift operations for a charge qubit in a double quantum dot," Physica E 21 (2-4),
1046-1052 (2004).

3.

T. Fujisawa, T. Hayashi, and Y. Hirayama, "Controlled decoherence of a charge qubit
in a double quantum dot," J. Vac. Sci. Technol. B 22 (4), 2035-2038 (2004).

4.

T. Fujisawa, T. Hayashi, Y. Hirayama, H. D. Cheong, and Y. H. Jeong, "Electron
counting of single-electron tunneling current," Appl. Phys. Lett. 84 (13), 2343-2345(2004).

5.

N. Goel, S. J. Chung, M. B. Santos, K. Suzuki, S. Miyashita, and Y. Hirayama,"Ballistic transport in InSb quantum wells at high temperature," Physica E 20 (3-4),
251-254 (2004).

6.

N. Goel, S. J. Chung, M. B. Santos, K. Suzuki, S. Miyashita, and Y. Hirayama,"Effect of temperature on ballistic transport in InSb quantum wells," Physica E 21(2-4), 761-764 (2004).

7.

K. Hashimoto, T. Saku, and Y. Hirayama, "Nuclear-spin-related resistanceenhancements observed over a wide range of magnetic fields," Phys. Rev. B 69 (15),153306 (2004).

8.

T. Hatano, M. Stopa, W. Izumida, T. Yamaguchi, T. Ota, and S. Tarucha,"Gate-voltage dependence of inter dot coupling and Aharanov-Bohm oscillation inlaterally coupled vertical double dot," Physica E 22 (1-3), 534-537 (2004).

9.

T. Hayashi, T. Fujisawa, H. D. Cheong, Y. H. Jeong, and Y. Hirayama, "Coherent
charge oscillation in a semiconductor double quantum dot," IEEE Trans. Nanotechnol.
3 (2), 300-303 (2004).

10.

T. Ito, K. Tsutsumida, K. Nakamura, Y. Kangawa, K. Shiraishi, A. Taguchi, and H.
Kageshima, "Systematic theoretical investigations of adsorption behavior on theGaAs(001)-c(4 x 4) surfaces," Appl. Surf. Sci. 237 (1-4), 194-199 (2004).

11.

S. W. Jung, T. Fujisawa, Y. Hirayama, and Y. H. Jeong, "Background charge
fluctuation in a GaAs quantum dot device," Appl. Phys. Lett. 85 (5), 768-770 (2004).

12.

T. Kodera, W. G. van der Wiel, K. Ona, S. Sasaki, T. Fujisawa, and S. Tarucha,"High-frequency manipulation of few-electron double quantum dots - toward spin
qubits," Physica E 22 (1-3), 518-521 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

13.

N. Kumada, K. Tagashira, K. Iwata, A. Sawada, Z. F. Ezawa, K. Muraki, T. Saku, and
Y. Hirayama, "Effects of in-plane magnetic fields on spin transitions in bilayer
quantum Hall states," Physica E 22 (1-3), 36-39 (2004).

14.

N. Kumada, D. Terasawa, M. Morino, K. Tagashira, A. Sawada, Z. F. Ezawa, K.
Muraki, Y. Hirayama, and T. Saku, "Phase diagrams of v=2 and v=(2)/(3) quantum
Hall states in bilayer systems," Phys. Rev. B 69 (15), 155319 (2004).

15.

J. Lagoute, K. Kanisawa, and S. Folsch, "Manipulation and adsorption-site mappingof single pentacene molecules on Cu(111)," Phys. Rev. B 70 (24), 245415 (2004).

16.

K. Muraki, J. G. S. Lok, S. Kraus, W. Dietsche, K. von Klitzing, D. Schuh, M.
Bichler, and W. Wegscheider, "Coulomb drag as a probe of the nature ofcompressible states in a magnetic field," Phys. Rev. Lett. 92 (24), 246801 (2004).

17.

K. Ono and S. Tarucha, "Nuclear-spin-induced oscillatory current in spin-blockaded
quantum dots," Phys. Rev. Lett. 92 (25), 256803 (2004).

18.

K. Ono, K. Uchida, N. Miura, Y. Hirayama, K. Ohdaira, and Y. Shiraki, "Exciton
recombination process in GaAs/AlAs type-II heterostructures in pulsed high magnetic
fields and a uniaxial pressure," Physica E 21 (2-4), 698-702 (2004).

19.

K. Onomitsu, H. Fukui, T. Maeda, Y. Hirayama, and Y. Horikoshi, "Mn and Be
codoped GaAs for high hole concentration by low-temperature migration-enhanced
epitaxy," J. Vac. Sci. Technol. B 22 (4), 1746-1749 (2004).

20.

T. Ota, T. Hatano, K. Ono, S. Tarucha, H. Z. Song, Y. Nakata, T. Miyazawa, T.
Ohshima, and N. Yokoyama, "Single electron spectroscopy in a single pair of weakly
coupled self-assembled InAs quantum dots," Physica E 22 (1-3), 510-513 (2004).

21.

T. Ota, K. Ono, M. Stopa, T. Hatano, S. Tarucha, H. Z. Song, Y. Nakata, T.
Miyazawa, T. Ohshima, and N. Yokoyama, "Single-dot spectroscopy via elastic
single-electron tunneling through a pair of coupled quantum dots," Phys. Rev. Lett. 93(6), 066801 (2004).

22.

M. Rontani, S. Amaha, K. Muraki, F. Manghi, E. Molinari, S. Tarucha, and D. G.
Austing, "Molecular phases in coupled quantum dots," Phys. Rev. B 69 (8), 085327(2004).

23.

S. Sasaki, S. Amaha, N. Asakawa, M. Eto, and S. Tarucha, "Enhanced Kondo effectvia tuned orbital degeneracy in a spin 1/2 artificial atom," Phys. Rev. Lett. 93 (1),017205 (2004).

24.

K. Suzuki, S. Miyashita, K. Takashina, and Y. Hirayama, "Quantum Hall effect inback-gated InAs/GaSb heterostructures under a tilted magnetic field," Physica E 20(3-4), 232-235 (2004).

25.

K. Suzuki, K. Takashina, S. Miyashita, and Y. Hirayama, "Landau-level hybridizationand the quantum Hall effect in InAs/(AlSb)/GaSb electron-hole systems," Phys. Rev.
Lett. 93 (1), 016803 (2004).

26.

A. Taguchi, "Importance of the sp(2)-like orbital formation for stabilizing surface- 80 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

local structures," Physica E 24 (1-2), 153-156 (2004).
27.

A. Taguchi and K. Shiraishi, "First-principles investigations of GaAs(311)A surface
reconstruction - failure of the electron counting model," Appl. Surf. Sci. 237 (1-4),
189-193 (2004).

28.

K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, and Y. Hirayama, "Valley
splitting control in SiO2/Si/SiO2 quantum wells in the quantum Hall regime," Phys.
Rev. B 69 (16), 161304 (2004).

29.

K. Takashina, A. Fujiwara, Y. Takahashi, and Y. Hirayama, "Resistance spikes
induced by gate-controlled valley-splitting in silicon," Int. J. Mod. Phys. B 18 (27-29),
3603-3608 (2004).

30.

K. Takashina, Y. Hirayama, A. Fujiwara, S. Horiguchi, and Y. Takahashi, "A siliconbi-layer system," Physica E 22 (1-3), 72-75 (2004).

31.

D. Terasawa, M. Morino, K. Nakada, S. Kozumi, A. Sawada, Z. F. Ezawa, N.
Kumada, K. Muraki, T. Saku, and Y. Hirayama, "Simultaneous excitation of spins
and pseudospins in the bilayer v=1 quantum Hall state," Physica E 22 (1-3), 52-55(2004).

32.

D. Terasawa, K. Nakada, S. Kozumi, Z. F. Ezawa, A. Fukuda, A. Sawada, N. Kumada,K. Muraki, Y. Hirayama, and T. Saku, "Double magnetoresistance minima induced by
the in-plane magnetic field for the v=1 double-layer quantum Hall state," Int. J. Mod.
Phys. B 18 (27-29), 3709-3712 (2004).

33.

H. Yokoyama, T. Sato, K. Ono, Y. Hirayama, and S. Tarucha, "Tunable quantum dot
resonator embedded in a quantum wire," Physica E 21 (2-4), 527-531 (2004).

34.

G. Yusa, K. Hashimoto, K. Muraki, T. Saku, and Y. Hirayama, "Self-sustaining
resistance oscillations: Electron-nuclear spin coupling in mesoscopic quantum Halldevices," Phys. Rev. B 69 (16), 161302 (2004).

35.

G. Yusa, K. Muraki, T. Saku, and Y. Hirayama, "Intralayer backscattering in narrow
GaAs/AlxGa1-xAs/GaAs bilayer channels," Phys. Rev. B 69 (8), 085323 (2004).

Superconducting Quantum Physics Research Group1.

P. Bertet, I. Chiorescu, K. Semba, C. J. P. M. Harmans, and J. E. Mooij, "Detection ofa persistent-current qubit by resonant activation," Phys. Rev. B 70 (10), 100501(2004).

2.

I. Chiorescu, P. Bertet, K. Semba, Y. Nakamura, C.J.P.M. Harmans, and J. E. Mooij,"Coherent dynamics of a flux qubit coupled to a harmonic oscillator," Nature 431(7005), 159-162 (2004).

3.

F. Deppe, S. Saito, H. Tanaka, and H. Takayanagi, "Determination of the capacitanceof nm scale Josephson junctions," J. Appl. Phys. 95 (5), 2607-2613 (2004).

4.

T. Mukai and M. Yamashita, "Efficient rapid production of a Bose-Einsteincondensate by overcoming serious three-body loss," Phys. Rev. A 70 (1), 013615- 81 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)(2004).
5.

S. Saito, M. Thorwart, H. Tanaka, M. Ueda, H. Nakano, K. Semba, and H.
Takayanagi, "Multiphoton transitions in a macroscopic quantum two-state system,"Phys. Rev. Lett. 93 (3), 037001 (2004).

6.

F. Shimizu, "Scalable quantum computer with optical lattices," Jpn. J. Appl. Phys.
Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (12), 8376-8382 (2004).

Spintronics Research Group1.

T. Akazaki, H. Yamaguchi, and H. Takayanagi, "Nonequilibrium transport of
InAs/GaAs(111)A heterostructures coupled with superconducting Nb electrodes,"Semicond. Sci. Technol. 19 (4), S182-S184 (2004).

2.

Y. Asari, K. Takeda, and H. Tamura, "Hund's first and second rules in sphericalquantum dots (I) in the zero-magnetic field," Jpn. J. Appl. Phys. Part 1 - Regul. Pap.
Short Notes Rev. Pap. 43 (7A), 4424-4433 (2004).

3.

D. G. Austing, S. Tarucha, H. Tamura, K. Muraki, F. Ancilotto, M. Barranco, A.
Emperador, R. Mayol, and M. Pi, "Integer filling factor phases and isospin in verticaldiatomic artificial molecules," Phys. Rev. B 70 (4), 045324 (2004).

4.

J. Haruyama, K. Takazawa, S. Miyadai, A. Takeda, N. Hori, I. Takesue, Y. Kanda, T.
Akazaki, and H. Takayanagi, "Supercurrent in diffusive multi-walled carbon
nanotubes," Physica C 408-10, 85-87 (2004).

5.

T. Koga, J. Nitta, and M. van Veenhuizen, "Ballistic spin interferometer using the
Rashba effect," Phys. Rev. B 70 (16), 161302 (2004).

6.

Y. Lin, J. Nitta, T. Koga, and T. Akazaki, "Electron g factor in a gated InGaAschannel with double InAs-inserted wells," Physica E 21 (2-4), 656-660 (2004).

7.

F. E. Meijer, A. F. Morpurgo, T. M. Klapwijk, T. Koga, and J. Nitta, "Competition
between spin-orbit interaction and Zeeman coupling in Rashba two-dimensional
electron gases," Phys. Rev. B 70 (20), 210307 (2004).

8.

F. E. Meijer, A. F. Morpurgo, T. M. Klapwijk, T. Koga, and J. Nitta, "Statisticalsignificance of the fine structure in the frequency spectrum of Aharonov-Bohm
conductance oscillations," Phys. Rev. B 69 (3), 035308 (2004).

9.

F. E. Meijer, J. Nitta, T. Koga, A. F. Morpurgo, and T. M. Klapwijk, "Experiments on
Aharonov-Bohm conductance oscillations: a statistical analysis of the averaged
Fourier spectrum," Physica E 22 (1-3), 402-405 (2004).

10.

J. Nitta, Y. P. Lin, T. Koga, and T. Akazaki, "Electron g-factor in a gated
InAs-inserted-channel In0.53Ga0.47As/In0.52Al0.48As heterostructure," Physica E
20 (3-4), 429-432 (2004).

11.

A. Richter, M. Yamaguchi, T. Akazaki, H. Tamura, and H. Takayanagi,"Single-electron charging effects in a semiconductor quantum wire with side-coupled
quantum dot," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (10),- 82 -

Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

7144-7149 (2004).
12.

P. V. Santos, J. Nitta, and K. H. Ploog, "Stern-Gerlach spin filter using surface
acoustic waves," Solid State Commun. 132 (9), 631-634 (2004).

13.

Y. Sekine, J. Nitta, T. Koga, A. Oiwa, S. Yanagi, T. Slupinski, and H. Munekata,"Magnetization reversal process of submicrometer-scale Hall bars of ferromagnetic
semiconductor p-In0.97Mn0.03As," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short
Notes Rev. Pap. 43 (4B), 2097-2100 (2004).

14.

M. Steiner, G. Meier, U. Merkt, and J. Nitta, "Magnetic transitions of permalloy ringsin hybrid devices," Physica E 24 (1-2), 124-128 (2004).

15.

M. Steiner and J. Nitta, "Control of magnetization states in microstructured permalloyrings," Appl. Phys. Lett. 84 (6), 939-941 (2004).

16.

K. Shiraishi, H. Tamura, and H. Takayanagi, "Theoretical design of a semiconductor
ferromagnet based on quantum dot superlattices," Physica E 24 (1-2), 107-110 (2004).

17.

I. Takesue, T. Akazaki, S. Miyadai, N. Kobayashi, A. Tokita, M. Nomura, J.
Haruyama, and H. Takayanagi, "Multi-walled carbon nanotubes with NbN
superconducting electrodes," Physica E 24 (1-2), 32-36 (2004).

18.

H. Tamura, K. Shiraishi, and H. Takayanagi, "Tunable exchange interaction inquantum dot devices," Jpn. J. Appl. Phys. Part 2 - Lett. Express Lett. 43 (5B),
L691-L693 (2004).

Optical Science Laboratory
Quantum Optical State Control Research Group1.

D. Fattal, E. Diamanti, K. Inoue, and Y. Yamamoto, "Quantum teleportation with aquantum dot single photon source," Phys. Rev. Lett. 92 (3), 037904 (2004).

2.

D. Fattal, K. Inoue, J. Vuckovic, C. Santori, G. S. Solomon, and Y. Yamamoto,"Entanglement formation and violation of Bell's inequality with a semiconductor
single photon source," Phys. Rev. Lett. 92 (3), 037903 (2004).

3.

K. M. C. Fu, T. D. Ladd, C. Santori, and Y. Yamamoto, "Optical detection of the spinstate of a single nucleus in silicon," Phys. Rev. B 69 (12), 125306 (2004).

4.

T. Hong, M. W. Jack, and M. Yamashita, "On-demand single-photon state generation
via nonlinear absorption," Phys. Rev. A 70 (1), 013814 (2004).

5.

T. Honjo, K. Inoue, and H. Takahashi, "Differential-phase-shift quantum key
distribution experiment with a planar light-wave circuit Mach-Zehnderinterferometer," Opt. Lett. 29 (23), 2797-2799 (2004).

6.

K. Inoue and K. Shimizu, "Generation of quantum-correlated photon pairs in opticalfiber: Influence of spontaneous Raman scattering," Jpn. J. Appl. Phys. Part 1 - Regul.
Pap. Short Notes Rev. Pap. 43 (12), 8048-8052 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

7.

Y. X. Liu, A. K. Ozdemir, A. Miranowicz, M. Koashi, and N. Imoto, "Exciton
entanglement in two coupled semiconductor microcrystallites," J. Phys. A-Math. Gen.
37 (15), 4423-4436 (2004).

8.

Y. X. Liu, S. K. Ozdemir, A. Miranowicz, and N. Imoto, "Kraus representation of adamped harmonic oscillator and its application," Phys. Rev. A 70 (4), 042308 (2004).

9.

F. Morikoshi, M. F. Santos, and V. Vedral, "Accessibility of physical states andnon-uniqueness of entanglement measure," J. Phys. A-Math. Gen. 37 (22), 5887-5893(2004).

10.

Y. Narumi, K. Kindo, M. Hagiwara, H. Nakano, A. Kawaguchi, K. Okunishi, and M.
Kohno, "High-field magnetization of S=1 antiferromagnetic bond-alternating chain
compounds," Phys. Rev. B 69 (17), 174405 (2004).

11.

S. K. Ozdemir, J. Shimamura, and N. Imoto, "Quantum advantage does not survive inthe presence of a corrupt source: optimal strategies in simultaneous move games,"
Phys. Lett. A 325 (2), 104-111 (2004).

12.

S. K. Ozdemir, J. Shimamura, F. Morikoshi, and N. Imoto, "Dynamics of adiscoordination game with classical and quantum correlations," Phys. Lett. A 333(3-4), 218-231 (2004).

13.

C. Santori, D. Fattal, J. Vuckovic, G. S. Solomon, E. Waks, and Y. Yamamoto,"Submicrosecond correlations in photoluminescence from InAs quantum dots," Phys.
Rev. B 69 (20), 205324 (2004).

14.

C. Santori, D. Fattal, J. Vuckovic, G. S. Solomon, and Y. Yamamoto, "Single-photon
generation with InAs quantum dots," New J. Phys. 6, 89 (2004).

15.

J. Shimamura, S. K. Ozdemir, F. Morikoshi, and N. Imoto, "Entangled states thatcannot reproduce original classical games in their quantum version," Phys. Lett. A
328 (1), 20-25 (2004).

16.

J. Shimamura, S. K. Ozdemir, F. Morikoshi, and N. Imoto, "Quantum and classicalcorrelations between players in game theory," Int. J. Quantum Inf. 2 (1), 79-89(2004).

17.

H. Takesue and T. Horiguchi, "Broad-band lightwave synthesized frequency sweeper
using synchronous filtering," J. Lightwave Technol. 22 (3), 755-762 (2004).

18.

H. Takesue and K. Inoue, "Generation of polarization-entangled photon pairs andviolation of Bell's inequality using spontaneous four-wave mixing in a fiber loop,"
Phys. Rev. A 70 (3), 031802 (2004).

19.

Y. Tokura, "Current noise in a quantum point contact," Physica E 22 (1-3), 284-287(2004).

20.

E. Waks, E. Diamanti, B. C. Sanders, S. D. Bartlett, and Y. Yamamoto, "Direct
observation of nonclassical photon statistics in parametric down-conversion," Phys.
Rev. Lett. 92 (11), 113602 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

21.

M. Yamashita, "Dynamics of evaporative cooling and growth of a Bose-Einsteincondensate," Laser Phys. 14 (4), 597-602 (2004).

Quantum Optical Physics Research Group
1.

N. I. Cade, R. Roshan, M. Hauert, A. C. Maciel, J. F. Ryan, A. Schwarz, T. Schapers,and H. Luth, "Carrier relaxation in GaAs v-groove quantum wires and the effects oflocalization," Phys. Rev. B 70 (19), 195308 (2004).

2.

R. A. Ganeev, T. Kanai, A. Ishizawa, T. Ozaki, and H. Kuroda, "Development andapplications of a compact hybrid tabletop terawatt chirped-pulse amplification Ti:
sapphire-Nd: glass laser for x-ray lasing and harmonic generation," Appl. Optics 43(6), 1396-1403 (2004).

3.

H. Gotoh, H. Kamada, T. Saitoh, H. Ando, and J. Temmyo, "Effects of biexcitons on
exciton decoherence processes in InxGa1-xAs quantum dots," Phys. Rev. B 69 (15),155328 (2004).

4.

H. Gotoh, H. Kamada, T. Saitoh, H. Ando, and J. Temmyo, "Effects of
exciton-biexciton coherent coupling on exciton absorption in quantum dots," Appl.
Phys. Lett. 85 (16), 3480-3482 (2004).

5.

H. Gotoh, H. Kamada, T. Saitoh, S. Shigemori, and J. Temmyo, "Positional control ofself-assembled quantum dots by patterning nanoscale SiN islands," Appl. Phys. Lett.
85 (14), 2836-2838 (2004).

6.

H. Gotoh, S. Shigemori, H. Kamada, T. Saitoh, and J. Temmyo, "Spatially orderedself-assembled quantum dots with uniform shapes fabricated by patterning nanoscale
SiN islands," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 43 (10),6894-6899 (2004).

7.

S. Hughes, "Enhanced single-photon emission from quantum dots in photonic crystal
waveguides and nanocavities," Opt. Lett. 29 (22), 2659-2661 (2004).

8.

S. Hughes, "High-field wave packets in semiconductor quantum wells: A real-space
finite-difference time-domain formalism," Phys. Rev. B 69 (20), 205308 (2004).

9.

S. Hughes and H. Kamada, "Single-quantum-dot strong coupling in a semiconductor
photonic crystal nanocavity side coupled to a waveguide," Phys. Rev. B 70 (19),195313 (2004).

10.

H. Kamada and H. Gotoh, "Quantum computation with quantum dot excitons,"
Semicond. Sci. Technol. 19 (4), S392-S396 (2004).

11.

A. Nakamura, J. Ishihara, S. Shigemori, K. Yamamoto, T. Aoki, H. Gotoh, and J.
Temmyo, "Characterization of wurtzite Zn1-xCdxO films using remote
plasma-enhanced metalorganic chemical vapor deposition," Jpn. J. Appl. Phys. Part 2- Lett. Express Lett. 43 (11A), L1452-L1454 (2004).

12.

H. Nakano, A. A. Andreev, and J. Limpouch, "Femtosecond X-ray line emission frommultilayer targets irradiated by short laser pulses," Appl. Phys. B-Lasers Opt. 79 (4),469-476 (2004).
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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

13.

T. Nishikawa, H. Nakano, K. Oguri, N. Uesugi, K. Nishio, and H. Masuda,"Nanohole-array size dependence of soft x-ray generation enhancement fromfemtosecond-laser-produced plasma," J. Appl. Phys. 96 (12), 7537-7543 (2004).

14.

T. Nishikawa, S. Suzuki, Y. Watanabe, O. Zhou, and H. Nakano, "Efficientwater-window X-ray pulse generation from femtosecond-laser-produced plasma byusing a carbon nanotube target," Appl. Phys. B-Lasers Opt. 78 (7-8), 885-890 (2004).

15.

K. Oguri, T. Nishikawa, T. Ozaki, and H. Nakano, "Sampling measurement ofsoft-x-ray-pulse shapes by femtosecond sequential ionization of Kr+ in an intenselaser field," Opt. Lett. 29 (11), 1279-1281 (2004).

16.

K. Oguri, T. Ozaki, T. Nishikawa, and H. Nakano, "Femtosecond-resolution
measurement of soft-X-ray pulse duration using ultra-fast population increase of
singly charged ions induced by optical-field ionization," Appl. Phys. B-Lasers Opt. 78(2), 157-163 (2004).

17.

K. Tateno, H. Gotoh, and Y. Watanabe, "GaAs/AlGaAs nanowires capped with
AlGaAs layers on GaAs(311)B substrates," Appl. Phys. Lett. 85 (10), 1808-1810(2004).

18.

T. Tawara, H. Gotoh, T. Akasaka, N. Kobayashi, and T. Saitoh, "Cavity polaritons in
InGaN microcavities at room temperature," Phys. Rev. Lett. 92 (25), 256402 (2004).

19.

R. Yano, H. Gotoh, Y. Hirayama, and S. Miyashita, "Systematic pump-probeterahertz wave emission spectroscopy of a photoconductive antenna fabricated on
low-temperature grown GaAs," J. Appl. Phys. 96 (7), 3635-3638 (2004).

20.

R. Yano, H. Gotoh, Y. Hirayama, S. Miyashita, Y. Kadoya, K. Kusuda, and M.
Yamanishi, "Low-frequency spectral enhancement of THz electromagnetic waves
emitted from InAs surface with increased excitation intensity," J. Appl. Phys. 95 (4),2141-2145 (2004).

Photonic Nano-Structure Research Group
1.

G. H. Kim, Y. H. Lee, A. Shinya, and M. Notomi, "Coupling of small, low-loss
hexapole mode with photonic crystal slab waveguide mode," Opt. Express 12 (26),6624-6631 (2004).

2.

M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H. Y. Ryu, T. Kawabata, T.
Tsuchizawa, T. Watanabe, T. Shoji, and K. Yamada, "Photonic-band-gap waveguides
and resonators in SOI photonic crystal slabs," IEICE Trans. Electron. E87C (3),398-408 (2004).

3.

M. Notomi, A. Shinya, S. Mitsugi, E. Kuramochi, and H. Y. Ryu, "Waveguides,
resonators and their coupled elements in photonic crystal slabs," Opt. Express 12 (8),1551-1561 (2004).

4.

M. Notomi, H. Suzuki, T. Tamamura, and K. Edagawa, "Lasing action due to thetwo-dimensional quasiperiodicity of photonic quasicrystals with a Penrose lattice,"
Phys. Rev. Lett. 92 (12), 123906 (2004).

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Research Activities in NTT Basic Research Laboratories Vol. 15 (June, 2005)

5.

T. Okuda, H. Kiwata, T. Matsushima, T. Wakita, A. Harasawa, K. Ono, T. Kihara, M.
Oshima, A. Yokoo, and T. Kinoshita, "Magnetic domain imaging of Ni micro ringand micro dot array by photoelectron emission microscopy," Jpn. J. Appl. Phys. Part 1- Regul. Pap. Short Notes Rev. Pap. 43 (7A), 4179-4184 (2004).

6.

H. Y. Ryu, M. Notomi, G. H. Kim, and Y. H. Lee, "High quality-factor
whispering-gallery mode in the photonic crystal hexagonal disk cavity," Opt. Express
12 (8), 1708-1719 (2004).

7.

H. Y. Ryu, M. Notomi, E. Kuramoti, and T. Segawa, "Large spontaneous emission
factor (> 0.1) in the photonic crystal monopole-mode laser," Appl. Phys. Lett. 84 (7),1067-1069 (2004).

8.

H. Suzuki, A. Yokoo, and M. Notomi, "Organic emissive materials and devices forphotonic communication," Polym. Adv. Technol. 15 (1-2), 75-80 (2004).

9.

A. Yokoo, H. Suzuki, and M. Notomi, "Organic photonic crystal band edge laser
fabricated by direct nanoprinting," Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes
Rev. Pap. 43 (6B), 4009-4011 (2004).

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Editorial Committee
Hisashi Sato
Tomoaki Kawamura
Kenji Yamazaki
Tetsuya Mukai
Hideki Goto

NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi-shi
Kanagawa 243-0198 Japan
Phone: +81-46-240-3312
URL: http://www.brl.ntt.co.jp
E-mail: kensui@will.brl.ntt.co.jp