Research Activities
in
NTT Basic Research Laboratories
Volume 13
Fiscal 2002

June 2003
NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation (NTT)http://www.brl.ntt.co.jp

1.0

SourcePositive

Gate-2

Drain current (pA)

Gate-1

T = 25 K
f = 1 MHzDrain

0.5 phase shift
I = ef = 160 fA

0.0
I = -ef = -160 fA-0.5

Negativephase shift-1.0-30-20-10 0 10 20 30
Drain voltage (mV)Electron microscope image

DC characteristics

AC characteristics (pump operation)

Silicon Single-Electron Pump

Semiconductor Hall device

B
MicroMicro-magnet

RH(ohm)The single-electron pump can literally transfer single electrons even under reverse bias
conditions, with negligibly small power dissipation and extremely high transfer accuracy. We
proposed a new device structure for the pump, and fabricated the world’s first silicon-based
single-electron pump. (Page 16)
2
1
0
-1
-2
-40

-20

0
20
B (mT)

40

Hall resistance hysteresis loop

(0.24 µm x 5 µm)

Semiconductor/ferromagnet
hybrid structure-20 mT -19.2 mT -19 mT-18mT

Magnetic force microscopy (MFM)
observation for a micro-magnet

Hysteresis in micro-magnet
The hysteresis loop measurement on a micro-magnet is difficult even by using commercial
SQUID susceptometers. A semiconductor/ferromagnet hybrid structure provides a sufficiently
high sensitivity to measure the coercive field of individual micro-magnet. The magnetic force
microscopy (MFM) observation agrees with the Hall-resistance hysteresis loop.

Compound Semiconductor Micro/Nanomechanical Devices
We are developing novel micro/nanomechanical devices by integrating semiconductor
quantum structures into mechanical cantilevers. The figure shows a scanning electron
microscope image of a heterostructure displacement sensor, where an InAs/AlGaSb twodimensional electron Hall device is integrated in a mechanical cantilever. We confirmed a
drastic improvement of displacement sensitivity induced by quantum mechanical effects.
(Page 27)

Spot-Size Converters for Photonic Crystal Waveguides
Novel spot-size converters that enable efficient coupling between photonic crystal
waveguides and single-mode fibers have been realized. The coupling loss had been thought tobe one of major problems for photonic-crystal-based integrated circuit application, and thisdevice has successfully reduced the coupling loss from 30dB to 3-4dB. (Page 34)

Preface
We greatly appreciate your support andinterest in the research activities of NTT Basic
Research Laboratories.
The objectives of the NTT Basic ResearchLaboratories are to find new scientific principles
and create innovative technologies that will
form the infrastructure of an information
sharing society characterized by “Resonant
Communication“. As we move toward our goals,
we continue to pioneer research fields bydeveloping innovative technologies and to
produce outstanding scientific achievements.
Our research interests are device physics,
functional
materialscience,quantummechanical physics, and quantum optics, andthis work engages the efforts of about one
hundred researchers. Nanotechnology designed to control nano-structures at molecularand atomic levels and Quantum Information Technology based on quantum mechanicalprinciples are key words in relation to our research activities.
To maintain our innovative research activities and open the frontiers of science, we
believe it is essential to pursue an open research policy and recognize the wide varietyof talent that exists around the world. We run various scientific exchange programs with
universities and institutes and undertake many joint projects. Moreover, international
symposia are regularly held to promote further progress in specific research fields. We
hosted the International Symposium, Carrier Interactions and Spintronics in
Nanostructures in March this year.
This booklet, “Research Activities in NTT Basic Research Laboratories Vol. 13,”
provides an overview of our research activities in 2002. We hope this booklet willencourage mutual understanding and further collaboration among all scientists.
June 2003

Dr. Sunao Ishihara
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: ishihara@nttbrl.jp

Contents
page

Member List.......................................................................................................................... 1
I. Research Topics◆Overview of Device Physics Research............................................................................... 15♦ Silicon Single-Electron Pump
♦ Analysis of Ultrathin Resist Film
♦ Electronic Structure at Carbon Nanotube Tips Studied by Photoemission Microscopy♦ Anisotropic Strain for Controlled Growth of Nanostructures◆Overview of Materials Science Research........................................................................... 20♦ Plasticity in Neuronal Networks♦ Artificial Coordination Control in Copper Oxides by Molecular Beam Epitaxy– New Strategy for Material Synthesis –♦ Design of Superconductor in Quantum Dot Superlattices♦ Control of Spin-Orbit Interaction in a Semiconductor◆Overview of Quantum Electron Physics Research ............................................................ 25♦ Long-lived Spin States in a Quantum Dot♦ Compound Semiconductor Micro/Nanomechanical Devices♦ Nitride Heterojunction Bipolar Transistor with Regrown Base Layer♦ Optical Band-Gap Energy of Wurtzite InN◆Overview of Quantum Optics and Optical Materials Research ......................................... 30♦ Quantum Cryptography Experiment Using a Single-Photon Source♦ High-order Harmonic Generation from Surface Plasma♦ High Reflective Distributed Bragg Reflectors Using a Deeply-Etched
Semiconductor/Air Grating for InGaN/GaN Laser Diodes♦ Spot-Size Converter of Photonic Crystal Waveguide

II. Data◆International Symposium on Carrier Interactions and Spintronics in Nanostructures....... 35◆Workshop on Surface & Nano-Science in NTT................................................................. 36◆Science Plaza 2002............................................................................................................. 36◆Award Winner’s List .......................................................................................................... 37◆In-house Award Winner’s List ........................................................................................... 38◆List of Visitor’s Talks ......................................................................................................... 39◆Research Activities of Basic Research Laboratories in 2002 ............................................ 44◆List of Invited Talks at International Conferences ............................................................. 46

Member List
As of March 31, 2003(*/ left NTT BRL in the middle of the year)

NTT Basic Research Laboratories
Director, Dr. Sunao Ishihara

Research Planning Section

Executive Manager,

Dr. Masao Morita

Executive Manager,

Dr. Yasuyuki Kobayashi

Senior Research Scientist,

Dr. Yuichi Harada

NTT R&D Fellow
Prof. Yoshihisa Yamamoto(Stanford University, USA)
Dr. Hideaki Takayanagi(Executive Manager, Materials Science Laboratory)

NTT Research Professor
Prof. Nobuyuki Imoto(The Graduate University for Advanced Studies)Prof. Masahito Ueda
(Tokyo Institute of Technology)
Prof. Seigo Tarucha(The University of Tokyo)-1-Device Physics Laboratory

Executive Manager,

Dr. Yasuo Takahashi
Dr. Toshio Ogino*
Dr. Koji Sumitomo
Takeshi Karasawa

Silicon Nanodevices Research Group:
Dr. Yasuo Takahashi (Group Leader)Dr. Hiroshi Inokawa
Dr. Seiji Horiguchi
Dr. Yukinori Ono
Dr. Akira Fujiwara
Dr. Katsuhiko Nishiguchi
Dr. Toru Akiyama

Dr. Masashi Uematsu
Dr. Hiroyuki Kageshima

Nanostructure Technology Research Group:
Dr. Hideo Namatsu (Group Leader)
Kenji Yamazaki
Dr. Masao Nagase
Toru Yamaguchi
Dr. Kenichi Kanzaki

Junzo Hayashi
Yoshio Watanabe

Surface Science Research Group:
Dr. Yoshikazu Homma (Group Leader)
Dr. Yoshihiro Kobayashi
Dr. Yoshio Watanabe
Dr. Tomoaki Kawamura
Dr. Hiroo Omi
Dr. Satoru Suzuki
Dr. Feng Lin*Dr. Fumihiko Maeda
Dr. Prabhakaran Kuniyil
Dr. Satyaban Bhunia-2-Materials Science Laboratory

Executive Manager,

Dr. Hideaki Takayanagi
Dr. Kazuhiro Igeta

Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Michiya Fujiki*
Dr. Keisuke Ebata
Dr. Kazuaki Furukawa
Dr. Katsuhiro Ajito
Dr. Yoshiaki Kashimura
Dr. Hiroshi Nakashima
Superconducting Thin Films Research Group:
Dr. Michio Naito (Group Leader)Dr. Hideki Yamamoto
Dr. Hiroyuki Shibata
Dr. Kenji Ueda
Dr. Jose KurianSuperconducting Quantum Physics Research Group:
Dr. Hideaki Takayanagi (Group Leader)
Dr. Azusa Matsuda
Dr. Kouichi Semba
Dr. Hayato Nakano
Dr. Noriyuki Hatakenaka
Hirotaka Tanaka
Dr. Shiro Saito
Dr. Minoru Kawamura
Dr. Andreas Richter
Spintronics Research Group:
Dr. Junsaku Nitta (Group Leader)
Dr. Kotaro Tsubaki*
Dr. Yoshiaki Sekine-3-

Dr. Yasuhiko Jimbo
Dr. Nahoko Kasai
Dr. Chunxi Han

Dr. Shin-ichi Karimoto

Dr. Tatsushi Akazaki
Dr. Hiroyuki Tamura
Dr. Kenichi Matsuda*

Dr. Yiping Lin

Physical Science Laboratory

Executive Manager,

Dr. Yoshiro Hirayama
Dr. Takaaki Mukai*
Masami Kumagai

Quantum Solid State Physics Research Group:
Dr. Yoshiro Hirayama (Group Leader)Dr. Hiroshi Yamaguchi
Dr. Toshimasa Fujisawa
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki
Kyoichi Suzuki
Dr. Toshiaki Hayashi
Dr. Lionel Houlet
Dr. Kei Takashina
Wide-Bandgap Semiconductor Research Group:
Dr. Naoki Kobayashi (Group Leader)
Dr. Toshiki Makimoto
Dr. Makoto Kasu
Dr. Toshio NishidaDr. Narihiko Maeda
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Dr. Yoshitaka Taniyasu
Dr. Chengxin Wang

Dr. Koji Muraki
Dr. Akihito Taguchi
Dr. Takeshi Yusa

Dr. Takashi Matsuoka
Yoshiharu Yamauchi
Masanobu Hiroki

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kyou Inoue
Dr. Kaoru Shimizu
Dr. Tetsuya Mukai
Dr. Fumiaki Morikoshi
Dr. Itakura Toshifumi
Dr. Tao Hong

Dr. Makoto Yamashita
Dr. Bingyang Zhang*
Dr. Michael Wong Jack

Ultrafast Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Tadashi Nishikawa
Dr. Ryuzi Yano
Dr. Atsushi Ishizawa
Dr. Tsuneyuki Ozaki

Katsuya Oguri
Dr. Jingquan Lin*

-4-

Optical Device Physics Research Group:
Dr. Tadashi Saitoh (Group Leader)
Dr. Tetsuomi Sogawa
Hidehiko Kamada
Dr. Takehiko Tawara
Dr. Hailong Wang*
Photonic Nano-Structure Research Group:
Dr. Yoshiro Hirayama (Group Leader)
Dr. Nobuhiko Susa
Dr. Masaya Notomi
Dr. Atsushi Yokoo
Dr. Akihiko Shinya
Dr. Han-Youl Ryu-5-

Dr. Hideki Gotoh

Eiichi Kuramochi
Dr. Mistugi Satoshi

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 using metalorganic vapor
phase epitaxy (MOVPE) and flow-rate modulation epitaxy (FME), in-situ monitoring of
epitaxial growth using surface photo-absorption (SPA), characterization of heavily doped
semiconductors, heterojunction bipolar transistors (HBTs), and nano-structure selective area
growth using scanning tunnel microscopy (STM). His current interests are epitaxial growth of
nitride semiconductors and nitride semiconductor devices. He is a member of the Japan
Society of Applied Physics, the Institute of Electronics, Information and Communication
Engineers, and Materials Research Society.

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 molecularbeam 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) since 2001. He is an associate editor of Japanese Journal of Applied Physics,
and a member of the Japan society of Applied Physics and the Physical Society of Japan.
-6-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
1991 he has engaged in the study of semiconductor fine structures fabricated byfocused-ion-beam technique and electron-beam lithography technique, transportcharacteristics of semiconductor quantum dot. His current interests are single-electron
dynamics in quantum dots, and their application to quantum information technologies. He is amember of the Japan Society of Applied Physics, and the Physical Society of Japan.

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.

-7-Advisory Board (2002 Fiscal Year)
Name

Title
Affiliation

Dr. Johan E. Mooij

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

Dr. C. Tord Claeson

Professor
Physics Department
Chalmers University of Technology, Sweden

Dr. Klaus von Klitzing

Professor
Max-Planck-Institut für Festkörperforschung,Germany

Dr. Klaus H. Ploog

Director
Paul-Drude-Institut für Festkörperelektronik,
Germany

Dr. Michel H. Devoret

Professor
Department of Applied Physics
Yale University, USA

Dr. Christos Flytzanis

Professor
Physics of Condensed Matter Laboratory
Ecole Normale Supérieure, France

Dr. Chung L. Tang

Professor
School of Electrical Engineering
Cornell University, UＳA-8-

Invited Scientists(2002 Fiscal Year)

Name

Affiliation
PeriodDr. Hai-Du Cheong

Pohang University of Science and Technology, Korea
September 01– August 02

Dr. Takaaki Koga

Japan Science and Technology Corporation (JST), Japan
December 01 – November 04

Prof. Gerrit E. W. Bauer

Delft University of Technology, The Netherlands
March – June 02

Dr. Vladimir Seleznev

Institute of Semiconductor Physics
Siberian Branch of the Russian Academy of Sciences, Russia
March – June 02

Dr. Alexander Andreev

Institute for Laser Physics
Research Center "S.I. Vavilov State Optical Institute", Russia
April – June 02

Prof. Zhaohui Zhang

Peking University, China
July – September 02

Prof. Hai-Du Cheong

Keimyung University, Korea
January - February 03-9-Trainees(2002 Fiscal Year)

Name

Affiliation (Period)

Richard Engstrom

Chalmers University of Technology, Sweden(Sep. 01 – Aug. 02)

Frank Erik Meijer

Delft University of Technology, The Netherlands(Feb. – Aug. 02)

Kenny Shan Kivong

Institut National Des Sciences Appliquées, France(Mar. – Aug. 02)

Stephane Marcet

Institut National Des Sciences Appliquées, France(Mar. – Aug. 02)

Frank Deppe

Technische Universität München, Germany(May 02 – May 05)

Yung Joon Jung

Rensselaer Polytechnic Institute, USA(May – Nov. 02)

Jeremy Graham

University of Oklahoma, USA(Jun. – Aug. 02)

Simon Perraud

École Supérieure de Physique et de Chimie Industrielles,
France (Jul. – Dec. 02)

Guillaume Lang

École Supérieure de Physique et de Chimie Industrielles,
France (Jul. – Dec. 02)

Alexandre Soujaeff

Laboratoire GTL-CNRS-Telecom, France(Jul. - Sep. 02)

Niti Goel

University of Oklahoma, USA(Sep. – Oct. 02)

Florian Meneau

The University of Wales in Aberystwyth, UK(Sep. 02)-10-

Marc van Veenhuizen

Rijksuniversiteit Groningen
University of Groningen, The Netherlands(Sep. 02 – Feb. 03)

Oliver Regenfelder

Technische Universität Graz, Austria(Sep. 02 – Aug. 03)

Yoshiharu Krockenberger

Technische Universität München, Germany(Nov. 02 – May 03)

Marcus Steiner

Universität Hamburg, Germany(Jan. – Jun. 03)

Sung Woo Jung

Pohang University of Science and Technology, Korea(Jan. 03 – Jan. 04)

Sandrine Buhours

Institut National Des Sciences Appliquées, France(Feb. – Jun. 03)

Nicolas Gaillard

Ecole Nationale Supérieure de Physique de Grenoble, France(Mar. – Jul. 03)

Antonio Ballestrazzi

Università degli Studi di Modena d Reggio Emilia, Italy(Mar. – May 03)

Sang-jin Kim

Chungbuk National University, Korea(Mar. 03 – Mar. 04)-11-

Japanese Students(2002 Fiscal Year)

Name

Affiliation (Period)

Koji Aizawa

Tokyo Institute of Polytechnics, Japan (Apr. 02 – Mar. 03)

Kazuya Aoki

Tokyo University of Science, Japan (Apr. 02 – Mar. 03)

Naoki Asakawa

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Shinich Amaha

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Keji Ohno

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Naoya Ohmuro

Meiji University, Japan (Apr. 02 – Mar. 03)

Takahide Ohya

Hokkaido University, Japan (Jul. 02 – Aug. 02)

Hajime Okamoto

Waseda University, Japan (Jun. 02 – Mar. 03)

Masahiro Kashiwa

Shonan Institute of Technology, Japan (Apr. 02 – Mar. 03)

Akira Kawaguchi

Osaka University, Japan (Nov. 02 – Mar. 03)

Tatsuro Kawabata

Tokai University, Japan (Apr. 02 – Mar. 03)

Toru Kanto

The University of Electro-Communications, Japan(Jul. 02 – Aug. 02)

Takatoshi Kido

Shonan Institue of Technology, Japan (May. 02 – Mar. 03)

Tetsuo Kodera

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Naofumi Kobayashi

Meiji University, Japan (Dec. 02 – Mar. 03)

Satoshi Shigemori

Shizuoka University, Japan (Jul. 02 – Aug. 02)

Hiroshi Shimizu

Osaka Electro-Communication University, Japan(May. 02 – Jun. 02)

Masafumi Shimizu

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Yoshihiro Sugio

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Daisuke Takagi

Meiji University, Japan (Apr. 02 – Mar. 03)

Tomonori Takahashi

Keio University, Japan (Apr. 02 – Mar. 03)-12-

Kuniharu Takei

Toyohashi University of Technology, Japan(Jan. 03 – Feb. 03)

Yoshinori Tani

Tokai University, Japan (Apr. 02 – Mar. 03)

Akio Tsukada

Tokyo University of Science, Japan (Apr. 02 – Mar. 03)

Yoshifumi Nishi

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Jiro Nishinaga

Waseda University, Japan (Feb. 03 – Mar. 03)

Aihiko Numata

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Shigeto Fukatsu

Keio University, Japan (Apr. 02 – Mar. 03)

Motonari Honda

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Yuki Maruyama

Toyohashi University of Technology , Japan(Jan. 03 – Feb. 03)

Shinpe Yamaguchi

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Zin Yamazaki

Toyohashi University of Technology, Japan(Jan. 03 – Feb. 03)

Michihisa Yamamoto

University of Tokyo, Japan (Apr. 02 – Mar. 03)

Hiroyasu Yokoyama

University of Tokyo, Japan (Apr. 02 – Mar. 03)-13-

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Overview of Device Physics Research
Yasuo Takahashi
Device Physics Laboratory
Large-scale device integration technologies, which have led to rapid progress in
information processing on cellar phones and portable computers, face difficulties in further
downsizing and power consumption. To overcome these problems and thereby achieve
further growth of information processing, the Device Physics Laboratory conducts researchon the fabrication of nanostructures and single electronics, which enable us to make small andultimately low-power devices. There are two approaches to achieving nanostructures: one isto refine lithographic techniques (top-down approach), and the other is self-assembly basedon the atomic structures of the substrate (bottom-up approach). We are also investigatingother methods to create nanostructures, such as carbon nanotubes.
The Si Nanodevice Research Group is investigating the operation mechanism of Si singleelectron transistors (SETs) and their circuit applications, and is seeking to establish
fabrication principles. We have already proposed and fabricated single-electron inverters,
adders and multiple-valued logic circuits, and actually demonstrated their functions. We
recently demonstrated that our Si SETs do not have any offset-charge problems, which arethought to be the most serious obstacles to the practical use of SETs. We have also succeededin making a new type of single-electron pump that enables us to transfer just a single-electron
at high temperature. To control the potential profile in nanostructure silicon suitable for SETs,
the Si oxidation process is the most important. We have investigated the oxidation
mechanism theoretically by first-principles calculations and clarified the fundamentaloxidation process. We are also doing simulations based on the proposed oxidation principle.
The Nanostructure Technology Research Group is investigating nanofabrication
techniques based on the top-down approach and methods of evaluating the fabricatednanostructures. We have achieved ultrafine resist pattern formation by improving electronbeam lithography and optimizing resist materials and processing, and demonstrated thenanometer-scale resist patterns with a high aspect ratio by using a supercritical-fluid drying
process. Recently, we clarified the origin of the line edge roughness of resist patterns, whichis the most important issue in making fine patterns. By using the developed fine-patternformation technologies, we have fabricated and demonstrated small Si SETs with a highoperation temperature. We have also succeeded in making an ultrasmall four-point probe for
conductance measurement of small structures.
The Surface Science Research Group is investigating wafer-scale control of atomic
structures and ordered nanostructure formation based on the bottom-up approach. We havedemonstrated many kinds of self-assembled nanostructures formed on Si surface bycontrolling the alignment of the surface atoms and/or local stress accumulated in the surface.
By using synchrotron radiation, we have also succeeded in in-situ observation of surface
structures during crystal growth. We recently clarified the step bunching mechanism
theoretically and proposed a new model for Ge-atom reconfiguration on the silicon surface,which are useful for controlling the ordered nanostructures. Our research on carbon
nanotubes has led to a new growth technique using microwave plasma. We also succeeded inobserving the electronic states of nanotubes by photoelectron spectroscopy and detecting thedefects by infrared spectroscopy. We have also investigated various kinds of materials andsucceeded in making ordered CdS nanostructures and InP nanowires.
The details of some of our achievements are shown in the following four pages.

-15-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Silicon Single-Electron Pump
Yukinori Ono and Yasuo Takahashi
Device Physics Laboratory
Single-electron devices (SEDs) are promising for future ultra-large-scale integrated
circuits because of their small size and ultra-low power consumption. The single-electron
pump is a member of the SED family and can transfer single electrons even when the drain
terminal is reversely biased (hence the name “pump”). Among SEDs, the pump dissipates thelowest energy and has the highest transfer accuracy. However, the presently available pumps,
which are made of metals, have some drawbacks, including a limited (< ~100 mK)
operational temperature and poor operational stability.
In order to achieve a high level of transfer accuracy, the single-electron pump commonly
employs a chain of nanometer-scaled conducting materials, called Coulomb islands, which iscomplicated and difficult to fabricate. Technology for making multiple islands in Si is still
premature. The single-electron transistor (SET), which is the simplest SED and has only one
island, cannot work as a pump because of an inherent leakage current, which fatally lowers
the transfer accuracy. However, Si technology has enabled us to fabricate, in a controlled way,
SETs operating at high temperatures with good operational stability [1].
We thus proposed a new structure for Si-based pumps, in which we utilize a hightemperature operating Si SET in combination with two ultra-small metal-oxidesemiconductor field-effect transistors (MOSFETs) sandwiching it. These MOSFETs haveextremely high off-resistance, and this makes it possible to almost completely prevent theleakage current from flowing. We have demonstrated pump operation at 25 K [2], which is
two to three orders of magnitude higher than that for the metal-based ones.
Figure 1 shows a scanning electron microscope image of the pump. Figure 2 shows draincurrent versus drain voltage characteristics measured at 25 K for 1-MHz ac gate biases. The
drain currents are quantized in units of ef at around zero drain voltage, where e is theelementary charge and f is the frequency of the voltages to the MOSFETs. In addition, achange in the polarity of the gate-voltage phase shift results in a change in the polarity of thecurrent. These data demonstrate the single-electron transfer.
The present result is the first step towards producing practical single-electron pumps.
[1] Y. Takahashi et al., J. Phys.: Condens. Matter 14 (2002) R995.
[2] Y. Ono and Y. Takahashi, Appl. Phys. Lett. 82 (2003) 1221.

gate-1(poly-Si)gate-2(poly-Si)

source
(Si)

drain
(Si)

T = 25 K

1 MHz
0.5 Positive phase shift
I = ef (=160 fA)
0.0
I = -ef (= -160 fA)
-0.5
1 MHz
Negative phase shiftgate-3
Coulomb island (Si)

Drain current (pA)

1.0

200 nmFig. 1. Electron microscope image of the pump.
-16-

-1.0
-30 -20 -10 0 10 20 30
Drain voltage (mV)Fig. 2. Current characteristics.

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Analysis of Ultrathin Resist Film
Kenichi Kanzaki, Toru Yamaguchi, Masao Nagase, and Hideo Namatsu
Device Physics Laboratory
Thinning resist film is an effective way to prevent resist pattern collapse and improve
resolution. However, the characteristics of ultra-thin resist film, 100-nm thick or less, should
strongly reflect surface and interface effects. They should be different from those of
conventional thick resist films and affect the roughness, which is the resolution determining
factor of resist patterns. Thus, an understanding of the thinning effect on resist performance isimportant in high-resolution nanolithography. We have, therefore, clarified quantitatively theresist thinning effect on the roughness and resist internal structure [1].
Ultrathin resist films (ZEP520) (10-, 30-, and 100-nm thick) were investigated by using an
atomic force microscope (AFM). Roughness at each thickness was compared by linewidth
fluctuations of delineated line patterns (designed line width of 50 nm). It was found that the
linewidth fluctuation increased with decreasing resist thickness as shown in Fig. 1. There wasa marked increase below 30 nm. To determine the cause of the increase, we investigated thethinning effect on the resist internal structure by focusing on the polymer aggregates. The
results are illustrated in Fig. 2. The aggregates appeared to be compressed and their volume
seemed to decrease with decreasing resist thickness. Owing to those change of internal
structure, the dissolubility increased with decreasing resist thickness. This indicates that thesurrounding polymers dissolve faster when the aggregate becomes compressed. Hence, thedissolubility contrast between the polymer aggregates and surroundings is enhanced bythinning, thus probably causing the increase of roughness. This study suggests that decreasing
the dissolubility contrast is important for high-resolution nanolithography using ultra-thinresist film.
[1] K. Kanzaki et al., Jpn. J. Appl. Phys. 41 (2002) L1342.
a

20
10

3.2

0
-20

Designed line
width: 50 nm

2.8

-10

0

10

20

b

20

2.6

10

2.4

0
-20

2.2
2

Height [nm]Linewidth fluctuation [nm]

3

1.8
1.6
0

20

40

60

80

100

120

Fig. 1. Resist thickness dependence oflinewidth fluctuations.

0

10

20

c

20
10
0
-20

Thickness of resist [nm]

-10

-10

0

10

Length [nm]

20
50 nm

Fig. 2. AFM images of developed resist surfaceof (a) 100-. (b) 30-, and (c) 10-nm-thick resist.
The reconstructed profiles of typical aggregate
structures for each thickness are also shown.
-17-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Electronic Structure at Carbon Nanotube Tips Studied by Photoemission
Microscopy
Satoru Suzuki, Yoshio Watanabe, Toshio Ogino, and Yoshikazu Homma
Device Physics Laboratory
Carbon nanotubes (CNTs) have attracted attention primarily because of the unique onedimensional structure, and their exotic properties such as high current flow density, highmechanical strength, and chemical inertness. A specific electronic structure is expected at thetips of CNTs, where the graphene cylinders are closed by hemispherical caps. We examined
the position dependence of the local electronic structure along the tube axes by means ofscanning photoemission microscopy (SPEM). Our results indicate that a density of states near
the Fermi level at tips is much larger than that at sidewalls.
Figure 1 shows the C1s SPEM image of multi-walled CNTs aligned perpendicularly on a
Si substrate. The heights of the tips are almost uniform because the lengths of the CNTs arevery similar and the CNTs are well aligned. Valence band spectra of the CNTs obtained fromthe spatially selected regions (denoted by numbers in Fig. 1) are shown in Fig. 2. The spectrafrom the sidewalls of the CNTs are reasonably similar to each other and show a very small
density of states at the Fermi level. On the other hand, the two tip positions show asubstantially larger density of states near the Fermi level. It has been theoretically predictedthat such a larger density of states is formed by the insertion of 6 five-member rings into
graphene network at tips. However, in this case, the five/six member ring ratio at the tips canbe estimated to be about 1/4500 from a geometrical consideration. Thus, the contribution of
the five-member rings should be negligible. These results strongly suggest that the CNTs do
not have atomically close-packed structures, but have many structural defects (dangling
bonds), especially in the tip region. The electronic properties of the CNTs seem to besignificantly influenced by the defects, because intrinsic density of states at the Fermi level of
CNTs is generally quite small.
[1] S. Suzuki et al., Phys. Rev. B 66 (2002) 035414.

tip
1

7

2
3

CNT
4
8
5
6

2 µm

Fig. 1. C1s SPEM image of aligned
CNTs.

Fig. 2. Valence band spectra of CNTs
obtained from spatially selected
regions. The positions of themeasurements are shown in Fig. 1.
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Anisotropic Strain for Controlled Growth of Nanostructures
Koji Sumitomo, Zhaohui Zhang, Hiroo Omi, and Toshio Ogino
Device Physics Laboratory
Nanostructure self-assembly is expected to be one of the key techniques in the bottom-up
approach to realize futuristic semiconductor nanotechnology. In order to utilize the selfassembly process in Si integrated systems, however, it is important to control the fluctuations
in size, shape, and position of such nanostructures. Here, we report that the anisotropic
surface stress and strain relaxation of the 3D islands lead to elongation of the islands.
Si(113) covered with 2-ML Ge forms the stable 2×2 reconstructed surface. Figure 1
shows the 2×2 structural model we proposed and scanning tunneling (STM) images(experimental and simulations) [1]. The rows indicated an A-type are attributed to rebonded
atoms due to removal of the topmost Ge atoms and the B-type row to tilted pentamers of fiveGe atoms surrounding an interstitial atom at the subsurface. The simulated STM images
based on an optimized structure from the first-principles calculations are in good agreementwith the experiments. We also found that anisotropic surface stress resulting in such uniquesurface reconstruction plays a crucial role in nanostructure formation after further Ge
deposition. The elongation of 3D islands along [33 2 ] is energetically favorable because oftensile stress in spite of the 4% larger lattice constant of Ge than Si. Once the nanowires
begin to form (Fig. 2), the strain inside the nanowire is relaxed across the wire and leading tostability [2]. Strain field generates long-range repulsive interaction between the Ge nanowires
and results in uniform spacing between the wires. These results suggest the possibility ofatomically precise control of the shape, size, and position of nanostructures by controlling
anisotropic stress and strain.
[1] Z. Zhang et al., Phys. Rev. Lett. 88 (2002) 61011.
[2] K. Sumitomo et al., Phys. Rev. B 67 (2003) 35319.

Fig. 1. Ge/Si(113)-2×2 structural model we proposed and
STM images (a,b) experiment and (c,d)
simulation.
-19-

Fig. 2. STM image for Ge
nanowires.

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Overview of Materials Science Research
Hideaki Takayanagi
Materials Science Laboratory
The Materials Science Laboratory (MSL) aims at producing new materials to discoverquantum phenomena for new functions. The materials including those that do not exist innature are produced by controlling the configuration and coupling of atoms and molecules.
To accomplish these goals from different perspectives the following four MSL groups areformed. They cover research fields of various materials ranging from inorganic matter, suchas semiconductors, to organic matter, such as neurotransmitters. The characteristic feature of
MSL is the effective sharing of the unique nanofabrication and measurement techniques ofeach group. This enables fusion of research fields and techniques, which leads to innovative
material research for the IT society.
Molecular and Bio-Science Research Group
Create new organic materials by manipulating single molecules, and investigate information
processing devices based on neural functions.
Superconducting Thin Films Research Group
Study high-Tc superconductors by fabricating top quality samples through the molecularbeam epitaxy(MBE) method and develop its applications to microwave communication.
Superconducting Quantum Physics Research Group
Investigate theoretical and experimental research on a quantum computers superconductors
and new magnetic devices using quantum dot arrays.
Spintronics Research Group
Aim to control the spin degrees of freedom in semiconductors to achieve new device
functions for the next generation electronics.
The following are four major results obtained in the fiscal year 2002.
1. The response of the neural circuit grown from rat brain neuron is measured by means of
unique microelectrode arrays with newly developed stimulation technique that guarantees
excellent reproducibility. The obvious correlation between stimulus pattern and the
response infers that the brain memory is based on neural level mechanism.
2. First growth of Nd2CuO4-type structured La2CuO4 succeeded, which has been known as
K2NiF4-type only since low temperature growth is difficult without our MBE technique.
The growth parameters to choose each structure are fully investigated.
3. Plaquette super lattice formed by InAs quantum wires embedded in InGaAs substrates ispredicted to be a superconductor at the transition temperature 2 times higher than that ofsimple square lattice. The difference is large enough to be observed experimentally. Thisshows that material property can be designed by controlling dot structural parameters.
4. Modification of Rashba spin-orbit interaction strength in InGaAs quantum wells isobserved as a function of structural asymmetry. The interaction coefficients firstsystematically obtained by measuring magnetic resistance show good agreement to thetheoretical values.

-20-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Plasticity in Neuronal Networks
Yasuhiko Jimbo, Nahoko Kasai, Chunxi Han, and Keiichi Torimitsu
Materials Science Laboratory
It is widely accepted that synaptic plasticity is one of the major candidates for learningand memory in biological systems. In the central nervous system, where sparse coding is the
key for information processing, the mechanisms for integrating these synaptic changes arestill unknown. Here we developed cultured neuronal networks on microelectrode-array(MEA) substrates. Combining MEA based recording of neuronal activity with the novel
multi-site electrical stimulation system [1], highly reliable evoked response recording wasachieved. Using this system, we studied activity-dependent modification of evoked
responses in cultured rat cortical neuronal networks.
Cultured cortical networks showed strong spontaneous activity. Its characteristics arehighly dependent on the developmental stages [2]. To detect activity-dependent changes
accurately, we used stable mature networks cultured for more than two months. The cellplated MEA was kept in the CO2 incubator. The electrical recording/stimulation system andthe medium perfusion system were directly connected to the MEA in the incubator. Using
continuous perfusion at a quite slow rate (0.1 ml/h), the neurons could be maintained at a
steady state for some weeks. Figure 1 (a) shows the cultured neurons on the MEA. We cansee that a number of neurons extended their neurites, and connected one another. Constantelectrical stimulation was applied from a specific site and the evoked responses wererecorded. The stimulus was applied every ten seconds. A single session consisted of 360
trials and total three sessions were carried out. Fifty three neurons could be identified by
spike sorting. The evoked responses of one of the 53 neurons are shown in Fig. 1 (b) as rasterplots. A certain temporal structure gradually emerged, which indicated that the reliability ofthe evoked response of this neuron increased. Modifications in the evoked responses of theother neurons were not uniform but we found a common rule underlying these changes.
[1] Y. Jimbo et al., IEEE Trans. Biomed. Engng. 50 (2003) 241.
[2] T. Tateno et al., Phys. Rev. E 65 (2002) 051924.

Fig. 1. (a) Cultured cortical networks on an electrode-array substrate(b) Gradual modification of evoked responses induced by repetitive electrical stimulation-21-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Artificial Coordination Control in Copper Oxides by Molecular Beam
Epitaxy– New Strategy for Material Synthesis –Akio Tsukada and Michio Naito
Materials Science Laboratory
The rare-earth (RE) copper oxides of general chemical formula RE2CuO4 are known to beparent compounds of prototype high-Tc superconductors. They take two different crystal
structures: K2NiF4 (6-fold Cu-O coordination) and Nd2CuO4 (4-fold) as shown in Fig. 1. The
former accepts only hole doping, the latter only electron doping. The radius of RE3+ ionsprimarily determines which of the two structures forms. The K2NiF4 structure forms withlarge La3+ ions, while the Nd2CuO4 structure forms with smaller RE3+ ions, such as RE = Pr –Gd. Because of the thermal expansion mismatch between ionic RE-O and covalent Cu-O
bonds, however, Nd2CuO4-type La2CuO4 is predicted to stabilize below around 425ºC [1].
There have been a few attempts by bulk synthesis to stabilize Nd2CuO4-type La2CuO4 in thepast [2]. However, a conventional solid-state reaction method requires a firing temperatureof at least 500ºC, so it could not produce single-phase Nd2CuO4-type La2CuO4. We
demonstrate that low-temperature molecular-beam epitaxy indeed crystallizes La2CuO4 in the
Nd2CuO4 structure [3].
Figure 2 shows the phase diagram on the selective stabilization of the K2NiF4 structure(white) versus the Nd2CuO4 structure (gray). The vertical axis is the growth temperature andthe horizontal axis is the substrate lattice constant (a0). This is the first demonstration of
artificial coordination control in copper oxides, which may open up the next strategic material
search.
[1] A. Manthiram and J. B. Goodenough, J. Solid State Chem., 92 (1991) 231.
[2] F. C. Chou et al., Phys. Rev. B, 42 (1990) 6172.
[3] A. Tsukada, T. Greibe, and M. Naito, Phys. Rev. B, 66 (2002) 184515.
(a)

(b)

Fig. 1. Crystal structures of RE2CuO4.
(a) K2NiF4 structure, (b) Nd2CuO4 structure.
-22-

Fig. 2. Phase diagram of stabilized
crystal structures of La2CuO4.
The gray areas indicate that the La2CuO4
is stabilized in the Nd2CuO4 structure.

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Design of Superconductor in Quantum Dot Superlattices
Hiroyuki Tamura and Hideaki Takayanagi
Materials Science Laboratory

Tc

0.06
80mK

a

b

Tc [units of (t +t )/2]

The electronic properties of solids are closely related to their crystal structure which isstrictly determined by the atomic nature of the individual elements. However, the impositionof a superstructure on a given lattice makes the controlled fabrication of structures withchosen properties possible. One approach discussed more recently is to place quantum dot(QD), also known as artificial atoms, on the points of a lattice to form an artificial crystal
called a quantum-dot superlattice (QDSL) [1,2].
Here, we propose a method for forming QDSLs in a quantum wire network of square andplaquette lattices shown in Fig. 1 [3]. The plaquette lattice has a square plaquette in each unit
cell with four lattice-points at the vertices, as shown in the inset of Fig. 2. We have used thespin dependent local density approximation to obtain the band structure of the wire network.
It can be shown that both QDSLs are well represented by the Hubbard model. An interesting
difference between the two QDSLs is that the Fermi surface of the plaquette QDSL has
disconnected pieces whereas the square QDSL is formed of one piece. To find a correlation
effect that reflects both the Coulomb interaction and the structures of the Fermi surface, we
studied the existence of superconductivity for both lattices within the framework of the
Hubbard model. We found a superconducting ground state where the transition temperature
Tc of the plaquette lattice is more than double that of the square lattice as shown in Fig. 2, andis sufficiently high to allow superconductivity to be observed experimentally.
[1] H. Tamura, K. Shiraishi, T. Kimura, and H. Takayanagi, Phys. Rev. B 65 (2002) 085324.
[2] K. Shiraishi, H. Tamura, and H. Takayanagi, Appl. Phys. Lett. 78 (2001) 3702.
[3] T. Kimura, H. Tamura, K. Kuroki, K. Shiraishi, H. Takayanagi, and R. Arita, Phys. Rev.
B 66 (2002) 132508.

U =7

n = 0.85
tb = 2 − ta

0.04
60mK

a
50 nm

b

tb
ta

40mK
0.02
1.0

50 nm

ta

Plaquette

1.5

Fig. 2. Superconducting transition
temperature Tc plotted as a function of
the transfer energy ta. Tc of the plaquettelattice (ta=1.5, tb=0.5) is more thandouble that of the square lattice (ta=tb=1).
Inset: Corresponding tight-binding modelwith hopping parameters ta and tb.

Fig. 1. Diagram of a quantum wire
network with spacings a and b between
adjacent wires. We assume InAs quantum
wires buried in In0.776Ga0.224As barrier
regions. The case where a=b (a<b)
corresponds to the square (plaquette)lattice.

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Control of Spin-Orbit Interaction in a Semiconductor
Takaaki Koga and Junsaku Nitta
Materials Science Laboratory
Spin-orbit (S.O.) interaction is an important parameter responsible for the spin precession
and spin splitting in semiconductors. Therefore, its control in a semiconductor is considered
to be a key for the development of the recently growing research area, “spintronics,” where
spin degrees of freedom are explored for the realization of new device functionalities [1,2].
The so-called Rashba S.O. interaction (R.S.O.I.) is caused by the structural inversion
asymmetry (SIA) in semiconductor heterostructures, of which magnitude is controllable by
the applied gate voltages. However, the magnitude of the R.S.O.I. is generally so small that
few experimental techniques are readily available for the determination of its magnitude. In
this regard, we have been using the weak antilocalization (WAL) analysis successfully, forthe first time, for systematic and quantitative evaluation of the strength of the R.S.O.I. [3].
Shown in Fig. 1 are the potential diagrams for the four In0.53Ga0.47As quantum well (QW)
samples designed for the present investigation, where carrier supplying layers are introduced
both above and below the QW for the systematic control of the QW potential shapes. The
results of the magneto-resistance (MR) measurements of these samples at low temperatures(0.3 K) are shown in Fig. 2(a), where we find the weak localization (resistance maximum atzero magnetic field) to WAL (resistance minimum at zero magnetic field) transition as thedegree of the SIA increases. Hence, the larger the SIA of the sample, the stronger the S.O.
interaction. Shown in Fig. 2(b) are the values of the R.S.O.I. parameter α deduced from thetheoretical fitting of the MR data as shown in Fig. 2(a), together with the predicted α values
obtained from the k∙∙p perturbation calculations. We see an excellent agreement between theexperimental and theoretical α values.
[1] S. Datta and B. Das, Appl. Phys. Lett. 56 (1990) 665.
[2] T. Koga, J. Nitta, H. Takayanagi and S. Datta, Phys. Rev. Lett. 88 (2002) 126601.
[3] T. Koga, J. Nitta, T. Akazaki and H. Takayanagi, Phys. Rev. Lett. 89 (2002) 046801.

Fig. 1. Potential profiles for the
In0.53Ga0.47As quantum wells.
Solid, short-dahsed, long-dashedand dash-dotted curves denotesamples 1-4, respectively.

Fig. 2. (a) Low temperature (0.3 K) magneto-resistancedata of the quantum well samples shown in Fig. 1. ○□△▽ denote samples 1-4, respectively. (b) α values
estimated from the weak antilocalization analysis. The
inset shows the same results as in the main plot in zerofield spin splitting energy ∆0.

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Overview of Quantum Electron Physics Research
Yoshiro Hirayama
Physical Science Laboratory
Our research in the fields of quantum physics and electronics is based on semiconductor
nano-structures fabricated by high-quality semiconductor crystal growth and advanced device
fabrication techniques. We use these nanostructures to investigate quantum coherent control,
carrier interactions, and wide-bandgap semiconductor physics. Our aim is the development ofinnovative semiconductor devices. The Quantum Solid State Physics Research Group andWide-Bandgap Semiconductor Research Group are working in the following areas.
Quantum Solid State Physics Research Group(1) Carrier interactions in low-dimensional semiconductor heterostructures (carrierinteractions in bilayer systems; interactions between nuclear-spin and conduction
electrons).
(2) Quantum electronic state control in quantum dot systems (spin control & carrier dynamics
of quantum dots; fundamental properties of solid-state quantum computers).
(3) Semiconductor nano-mechanical systems (fabrication and characterization).
(4) Direct nano-scale imaging of electronic states by low-temperature STM.
Wide-Bandgap Semiconductor Research Group(1) Optical device physics in ultra-violet LEDs and optical devices using micro-facets.
(2) Electronic device physics, such as carrier transport in nitride FETs and HBTs.
(3) Impurity doping into wide-bandgap semiconductors and its characterization.
(4) Developing new semiconductor materials such as InN and diamond.
Major results obtained fiscal-year 2002 are reported in the following pages.
We have successfully carried out electrical pump and probe measurements of quantum dot
systems. We precisely measured electron relaxation time from the excited state to the groundstate and found an extremely long relaxation time when electron relaxation is accompaniedby spin flip. This means that electron spin is well separated from circumstances in a quantum
dot system. We have also succeeded in observing coherent oscillation of an electron in acoupled quantum dot. This is the first demonstration of all-electrical control of asemiconductor qubit.
We have studied interaction between a two-dimensional electron system and nuclear spins.
In a certain condition, a driving current flowing in the electron layer polarizes nuclear spins.
We have successfully demonstrated all-electrical control of nuclear spin polarization andrelaxation. In nanomechanical systems, we have fabricated InAs based mesoscopic-scalecantilevers and have found high sensitivity arising from quantum effects.
We have successfully fabricated an npn-type GaN/InGaN heterojunction bipolar transistor(HBT) using the base regrowth technique to improve ohmic characteristics. The HBTcharacteristics were drastically improved. This demonstrates that nitride HBTs are promising
for the future high-power electronic devices.
We have clarified the bandgap energy of InN, which was believed to be about 1.9 eV for
more than a quarter century. We discovered that our experimental data did not support theprevious value, so we grew a high-quality InN epitaxial layer to investigate its bandgap
energy. Then, we showed that the real bandgap energy of InN is about 0.9 eV, whichindicates that InN is a promising material for optical devices for communications.
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Long-lived Spin States in a Quantum Dot
Toshimasa Fujisawa
Physical Science Laboratory
A semiconductor quantum dot, which is often referred to as an artificial atom,accommodates tunable number of electrons that occupy well-defined orbitals. Dynamical
behaviors of electrons and electron spins in a quantum dot are growing interests for novel
spintronics devices and quantum computing applications, as well as for fundamental
characteristics of electrons and spins in nanostructures. The energy relaxation process, which
is one of the most fundamental dynamical properties, is very important for spin based
information storage (quantum bit). We successfully measured the energy relaxation time in aquantum dot and compared to the theories. The results indicate that the spin and orbital
degrees of freedom are well separated in our system. This is desirable for potential
applications to spin based information storage.
We employ novel electrical pump-and-probe measurements to investigate the relaxation
time from an excited state to the ground state in one- and two-electron semiconductor
quantum dot artificial atoms [1]. We repeatedly applied voltage pulses to push the system outof equilibrium, and measure the time-integrated non-equilibrium transient current todetermine the energy relaxation time. We find that the relaxation time of the one-electron
artificial hydrogen atom is 3 - 10 ns, which is understood by spontaneous emission of
acoustic phonons. This process can be regarded as an allowed transition in artificial atoms.
However, the relaxation time of the two-electron artificial helium atom can be longer than
200 µs, which is 4 or 5 orders of magnitude longer than that for the allowed transition. Thistransition is forbidden by total-spin conservation. Although the relaxation is actually
dominated by cotunneling process in our sample, the spin relaxation time is comparable to thetheoretical predictions based on spin-orbit coupling, indicating the high quality of our sample.
The large ratio of the allowed and forbidden transition rates indicates that the total spin is an
excellent quantum number in artificial atoms.
For the application to a spin quantum bit, in which just a single-electron spin occupy thelowest orbit in a magnetic field, the spin-orbit interactions can determine the energy
relaxation time of a spin quantum bit. We estimate from our observation that this spin
relaxation time can be longer than 1ms, which is extremely (about 9 orders of magnitude)
longer than the time required for
typical one- and two-qubit
manipulations (a few ps) [2].
Our results therefore encourage
further research in the use of thespin degree of freedom in QDs.
[1] T. Fujisawa et al., Nature
419 (2002) 278.
[2] J. Gupta et al., Science 292(2001) 2458.

Fig. 1. Energy relaxation processes in asemiconductor quantum dot.
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Compound Semiconductor Micro/Nanomechanical Devices
H. Yamaguchi and Y. Hirayama
Physical Science Laboratory
Compound semiconductor heterostructures have been used in a wide variety of opticaland electronic devices such as semiconductor lasers and ultra high-speed transistors, because
their structure dimensions can be controlled down to the nanometer scale. In particular,functionalities based on quantum mechanical principles appear with structures that havedimensions comparable to electron waves. We integrate these “quantum structures” into
microscopic mechanical structures in order to develop novel semiconductor devices. Figure 1
shows a scanning electron microscope (SEM) image of an InAs/AlGaSb displacement sensor
that is an example of such a mechanical device fabricated from a compound semiconductor
quantum structure. The single heterostructure consists of 15-nm-thick InAs and 285-nm-thick
AlGaSb layers that were released from a GaAs (111)A substrate to form a cantilever beam byusing photolithography and selective etching. The deflection of the cantilever can be detectedfrom the change in resistance, for which we obtained a sensitivity as high as 0.01 nm/Hz0.5[1]. Figure 2 shows the SEM image of another example, nanoscale InAs cantilevers, whichwere fabricated using a self-assembled growth technique. These have a thickness of 6-30 nm,
a width of 20-100 nm, and a length of 50-500 nm. InAs has the unique property of electron
surface accumulation, which enables us to fabricate conductive nanoscale cantilevers. It is
expected that the energy of such a nanoscale cantilever is quantized at low temperatures andthat such new quantum mechanical phenomena will bring about a revolution in the physics
and technology of semiconductor fine structure devices.
[1] H. Yamaguchi, S. Miyashita, and Y. Hirayama, Appl. Phys. Lett. 82 (2003) 394.
[2] H. Yamaguchi and Y. Hirayama, Appl. Phys. Lett. 80 (2002) 4428.

200 nm5µµm
Fig. 2. SEM image of nanoscale InAs
cantilevers fabricated using aself-assemble growth technique.

Fig. 1. SEM image of fabricated
InAs/AlGaSb displacement sensor.

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Nitride Heterojunction Bipolar Transistor with Regrown Base Layer
Toshiki Makimoto, Kazuhide Kumakura, and Naoki Kobayashi
Physical Science Laboratory

Collector Current (mA)A high-power microwave transistor is getting more important, since it is used for thecommunications between the base stations for cellular phones. Compared with Si and GaAs,
nitride semiconductors have high breakdown voltage due to their wide bandgap. On the other
hand, a heterojunction bipolar transistor (HBT), a kind of electronic devices, is suitable for ahigh-power microwave transistor due to its capabilities such as the high breakdown voltage,
the high current density, and the good threshold voltage uniformity. Therefore, a nitride HBTis a promising electronic device in terms of both materials and devices. However, there are
two issues to be addressed for this nitride HBT. One is a relatively lower current gain,
compared with HBTs composed of other semiconductors such as Si/SiGe and AlGaAs/GaAs.
The other is that the offset voltage in the common-emitter current-voltage (I-V)
characteristics is much higher than the value expected from the conduction-band
discontinuity between the emitter and the base layers. To solve these two issues, we haveused the base regrowth technique, resulting that the nitride HBT characteristics have been
drastically improved.
Figure 1 shows a schematic illustration of an HBT structure fabricated in this work. This
structure has two features. One is that the low resistive p-InGaN layer is used as a base layer
instead of the conventional p-GaN [1]. The other is that a double heterostructure is used toobtain a high breakdown voltage [2]. As shown in Fig. 1, many defects were produced on thebase surface during the HBT fabrication process and they are considered to degrade thenitride HBT characteristics. In this work, p-InGaN was regrown on the surface to eliminate
the effect of these defects. Figure 2 shows the common-emitter I-V characteristics at room
temperature. The maximum current gain is 2000, which is 100 times as high as the previously
reported value for the nitride HBTs [3,4]. Furthermore, the minimum offset-voltage (the turnon voltage of the collector current in the common-emitter I-V characteristics) is 0.3 V, which
is one tenth of the previously reported value [3,4].
[1] K. Kumakura et al., Jpn. J. Appl. Phys. 39 (2000) L337.
[2] T. Makimoto et al., Appl. Phys. Lett. 79 (2001) 380.
[3] T. Makimoto et al., Proceeding of The Fifth International Conference on Nitride
Semiconductors (ICNS-5), Nara Japan, May 2003.
[4] T. Makimoto et al., Proceeding of 2003 Device Research Conference (2003 DRC), Salt
Lake City USA, June 2003.

50
40
30
20
10
0

0

5

10

15

20

Collector-em itter Voltage (V)Fig. 1. Schematic illustration of an HBTstructure.

Fig. 2. Common-emitter I-V characteristics
at room temperature.
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Optical Band-Gap Energy of Wurtzite InN
Takashi Matsuoka
Physical Science Laboratory

5

2.0

4

1.5
1.0
0.5

0.0

0.5

1.0

1.5

PHOTON ENERGY (eV)2.0

Fig. 1. Squared absorbancevs. photon energy.

3

3.5

BAND-GAP ENERGY (eV)2.5

PL INTENSITY (a. u.)(ABSORBANCE)2

In the InGaAlN system we proposed [1], which has been applied for blue-green LEDs andso on, InN remains the most mysterious compound, due mainly to difficulty in growing highquality crystals because of the extremely high equilibrium vapor pressure of nitrogen. A
typical issue is the fundamental band gap Eg. Early absorption studies on poly-crystalline
films reported Eg=1.8-2.0 eV at room temperature. All of those samples showed nocorresponding band-edge photoluminescence (PL). On the other hand, based on a series ofabsorption experiments on high-quality wurtzite InxGa1-xN films, Eg decreased monotonicallyfrom 3.4 eV (x=0) to 2.1 eV (x=0.42), and it was pointed out that InN single crystals would
have a much smaller Eg than commonly believed [1]. In this report, it is described that single
crystalline InN has a band-gap energy of 0.8 eV.
High-quality wurtzite InN was successfully grown on a (0001) sapphire substrate using
metalorganic vapor phase epitaxy (MOVPE) at ambient pressure. The growth temperature
was 500ºC. Trimethylindium (TMI) and ammonia as were the source gases, and their flowrate was 1 to 6 µmol/min and 15 slm, respectively. The V/III flow rate ratio was adopted tobe large enough to suppress the indium precipitation in the film. As a carrier gas, nitrogen
was used instead of hydrogen to promote ammonia decomposition.
A typical result of the absorption at room temperature is shown in Fig. 1, which plots asabsorbance squared versus photon energy. Extrapolation of the linear region to the horizontal
axis gives Eg = 0.8-1.0 eV. In PL spectra measured at room temperature as shown in Fig. 2,
the PL peak was observed at 0.76 eV. Even under the high power excitation of 0.6 MW/cm2,
no PL was observed near the previous “band gap” energy. Eg for InGaN containing InN areplotted in Fig. 3, including InN [2]. Eg for polycrystals is larger than that for single crystals.
By fitting a quadratic curve to the data from optical absorption using least-squares method,
Eg of 0.85 eV for InN was obtained.
To conclude, the above mentioned results strongly suggest that Eg of InN should be near
0.8 eV. Precisely determining Eg of InN will require a thicker InN film of higher quality withlow carrier density. The discrepancy from previous data could be due to differences incrystallinity. Due to this work, the application field of InGaAlN is extended to infrared.
[1] T. Matsuoka et al., in: Proc. Int. Symp. on GaAs and Related Comps, Karuizawa, Japan,
1989, 141.
[2] T. Matsuoka et al., Appl. Phys. Lett. 81 (2002) 1246.
EXCITATION
LIGHT
EXCITATION
8 W/cm2

EXCITATION
0.6 MW/cm2

× 200

2
1
0

0.5

1.0

1.5

2.0

PHOTON ENERGY (eV)

2.5

Fig. 2. Photoluminescence.
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3.0

3.0

POLYCRYSTAL

2.5

[1 ]

2.0

SINGLECRYSTAL

1.5
1.0

THIS WORK [2]

0.5
0.0

0.5

1.0

INDIUM CONTENT in InGaN

Fig. 3. Bowing of band-gap
energy in InXGa1-XN.

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Overview of Quantum Optics and Optical Materials Research
Yoshiro Hirayama
Physical Science Laboratory
In the fields of quantum optics and optical materials we pursue the development of coretechnologies that will innovate optical communications and optical signal processing andseek fundamental scientific progress.
Quantum Optical State Control Research Group(1) Quantum communication and information processing (quantum cryptography/protocols,
entanglement, and computing).
(2) Atom optics (Bose-Einstein condensation of alkali atoms).
Ultrafast Optical Physics Research Group(1) High-irradiance, short-pulse soft X-ray generation from femtosecond laser-produced
plasma and its application to materials science.
(2) Ultrafast laser pulse induced terahertz radiation and its application.
Optical Device Physics Research Group(1) Optical properties in nitride-semiconductors and their device applications.
(2) Coherent control of excitonic and spin states in quantum dots.
Photonic Nanostructure Research Group(1) Photonic crystal optical circuits (2D SOI photonic crystals, organic photonic crystals, andhigher-dimensional structures).
(2) Interaction between photonic nanostructures and materials (negative refraction,
extremely-large group velocity dispersion, and photonic quasicrystal lasers)(3) Direct nanoprinting lithography
Major results obtained fiscal year 2002 are reported in the following pages.
We have carried out quantum key distribution experiments using a single-photon sourcein collaboration with a Stanford group. A single photon source, which emits exactly one
photon per pulse, is essential to completely prevent the eavesdrop action by a beam splitter.
We have demonstrated a change in the spectral shape of high-order surface harmonics at
an extreme ultraviolet wavelength by varying the spectral shape of a pump laser. We havealso observed a drastic increase in solid-surface harmonic intensity for glass targets. These
results show that active control of solid-surface harmonics is possible through pump andtarget control, which will become important for single attosecond pulse generation.
We proposed a novel structural design for an InGaN/GaN laser using a deeply etchedsemiconductor/air DBR mirrors. The optimum design for practical DBR mirrors with tilted
sidewalls is different from the conventional design using λ/(4n) semiconductor and λ/4 air.
We achieved a mirror reflectivity of 62% using the properly designed DBR structure.
We realized spot-size converters for photonic-crystal optical circuits, which enable us toefficiently couple light from conventional single-mode fibers to photonic-crystal waveguides.
This overcomes one of main obstacles for photonic-crystal circuits. We also proposed anddemonstrated novel nano-electrode lithography technique, which will be applied for various
nanostructured devices.

-30-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Quantum Cryptography Experiment Using a Single-Photon Source
Kyo Inoue
Physical Science Laboratory
Quantum cryptography, which guarantees unconditional security based on the law ofquantum mechanics, is extensively studied. It is a system that provides a secret key for
ciphering messages to two legitimate parties, utilizing the fact that non-orthogonal quantum
states cannot be fully identified by an eavesdropper. Several experiments have been
demonstrated, using attenuated laser light with an average photon number of, for example,
0.1 per pulse. However, the photon number statistics of laser light follows the Poisson
distribution, and there is a finite probability of two photons in one pulse, from which aneavesdropper can steal a part of information. It is known that the amount of leaked
information is larger for larger transmission loss. Thus, experiments using a single-photon
source, that emits no more than two photons per pulse, are desired for long-distance systems.
We successfully demonstrated a quantum cryptography experiment using a single-photon
source for the first time.
The photon source was an InAs semiconductor quantum dot fabricated at Stanford
University. In order to extract photons efficiently, the dot was embedded in a post-shaped
microcavity (Fig. 1). When illuminated by pump pulses, it emitted one photon per pulse via
spontaneous emission between particular energy levels. The emission efficiency was 6 %, andthe probability that it emitted two photons per pulse was one tenth of conventional laser light.
Using this light source, we carried out an quantum cryptography experiment based on theuncertainty among four polarization states (called BB84), and obtained desired correlation
between the transmitter and receiver with an error rate of 2.5 %. Then, applying error
correction and privacy amplification to these data, we successfully created an unconditionallysecured secret key for ciphering messages. The final key creation rate was 25 kbit/s. We also
carried out the same experiment for various channel losses between the transmitter andreceiver both for our single-photon source and a laser source (Fig. 2). The results showed that,though the key creation rate was lower in the low loss region because of the low emission
efficiency, the single-photon source could achieve longer transmission distance than laser
light.
[1] E. Waks et al., Nature 420 (2002) 762.

1µµm

Key creation rate (kb/s)

10

4

laser light

10

2

10

0

10

-2

single-photons

10

20

30

channel loss (dB)
Fig. 1. Single-photon source.

Fig. 2. Key creation efficiency as a function ofchannel loss.
-31-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

High-order Harmonic Generation from Surface Plasma
Tsuneyuki Ozaki, Atsushi Ishizawa, and Hidetoshi Nakano
Physical Science Laboratory
Coherent soft x-ray sources are indispensable tools for the development of novel
technologies related to generation and control of attosecond pulses and nanometer resolution
observation. Accordingly, many institutions throughout the world are now working
energetically for their realization, using various schemes such as x-ray lasers and high-orderharmonic generation. In the present work, we investigate a novel method called solid surface
harmonic generation, and try to achieve breakthrough in this field using targets with novel
characteristics and surface structures.
First we observed the surface harmonics spectrum in the extreme ultraviolet (XUV)
region. The pump laser is a terawatt Ti:sapphire laser (55 fs pulse width, 4×1016 W cm-2
peak intensity, P-polarized), and is focused onto silicon wafer targets at an incidence angle of
45º using off-axis paraboloid. Fig.1 shows the time-integrated XUV spectrum observed in the
specular direction of reflection. (a) is the spectrum observed for pump laser with a smooth
spectral profile, while (b) is for that observed using pump laser with a similar spectrum butwith an additional narrow spectral component. High-order harmonics corresponding to the
14th through 16th order of the 790 nm wavelength fundamental is clearly observed. The
narrow spectral component of the fundamental is also reflected in the harmonics shown in (b),which indicates that these spectra are actually harmonics.
We have also observed a new phenomenon, where the second-order harmonic intensity
drastically increases for certain target material. Fig.2 shows the integrated second harmonic
intensity observed using Pyrex glass and aluminum deposited targets, both with a surface
flatness of λ/4. Surprisingly, the second harmonic intensity from Pyrex targets are more than
two-orders of magnitude larger than that observed using aluminum mirror. The second
harmonic intensity tends to show large shot-to-shot variation with Pyrex targets, anddisappears completely when using S-polarized pump lasers. We presently attribute thisphenomenon to the effects of preplasma scalelength produced on the target surface by
prepulse or pedestal.
4000

100 (a)Intensity [arb.units]

Intensity [arb.units]

120

14

80
16

15

60
40

(b)

3000

Pyrex

2000
Al Mirror

1000

20
45

50

55

0

60

360

Wavelength [nm]Fig. 1. XUV harmonic spectrum observed
using silicon wafer target.

380 400 420 440
Wavelength [nm]460

Fig.2. Second-order surface harmonics observed
using Pyrex and aluminum mirror targets.
-32-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

High Reflective Distributed Bragg Reflectors Using a Deeply-Etched
Semiconductor/Air Grating for InGaN/GaN Laser Diodes
Tadashi Saitoh, Masami Kumagai, Hailong Wang, Takehiko Tawara, Toshio Nishida,
Testuya Akasaka, and Naoki Kobayashi
Physical Science Laboratory

1.4
2

100
90
80
70
60
50
40
30
20
10
0
90

Threshold pump intensity (MW/cm )Reflectivity (%)

InGaN/GaN lasers are attracting a great deal of attention as blue-violet light sources forthe next generation of storage systems such as the Blu-ray Disc. However, the operating
current of InGaN/GaN lasers is much higher than that of conventional GaAs/AlGaAs or
GaInAsP/InP lasers. One reason for this high threshold is their low facet reflectivity of only
about 18%, which results from the low refractive indices of GaN-based materials of about
2.5. The lifetime of InGaN/GaN lasers is strongly dependent on the operating current, whichmust therefore be reduced. To achieve this, multiple dielectric films are usually coated on thefacets, but this adds extra processing steps to laser fabrication. A promising alternative
structure for laser mirrors is a deeply etched distributed Bragg reflector (DBR)[1].
We have achieved high reflectivity by deeply etched InGaN/GaN DBR mirrors with tilted
sidewalls, which are appropriately designed by using the finite-difference time-domain
method[2] (Fig.1). The predicted optimal structure is different from the simple design
consisting of a λ/(4n) semiconductor and λ/4 air. If the sidewall of the grating is tilted by 4º,
the reflectivity of the DBR mirrors decreases to less than 40% (dashed line, dotted line).
However, any degradation in the reflectivity of a perfectly vertical sidewall can be suppressedto just a few percent even with a sidewall tilt of 4º, if the DBR structure is properly designed(solid line). We fabricated InGaN/GaN multiple-quantum well lasers based on the optimal
design. The devices operate as lasers with optical pumping at a lower threshold than devices
without DBR mirrors. The DBR mirror reflectivity is characterized by the relation between
the threshold pump intensity and the inverse of the cavity length, resulting in a highreflectivity of 62% (Fig. 2).
[1] H. Wang et al., Jpn. J. Appl. Phys. Part 2, 41 (2002) L682.
[2] H. Wang et al., Appl. Phys. Lett., 81 (2002) 4703.

Optimal structure
Wsc-top = 0.2 µm
Wsc-act = 0.2 µm

89

88
87
86
85
Sidewall angle (degree)

84

Fabry-Perot
1.2

1.0

0.8

0.6

Double sided
DBR
1

2

3

4

5

6

7

-3

1 / Cavity length (10 /µm)

Fig. 1. Dependence of reflectivity on sidewall angle.

-33-

Fig. 2. Dependence of threshold pumpintensity on inverse cavity length.

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Spot-Size Converter of Photonic Crystal Waveguide
Akihiko Shinya, Eiichi Kuramochi, and Masaya Notomi
Physical Science Laboratory(in collaboration with T. Tsuchizawa, T. Watanabe, T. Shoji, and K. Yamada in NTT
Microsystem Integration Laboratories)
Photonic crystal having a photonic band gap is expected to one of possible candidates forbasic platform of future ultra-small photonic large-scale integrated circuits, and we have been
investigating two-dimensional photonic crystals fabricated from SOI (silicon-on-insulator)
substrates. We have already realized single-mode waveguides that operate within thephotonic band gaps, and demonstrated their exotic dispersion characters [1,2]. The mode sizeof these waveguides is extraordinarily small, which is one of main reasons why ultrasmall
circuits are possible, but it has been pointed out that it is too small to effectively couple thelight to ordinary photonic transmission systems, such as optical fibers. In fact, the couplingloss between photonic crystal waveguides and single-mode fibers is larger than 30dB, whichis unacceptable for practical application.
To solve this problem, we have realized photonic-crystal waveguides incorporating spotsize converters, in collaboration with NTT Microsystem Integration Laboratories. They are
consisting of three parts, namely photonic crystal waveguides, Si-wire waveguides, andpolymer waveguides, and the boundaries between these parts have adiabatic spot-size (ormode-profile) converting regions, as shown in Fig. 1. The ultrasmall mode in the photonic
crystal waveguide is adiabatically transformed to that in the Si-wire, and then to that in thepolymer waveguide that has a spot size comparable to that of a single-mode fiber. We havedirectly measured and confirmed that the coupling loss of this structure is just 3-4dB, which
is far better than that without spot-size converters [3]. This result is a very important step
towards future application of photonic crystals, but also important for current research of
photonic crystals because it enables us to do various optical measurements which had beenpractically impossible due to inherent large coupling loss.
[1] M. Notomi et al., Phys. Rev. Lett. 87 (2001) 253902.
[2] M. Notomi et al., IEEE J. Quantum Electron. 38 (2002) 736.
[3] A. Shinya et al., SPIE Photonics West 2003, 5000-21, San Jose, USA. (2003).

MPC

SSC

Si-wireFig. 1. Schematic view of a spot-size conveter for photonic crystal waveguide (left), andelectron micrographs of the adiabatic tapers in this device (right).
-34-

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

International Symposium on Carrier Interactions and Spintronics in
Nanostructures
The symposium was held March 10-12, 2003, at the NTT Atsugi R&D Center incollaboration with New Energy and Industrial Technology Development Organization(NEDO) and Core Research for Evolutional Science and Technology (CREST) sponsored by
Japan Science and Technology Corporation (JST).
Carrier interactions are receiving strong interest due to their possibility for novel anddream devices, such as solid-state quantum computers. Spin is the most important factor
determining the carrier interactions in solid-state systems and spin-electronics (spintronics)
have been extensively studied. Research on the coherent control of charge and spin has also
progressed very rapidly. To further enhancing these studies, this symposium was organized by
Dr. Yoshiro Hirayama (Executive Manager) and Dr. Junsaku Nitta (Group Leader) of NTT
Basic Research Laboratories especially putting emphasis on carrier interactions andspintronics. NTT Basic Research Laboratories leads these fields, and the symposium aspired
to gather leading scientists in these fields and discuss the most recent topics.
On the 10th, after opening and welcoming remarks by Dr. Sunao Ishihara, Director of
NTT Basic Research Laboratories, Prof. D. D. Awschalom (UCSB) and Prof. K. H. Ploog(Paul-Drude Institute) gave plenary lectures on spin manipulation of electrons and nuclears insemiconductors and on ferromagnetic-semiconductor heterostructures, respectively. There
were nine oral presentations on nano-materials, heterostructures, and spintronics. And there
were 23 poster presentations.
On the 11th, the 15 oral presentations discussed nano-wires, spin-related phenomena,
nanomechanics, nanoprobing, quantum Hall effects, and quantum information processing.
Single photon emission was discussed by the Stanford University group and two-qubit
operation of superconductor charge qubit was reported from the NEC group.
On the 12th, there were nine oral presentations on superconductor proximity effects,
diluted magnetic semiconductors, and quantum information processing. The first
demonstration of a semiconductor charge qubit was reported by an NTT group. There were 24
poster presentations on that day.
There were totally 162 participants [including 69 from NTT]. All participants greatly
enjoyed the high-quality presentations and discussions on carrier interactions and spintronics.

-35-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Workshop on Surface & Nano-Science in NTT
An International Workshop on Surface & Nano-Science was organized by NTT and washeld on November 29, 2002, at the NTT Atsugi R&D Center. This workshop was a satellite to
the 2nd International Workshop on Nano-Scale Spectroscopy and Nanotechnology, which washeld in Tokyo. This satellite workshop covered a whole range of aspects of nanoscience andnanotechnology including various spectroscopic methods employed to understand nanoscale
phenomena. There were 51 participants (14 (overseas), 17 (domestic), 20 (NTT) ). Although
the workshop was rather short, leading scientists discussed their most recent topics intensely.
Dr. S. Ishihara, Director of NTT Basic Research Laboratories, gave the opening address
and welcomed the participants. This was followed by interesting presentation by Dr. M.
Kiskinova, Sincrotrone Trieste, and Dr. G. Salviati, IMEM-CNR in Parma. They described
their recent progress in the area of nano fabrication and their spectroscopic characterizations.
From NTT, there were 4 presentations; discussing topics such as the self-assembly ofnanostructures and interconnection, synchrotron radiation based materials science,nanolithography for nano-device fabrication, and coherent control in semiconductor
nanostructures for semiconductor quantum computers. In addition, we arranged a lab tour andparticipants had a unique opportunity to see some of the important R&D activities in thiscenter.

Science Plaza 2002
“Science Plaza 2002”, the annual open house event of NTT Basic Research Laboratories
was held on August 30, 2002, at the NTT Atsugi R&D Center.
After the opening remarks by Dr. Sunao Ishihara, the director of NTT Basic ResearchLaboratories, the “Symposium session” was held. In the symposium, there were three talks
from the fields of physical science, device physics, and material science. The “Poster session”
consisted of 41 presentations, which was followed by lively discussions. The “Laboratory
tour” gave the participants an opportunity to see the equipments and various research facilities.
In addition, major research findings were presented as a movie in the “Video theatre”. At the
party held after all the presentations, we enjoyed Japanese drum performance and promoted
mutual friendship with the participants.
There were 218 participants. We would like to thank all the participants of “Science Plaza
2002” for their fruitful discussion and comments.

-36-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Award Winner’s List (Fiscal 2002)

Y. Homma“Development of
ultrahigh vacuum in situ
scanning electron microscopeand its application to thestudy of crystal growth
processes”

May 14,
2002

H. Namatsu“Development ofSupercritical Dryer for
Ultra-fine Patterning”

Dec. 4,2002

The Japan Society ofApplied Physics
Young Scientist Awardfor the Presentation of
an Excellent Paper

K. Kanzaki“Effect of Resist Thickness
on the Linewidth
Fluctuations”

Sept. 24,2002

23rd Int. Conf. on Low
Temperature Physics
POSTER AWARD

E. Huefeld
T. Bauch
V. Krasnov
P. Delsing
H. Takayanagi“Critical Current
Distributions in Ballistic
Andreev Junctions”

Aug. 27,
2002

Japanese Society ofElectron MicroscopyAward (Setoh Award)

The prize of the Japan
Society for the
Promotion of theMachine Industry in
2002

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

In-house Award Winner’s List (Fiscal 2002)

NTT R&D Award

N. Kobayashi
T. Nishida
T. Makimoto
N. Maeda
M. Kasu
K. Kumakura"Research on Crystal Growth andBand Engineering of Nitride
Semiconductors"

Feb. 12,
2003

Award forAchievements by
Director of Basic
Research
Laboratories

N. Kasai
Y. Jimbo
K. Torimitsu
Y. Furukawa“Effect of Magnesium on Neuronal
Processing”

Mar. 20,
2003

Award forAchievements by
Director of Basic
Research
Laboratories

T. Fujisawa
Y. Tokura“Measurement of Carrier Dynamics
in Quantum Dots”

Mar. 20,
2003

Award forAchievements by
Director of Basic
Research
Laboratories

H. OmiK. Sumitomo
D. J. Bottomley“Control of Nanostructure
Self-Organization through Strain
Engineering”

Mar. 20,
2003

K. Prabhakaran“Ultrafine and Well-Defined
Patterns on Silicon ThroughReaction Selectivity”
Advanced Materials Vol. 14, 1418
(2002)

Mar. 20,
2003

T. Matsuoka“Optical Band-Gap Energy of
Wurtzite InN”
Appl. Phys. Lett. Vol. 81, 1246
(2002)

Mar. 20,
2003

Proposal of the Word “Resonant
Communication” -Vision for a New
Optical Generation

Mar. 20,
2003

Award for
Excellent Papers by
Director of Basic
Research
Laboratories
Award for
Excellent Papers by
Director of Basic
Research
Laboratories“Resonant” Award by
K. Suzuki
Director of Basic
Research
K. Furukawa
Laboratories-38-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

List of Visitor’s Talks (Fiscal 2002)

l. Device Physics
Date

SpeakerMay

16 Dr. Toshiaki Munakata

May

23 Prof. T. GustafssonMay

28 Prof. Takanori Koshikawa

Sept.

3 Prof. Adarsh Sandhu

Sept. 20 Prof. Zhaohui Zhang

Sept. 20 Mr. Florian Meneau

Oct.

1 Dr. Mark Baxendale

Oct.

9 Mr. Kosuke Tatsumura
Dr. Takanobu Watanabe

Dec.

5 Prof. E. Bauer

Dec.

18 Dr. Bingqing Wei

Affiliation"Topic"RIKEN“Time-resolved photoemission microspectroscopy
based on fs-VUV laser light”
Rutgers University (State University of New Jersey),
USA“Medium energy ion scattering studies of thin films
for microelectronic applications”
Osaka Electro-Communication University“Present status and future prospects of surface
studies by LEEM and PEEM”
Tokyo Institute of Technology“Room temperature magnetic imaging of
ferromagnetic domains by scanning micro-hall probe
microscopy”
Peking University, China“Structure transition of Ge/Si(113) surfaces during
Ge epitaxial growth”
Royal Institution of Great Britain, UK“Real-time observation of CdS nanoparticle
Synthesis”“Self-organization of CdS nanoparticles on silicon”
University of London, UK“The physics and applications of carbon nanotubes”
Waseda University“Large-scale modeling of SiO2/Si interface atomic
structures by molecular dynamics”
Arizona State University, USA“LEEM and XMCDPEEM Studies of MX layers on
semiconductor surfaces (M=Ga, Mn, X=N, As)”
Rensselaer Polytechnic Institute, USA“Tailoring and modification of carbon nanotube
architectures-39-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

March 26 Dr. Philip J. Poole

National Research Council, Canada“Growth of InAs/InP nanostructures by selective
area CBE”

ll. Materials Science
Date

Speaker

April 17 Dr. Kuniaki Amemiya

May

24 Dr. Y. LinMay

27 Dr. Simon Pedersen

June

21 Prof. Shintaro Nomura

Aug. 12 Dr. F.J. Jedema

Aug. 15 Dr. L.M.K. Vandersypen

Aug. 23 Dr. Takahiro Seki

Aug. 28 Dr. Marija Drndic
Sept.

2 Dr. Lambert Alff

Sept. 20 Dr. Thomas Schaepers

Affiliation"Topic"The University of Tokyo“Observation of intracellular boron distribution
using Boron Neutron Capture Therapy: BNCT”
SUNY at Stony Brook, USA“Magnetotunneling in an electron-hole system”
Chalmers University of Technology, Sweden“Competition of phase-breaking and thermal
broadening in few-mode mesoscopic rings”
Tsukuba University“Photoluminescence spectroscopy of semiconductor
quantum dot arrays”
University of Groningen, The Netherlands“Spin transport and spin precession in mesoscopic
metal spin valve devices”
Delft University of Technology, The Netherlands“Spin qubit experiments - from room temperature
nuclei to mK electrons”
Nagoya University“Formation of hydrophobic polysilane monolayer onwater surface assisted by liquid crystal molecules”
Massachusetts Institute of Technology, USA“Transport in CdSe nanocrystal solids”
Walther-Meissner-Institut and Technische
Universitaet Munichen, Germany“Electron-doped high-Tc superconductors: pairing
symmetry and pseudogap as viewd from grainboundary Josephson junctions”
Institut fuer Festkoeperforschung
Forshungszentrum Juelich, Germany“Quantum structures based on InGaAs/InP layer
systems: quantum wires and Josephson junctions”-40-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Oct.

9 Dr. Masumi Yamaguchi

Nov.

15 Dr. Wenping Hu

Nov.

28 Dr.Tobias Nyberg

Dec.

5 Dr. Irinel Chiorescu

Jan.

29 Prof. B. Altshuler

March 7 Dr. Cristian Urbina

Kyoto University“Sound velocity and attenuation in nuclear-orderedsolid 3He”
Stuttgart University, Germany“Organic light-emitting diodes and field-effecttransistors”
Linkopings Universitet, Sweden“Nano and micro patterned organic devices - fromneural interfaces to optoelectronic devices”
Delft University of Technology, The Netherlands“Coherent quantum dynamics of a superconducting
flux-qubit”
NEC Laboratories America & Princeton University,
USA“Dephasing of interacting electrons”
CEA-Saclay, France“Steering the quantum state of an electrical circuit”

lll. Quantum Electron Physics
Date

Speaker

April 11 Prof. G. E. W. Bauer
May

8 Prof. G. E. W. Bauer

May

17 Dr. Chul HuhJune

18 Dr. Chengxin Wang

Aug. 20 Dr. Nicolas FreytagAug. 29 Dr. Maarten Wegewijs

Affiliation"Topic"Delft University of Technology, The Netherlands“AC-DC magnetoelectronics”
Delft University of Technology, The Netherlands“Elements of semiconductor magnetoelectronics”
Kwangju Institute of Science and Technology,
Korea“Chemical treatment for metal contact to n- andp-GaN”
Simon Fraser University, Canada“Growth and characterization of nitride and other
III-V semiconductors for device applications”
Max Planck Institute for Solid State Research,
Germany“Measurements of the electron spin degree of
freedom in 2D electron systems”
Institut fur Theoretische Physik A, Germany“Negative differential conductance in abenzene-molecular device”-41-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Sept.

2 Prof. Yshai Avishai

Sept. 10 Dr. Akira Kawaguchi

Sept. 13 Prof. A. AsenovOct.

1 Dr. V. Seleznev

Oct.

10 Dr. C. Fuhner

Nov.

13 Dr. Xuedong Hu

Jan.

15 Dr. M. Henini

Jan.

20 Prof. A. R. Hamilton

Jan.

22 Prof. C. H. Nam

Jan.

29 Dr. Joshua Folk

Ben Gurion University, Israel“Dynamical symmetries in Kondo tunneling throughcomplex quantum dots”
Osaka University“Magnetic properties of a one-dimensional electron
system near quantum phase transition”
University of Glasgow, UK“Nanotechnology research and nanoscale device
simulation at University of Glasgow”
Russian Academy of Sciences Novosibirsk, Russia“Rolled-up heterostructures: fabrication, properties,
applications”
University of Hannover, Germany“Kondo and Fano resonances in semiconductor
quantum dots”
Riken and University of Maryland, USA“Spin-based quantum dot quantum computing
approaches”
University of Nottingham, UK“Structural and optical properties of self-assembled
quantum dots grown by molecular beam epitaxy”
University of New South Wales, Australia“1. Macroscopic quantum coherence in bilayer
quantum Hall systems 2. Fast twin-SET readout
for semiconductor based quantum computation”
KAIST, Korea“Coherent Control of High-order Harmonics”
Harvard University and M.I.T., USA“Spin measurements in lateral GaAs quantum dots”

lV. Quantum Optics & Optical Materials
Date

SpeakerJune

25 Prof. A. A. Andreev

July

9 Prof. Y. H. Lee

Affiliation"Topic"Research Institute for Laser Physics, Russia“Femtosecond x-ray line emission from multilayer
targets irradiated by ultrashort laser pulses”
Korea Advanced Institute of Science andTechnology, Korea“Toward the ultimate light source via 2-D photonic
crystal lasers”-42-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Aug.

9 Alexandre Soujaeff

Aug.

9 Dr. Yutaka Yoshikawa

Oct.

30 Dr. B. Zhang

Nov.

5 Dr. A. V. Gopal

March 3 Prof. S. John

March 5 Dr. S. Sebban
March 20 Prof. F. Meseguer

CNRS, France“Research & Development of Quantum
Cryptography system in CNRS”
University of Tokyo“Electric distortion of BEC under off-resonant laser
light”
Stanford University, USA“Single photon emission source: fabrication of asingle quantum dot in a micropost microcavity”
FESTA“1.35µm Intersubband transition in
InGaAs/AlAs/AlAsSb”
Toronto Univesity, Canada“Photonic band gap materials: semiconductors oflight”
Ecole Polytechnique, France“X-ray sources using fs lasers at the LOA”
Universidad Politecnica de Valencia, Spain“Photonic crystal based on opals”-43-Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

Research Activities of Basic Research Laboratories in 2002
The numbers of research papers, presentations at the international conferences and applied
patents amounted to 140, 215, and 47 in Basic Research Laboratories as a whole. All numbers
according their research areas are as follows.
Research Papers Published in International
Journals (2002. 1 - 2002. 12)
Device Physics
Materials
Science
Material Science

Quantum Electron
Physics
Quantum Optics &Optical Materials
0

10

20

30

40

50

60

60

70

Number of Papers

Presentation atatInternational
Presentations
International
Conferences (2002. 4 - 2003. 3)
Device Physics
Material Science
Materials
Science
Quantum Electron
Physics
Quantum Optics &Optical Materials
0

10

20

30

40

50

Number of Presentations

Appled Patents
AppliedPatents(2002.
(2002.11--2002.
2002.12)
12)
Device Physics
Materials
Science
Material Science

Quantum Electron
Physics
Quantum Optics &Optical Materials
0

5

10

15

Number of Applied Patents

-44-

20

25

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

The major journals and the number of published papers are shown below.
General Science Journals
Name
NatureScience(IF2001)* Numbers(27.955)4(23.329)2

Specialized Journals
Name
Physical Review B
Physical Review Letters
Applied Physics Letters
Physica E(IF2001)* Numbers(3.07)
16(6.668)14(3.849)14(1.009)14(1.248)12(0.806)12(2.189)4(2.129)4(3.733)3(6.079)1(5.579)
1

Japanese Journal of Applied Physics
Physica C
Surface Science
Journal of Applied Physics
Macromolecules
Journal of The American Chemistry Society
Advanced Materials*IF2001: Impact factor 2001 （Journal Citation Reports, 2001）

The average impact factor for individual research papers from all NTT Basic ResearchLaboratories is 3.53.
The major international conferences and their number of presentation are shown below.
Conferences

Numbers

The 23rd International Conference on Low Temperature Physics
26th International Conference on the Physics of Semiconductors
Carrier Interactions and Spintronics in Nanostructures (CISN 2003)
The 2002 International Conference on Solid State Devices and Materials
2002 Material Research Society Meeting

12
12
12
7
7

The 29th International Symposium on Compound Semiconductors (ISCS
2002)

5

Second International Conference
Bioelectronics (M&BE2)

4

on

Molecular

Electronics

and2002 International Workshop on Nitride Semiconductors (IWN2002)
Electorochemical Society Spring Meeting 2002

4
4

Conference on Laser and Electro-Optics/Quantum Electronics and Laser
Science Conference

3

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

List of Invited Talks at International Conferences (Fiscal 2002)

I. Device Physics(1) H. Kageshima, A. Taguchi, and K. Wada, “Theoretical investigation of nitrogen-doping
effect on native defect aggregation”, MRS Spring Meeting, San Francisco, USA (Apr.
2002).
(2) S. Uematsu, “Processes in silicon simulation of transient enhanced diffusion in silicontaking into account Ostwald ripening of defects”, MRS Spring Meeting, San Francisco,
USA (May 2002).
(3) Y. Takahashi, Y. Ono, S. Fujiwara and H. Inokawa, “Silicon single-electron transistors
and their applications to logic”, Electorochemical Society Spring Meeting 2002,
Philadelphia, USA (May 2002).
(4) S. Uematsu, H. Kageshima and K. Shiraishi, “Unified theory of silicon oxide growth”,
Electorochemical Society Spring Meeting 2002, Philadelphia, USA (May 2002).
(5) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi, D.
Bottomley, A. Kaneko and F. Lin, “Integration of semiconductor nanostructures andinterconnections of future self-assembled nanoarchitecture”, Electorochemical Society
Spring Meeting 2002, Philadelphia, USA (May 2002).
(6) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo and H. Omi,“Control of nanostructure self-assembly by atomic-structure and strain engineering”,
IUVSTA Workshop, Trofaiach, Austria (Jun. 2002).
(7) Y. Watanabe, S. Suzuki, T. Ogino and S. Heun, “Spectromicroscopy of carbon
nanotubes”, E-MRS, Strasbourg, France (Jun. 2002).
(8) T. Ogino, Y. Homma, Y. Kobayashi and H. Hibino, “Atomic-structure and strainengineering for control of self-organized Ge quantum nanostructures”, E-MRS,
Strasbourg, France (Jun. 2002).
(9) A. Fujiwara and Y. Takahashi, “Si nano-devices using an electron-hole system”, 5thEuropean Workshop on Low Temperature Electronics (WOLTE-5), Grenoble, France(Jun. 2002).
(10) P. Kuniyil and T. Ogino, “Synthesis of nanomagnets on semiconductor surfaces”, Int.
Conf. Comp. Eng., San Diego, USA (Jul. 2002).
(11) Y. Takahashi, Y. Ono, A. Fujiwara and H. Inokawa, “Silicon single-electron devices”,
Euro. Sol. Stat. Circ. Conf., Firenze, Italy (Sep. 2002).
(12) A. Fujiwara and Y. Takahashi, “Single-charge detection and manipulation in a Si
nanowire”, Int. Conf. on Semiconductor Quantum Dots (QD2002), Tokyo, Japan (Sep.
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

2002).
(13) Y. Takahashi, “Silicon single-electronics”, The 3rd Workshop for Terabit-level
Nano-Electronics, Cheongju, Korea (Oct. 2002).
(14) H. Kageshima, S. Uematsu and K, Shiraishi, “Si injection model for the Si thermaloxidation”, 5th Asian Workshop on First-Principles Calculation, Seoul, Korea (Oct.
2002).
(15) P. Kuniyil and T. Ogino, “Versatile functionality to silicon by nanoparticle incorporation”,
Nanoparticles 2002, New York, USA (Oct. 2002).
(16) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi and Z.
Zhang, “Strain engineering for control of Ge quantum nanostructures on Si surfaces”,
The 10th international Colloquim on SPM, Waikiki, USA (Oct. 2002).
(17) Y. Homma, H. Takenaka, F. Tojou, S. Hayashi, N. Goto, M. Inoue and R. Shimizu,“Evaluation of BN-delta-doped multilayers as the reference material for SIMS shallow
depth profiling”, The 2nd China-Japan Joint Seminar on Atomic Level Characterization,
Guillin, China (Nov. 2002).
(18) T. Yamaguchi, K. Yamazaki, M. Nagase and H. Namatsu, “Line-edge roughness:
Characterization and material origin”, MNC2002, Tokyo, Japan (Nov. 2002).
(19) S. Suzuki, Y. Watanabe, T. Ogino and S. Huen, “Photoemission spectromicroscopy ofcarbon nanotubes”, 2nd Int. Workshop on Nano-scale Spectroscopy and Nanotechnology,
Tokyo, Japan (Nov. 2002).
(20) Y. Watanabe, S. Suzuki, T. Ogino, S. Huen, L. Gregoratti, A. Barinov, B. Kaulich, M.
Kiskinova, W. Zhu, C. Bower and O. Zhou, “Electronic properties of carbon nanotubes
studied by photoemission spectroscopy and spectromicroscopy”, Int. Symp. on
photoelectron micro-PES, Tsukuba, Japan (Dec. 2002).
(21) Y. Takahashi, Y. Ono, A. Fujiwara and H. Inokawa, “Development of silicon
single-electron devices”, Nano MES 2003, Tempe, USA (Feb. 2003).
(22) P. Kuniyil, “Nanoparticles as potential candidates for bottom-up approach”, JSPS-DST
Symposium, Tokyo, Japan (Mar. 2003).

II. Materials Science(1) H. Takayanagi, R. Shaikhaidarov, A. F. Volkov, V. T. Petrashov, P. Delsing and T.
Cleason, “π - state in a S-N-S junction with a dangling superconducting arm”, FirstInternational Workshop on the Symmetry in Macroscopic Quantum States, Augsburg,
Germany (Apr. 2002).
(2) H. Takayanagi, S. Saito, H. Tanaka and H. Nakano, “Squid Qubit and its Readout”,
Euroworkshop “Quantum computers: mesoscopic implementations, perspectives andopen problems”, Torino, Italy (Jun. 2002).
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)(3) M. Naito, “Phase control of La2CuO4”, International Conference on Electronic Materials
International Conference on Electronic Materials (IUMRS-ICEM2002), Xian, China(Jun. 2002).
(4) J. Nitta, “Rashba spin-orbit interaction and its applications”, NATO Advanced ResearchWorkshop “Frontiers of spintronics and optics in semiconductors: A synposium in honorof E. I. Rashba", Boston, USA (Jun. 2002).
(5) K. Torimitsu, Y. Furukawa and H. Tabei, “Nanostructure controlled substrates: Surface
modified substrates for nerve cell growth”, 9th Int. Conf. Comp. Eng., San Diego, USA(Jul. 2002).
(6) M. Naito, A. Tsukada, T. Greibe and H. Sato, “Phase control in La-214 epitaxial thinfilms”, SPIE Annual meeting 2002, Seattle, USA (Jul. 2002).
(7) K. Torimitsu, “Analysis of brain functions and nano-bio device architecture”,
Swedish-Japanese Workshop on Bioelectronics, Sigtunastiftelsen, Sweden (Aug. 2002).
(8) A. Matsuda, T. Fujii and T. Watanabe, “Gap inhomogeneity, phase separation, and apseudogap in Bi2Sr2CaCu2O8+δ”, 23rd International Conference on Low Temperature
Physics (LT23), Hiroshima, Japan (Aug. 2002)(9) H. Takayanagi, H. Tamura, K. Shiraishi, T. Kimura, T. Akazaki and A. Richter,“Ferromagnetism and superconductivity in artificial crystals”, International Workshop on
Electron Interference and Decoherence in Nanostructures Ferromagnetism inquantum-dot array system, Dresden, Germany (Nov. 2002).
(10) Y. Jimbo, N. Kasai and K. Torimitsu, “MEA-based recording of neuronal activity”,
International Forum on Biochip Technologies 2002, Beijing, China (Nov. 2002).
(11) H. Takayanagi, S. Saito, H. Tanaka and H. Nakano, “Readout of the qubit state with a
SQUID”, 5th Sweden-Japan Joint Workshop on Quantum Nanoelectronics, Yokohama,Japan (Dec. 2002).
(12) M. Naito, S. Karimoto, K. Ueda, H. Yamamoto and J. Kurian, “MBE growth of high-Tc
superconductors - cuprates to borides”, MRS Fall Meeting, Boston, USA (Dec. 2002).
(13) H. Takayanagi, S. Saito, H. Tanaka and H. Nakano, “Readout of the qubit state with a
SQUID”, International Conference on Nanoelectronics Ferromagnetism inquantum-dot-array systems, Lancaster, UK (Jan. 2003).
(14) H. Takayanagi, S. Saito, H. Tanaka and H. Nakano, “Readout of the qubit state with adc-SQUID”, Int. Symp. on Advanced Physical Fields 8y, Tsukuba, Japan (Jan. 2003).
(15) J. Nitta, “Rashba spin-orbit interaction and spin-interference in nano-structures”,
International Workshop “Coherence in Nanosystems, Spin-related Transport in
Semiconductors”, Seoul, Korea (Jan. 2003).

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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

III. Quantum Electron Physics(1) Y. Hirayama and Y. Tokura, “Point contact conductance in backgated heterostructures”,
The Electrochemical Society, Philadelphia, USA (May 2002).
(2) T. Fujisawa, “Spin relaxation in semiconductor artificial atoms ― energy relaxation
time and nonequilibrium transport ― ”, 7th International Conference on
Nanometer-scale Science and Technology (NANO-7), Malmo, Sweden (Jun. 2002).
(3) T. Fujisawa, “Inelastic spin relaxation in a quantum dot”, 26th Int. Conf. Phys. Semicond.
(ICPS), Edinburgh, UK (Jul. 2002).
(4) Y. Hirayama, “Electrical manipulation of nuclear spin polarization by quantum Hall
states”, ERATO Workshop: Mesoscopic Correlation in Nanostructures, Delft, Holland(Jul. 2002).
(5) T. Fujisawa, “Inelastic spin relaxation and non-equilibrium transport in quantum dots”,
ERATO Workshop: Mesoscopic Correlation in Nanostructures, Delft, Holland (Jul.
2002).
(6) K. Muraki, T. Saku, and Y. Hirayama, “Charge excitation and transport in pseudo-spin
quantum Hall ferromagnets”, LT-23, Hiroshima, Japan (Aug. 2002).
(7) T. Fujisawa, “Dynamics of single-electron charge and spin in quantum dots”, Int.
Colloquium on Scanning Probe Microscopy (ICSPM10), Hawaii, USA (Oct. 2002).
(8) Y. Tokura, “Point contact conductance in backgated heterostructures”, The
Electrochemical Society, Philadelphia, USA (Oct. 2002).
(9) H. Yamaguchi, K. Kanisawa, Y. Tokura, and Y. Hirayama, “Structural and Electrical
Characterization of InAs/GaAs (111)A Heterostructures by Scanning TunnelingMicroscopy and Spectroscopy”, 2nd International Workshop on Nano-scale
Spectroscopy and Nanotechnology, Tokyo, Japan (Nov. 2002).
(10) K. Kanisawa, Y. Tokura, H. Yamaguchi and Y. Hirayama, “Scanning tunnelingspectroscopy study of zero-dimensional structures at the InAs surface”, 30th Conference
on the Physics and Chemistry of Semiconductor Interfaces (PCSI-30), Salt Lake City,
USA (Jan. 2003).
(11) K. Kanisawa, Y. Tokura, H. Yamaguchi and Y. Hirayama, “Direct probing of
local-density-of-states in semiconductor nanostructures”, Photonics West 2003, San Jose,
USA (Jan. 2003).
(12) H. Yamaguchi, S. Miyashita and Y. Hirayama, “Fabrication and characterization of
InAs-based electromechanical systems”, 2002 RCIQE International Seminar on
Quantum Nanoelectronics for Meme-Media-Based Information Technologies, Sapporo,
Japan (Feb. 2003).
(13) M. Kasu, A. Aleksov, M. Kubovic, N. Teofilov, E. Kohn, R. Sauer, N. Kobayashi, “High-49-

Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)

crystalline quality (111) homoepitaxial diamond layer grown by MOCVD”, Surface andBulk Defects in CVD Diamond Films VIII, Hasselt, Belgium (Feb. 2003).
(14) T. Fujisawa, “Single electron dynamics in quantum
Nanotechnology Colloquium, Lund, Sweden (Mar. 2003).

dots”,

Sweden-Japan

IV. Quantum Optics & Optical Materials(1) M. Notomi, A. Shinya, I. Yokohama and K. Yamada, “SOI photonic crystals andphotonic band gap waveguides”, MRS Spring Meeting, San Francisco, USA (Apr. 2002).
(2) H. Kamada, H. Gotoh, H. Ando, T. Takagahara and J. Temmyo, “Exciton rabi
oscillation : Coherently manipulate zero-dimensional quantum states by light”,
CLEO/QELS, Long Beach, USA (May 2002).
(3) M. Notomi, A. Shinya, E. Kuramochi, I. Yokohama, K. Yamada, C. Takahashi and J.
Takahashi, “Highly dispersive nature of photonic-band-gap waveguide”, CLEO/QELS
2002, Long Beach, USA (May 2002).
(4) M. Notomi, A. Shinya, E. Kuramochi, I. Yokohama, K. Yamada, C. Takahashi and J.
Takahashi, “Photonic crystal waveguide”, Opto-Electronics and Communications
Conference (OECC 2002), Yokohama, Japan (Jul. 2002).
(5) M. Notomi, “Wavelength and spatial dispersion in photonic crystals”, EOS Topical
Meeting on Two-dimensional Photonic Crystals, Ascona, Switzerland (Aug. 2002).
(6) H. Kamada, H. Ando, T. Takagahara, H. Gotoh and J. Temmyo, “Quantum mechanicaltime-evolution of exciton states in semiconductor quantum dots: Quantum gate operationof exciton qubits”, International Conference on Solid State Devices, Nagoya, Japan (Sep.
2002).
(7) H. Nakano, T. Nishikawa and K. Oguri, “Time-resolved absorption spectroscopy using
ultrashort soft x-ray pulses from femtosecond laser-produced plasma”, JST International
Symposium on Control of Molecules in Intense Laser Fields, Tokyo, Japan (Sep. 2002).
(8) H. Nakano, T. Nishikawa, K. Oguri and N. Uesugi, “Time-resolved absorption
spectroscopy using ultrashort soft x-ray pulses from femtosecond laser-produced
plasma”, JAERI Symposium on Control of Lasers for Strong Field Phenomena, Kyoto,
Japan (Sep. 2002).
(9) H. Kamada, H. Gotoh, H. Ando, T. Takagahara and J. Temmyo, “Single quantum dots
exciton : Application to quantum optics”, QD2002, Tokyo, Japan (Sep. 2002).
(10) K. Inoue, E. Waks and Y. Yamamoto, “Differential phase shift quantum key distribution”,
Photonics Asia 2002, Shanghai, China (Oct. 2002).
(11) M. Notomi, “Dispersive behavior of photonic crystals (Dispersion control and negativerefraction)”, The 4th International Meeting on Photonic and Electromagnetic Crystal
Structures (PECS IV), Los Angeles, USA (Oct. 2002).
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Research Activities in NTT Basic Research Laboratories Vol. 13 (June, 2003)(12) M. Notomi, “Wavelength and spatial dispersion in photonic crystals”, CIAR
Nanoelectronics Program Fall Workshop, Banf, Canada (Oct. 2002).
(13) M. Notomi, A. Shinya, E. Kuramochi, K. Yamada, T. Shoji, T. Watanabe, T. Tsuchizawa
and J. Takahashi, “Novel properties of photonic band gap waveguides”, The 15th Annual
Meeting of IEEE/LEOS (LEOS 2002), Glasgow, UK (Nov. 2002).
(14) H. Kamada, H. Gotoh, H. Ando, and T. Takagahara, “Quantum dot exciton Rabi
oscillation and quantum gate operation”, APF8, Tsukuba, Japan (Jan. 2003).
(15) H. Kamada, H. Gotoh, H. Ando, T. Takagahara and J. Temmyo, “Quantum gate
operation of exciton qubits in semiconductor quantum dots”, Photonics West 2003, San
Jose, USA (Jan. 2003).

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Editorial Committee
Koji Sumitomo
Tomoaki Kawamura
Satoshi Sasaki
Azusa Matsuda

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