Research Activities
in
NTT Basic Research Laboratories
Volume 12
Fiscal 2001

July 2002
NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation (NTT)http://www.brl.ntt.co.jp

Scanning electron microscopy images of singlewalled carbon nanotubes grown between Si
pillars fabricated by SOR lithography

Carbon Nanotube Interconnection
Carbon nanotubes are promising for wiring and connecting nano-scale devices because of
their peculiar mechanical and electrical properties. We have proposed a self-assembled
carbon nanotube interconnection and succeeded in fabricating a network on an array ofnanometer-scale Si pillars. (Page 15)

Qubit states and Schrödinger’s cat

Readout Characteristics
and wave functions

Quantum Computer with Superconductor
Readout characteristics of a quantum bit (qubit), which is a basic element of a quantum
computer, are studied. We fabricated flux qubit, which uses superconductor ring, andconfirmed readout distingishability between two opposite current states. The superconductor
ring is also interesting from the viewpoint of pure quantum physics and is a manifestation of
Schrödinger’s cat. (Page 20)

Imaging of Zero-dimensional States in a Semiconductor Nanostructure
Utilization of the quantum mechanical wave phenomena in nanostructures is important fordeveloping quantum devices and quantum computers. We have imaged the local density ofstates (LDOS) of zero-dimensionally confined electron waves by using scanning tunnelingmicroscopy (STM) at low temperatures. It is found that the LDOS distribution of asemiconductor nanostructure coincides with the probability distribution of electrons in a zerodimensional structure (a quantum dot). (Page 23)

(a)

(b)

+
-

SEM images of quantum dot

Coherent Optical Control of Quantum Dot Exciton Superposition
Experimental demonstration was made of coherent optical control of single-dot exciton by aphase-locked pulse train (right figure): The first pulse creates an exciton coherent
superposition that is alterd by the following pulses with phase control. Left figure (a) top
view of the InGaAs quantum dot array, and (b) cross-sectional view of an isolated structure
showing disk-shaped InGaAs region buried in Al-rich alloy. (Page 30)

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 “Informative
Ambience”. 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 material science, quantum electronic
physics, and quantum optics, and this work
engages the efforts of about one hundred
researchers. Nanotechnology designed to control nano-structures at molecular andatomic 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 on Mesoscopic Superconductivity and Spintronics
2002 in March this year.
This booklet, “Research Activities in NTT Basic Research Laboratories Vol. 12,”
provides an overview of our research activities in 2001. We hope this booklet willencourage mutual understanding and further collaboration among all scientists.
July 2002

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@will.brl.ntt.co.jp

Contents
page

Member List.......................................................................................................................... 1
I. Research Topics◆Overview of Device Physics Research............................................................................... 12♦ Single-Electron Multiple-Valued Logic♦ Mechanism of Roughness Generation in Resists♦ Carbon Nanotube Interconnection♦ Nanoparticles for Multi-functionalization of Silicon: A Plug and Play Approach◆Overview of Materials Science Research........................................................................... 17♦ Neuronal Responses in Rat Hippocampus induced by Low Magnesium♦ In-situ Growth of Superconducting MgB2 Thin Films♦ Readout of Superconductor Quantum Bit♦ Proposal of a Spin-Filter Device using Nonmagnetic Semiconductors◆Overview of Quantum Electron Physics Research ............................................................ 22♦ Imaging of Zero-Dimensional States in a Semiconductor Nanostructure♦ Pseudospin Ferromagnetic Order in Bilayer Electron Systems♦ Npn-type InGaN/GaN Nitride Heterojunction Bipolar Transistor (HBT)♦ AlGaN-based Light Emitting Diodes◆Overview of Quantum Optics and Optical Materials Research ......................................... 27♦ Quantum Magic Protocols♦ Measuring an Ultrashort Soft X-Ray Pulse Shape♦ Quantum Gate Operation of Quantum Dot Exciton Qubit♦ Photonic-Crystal Single-Mode Waveguide

II. Data◆International Symposium on Mesoscopic Superconductivity and Spintronics.................. 32◆Award Winner’s List .......................................................................................................... 33◆In-house Award Winner’s List ........................................................................................... 34◆List of Visitor’s Talks ......................................................................................................... 35◆Research Papers Published in International Journals......................................................... 40◆Presentations at International Conferences ........................................................................ 41◆List of Invited Talks at International Conferences ............................................................. 42

Member List
As of March 31, 2002(*/ 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

Senior Manager,

Dr. Tetsuomi Sogawa

Senior Research Scientist,

Dr. Fumihiko Maeda

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. Toshio Ogino
Dr. Hiroyuki Kageshima
Takeshi Karasawa

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

Dr. Masashi Uematsu
Dr. Toru Akiyama

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

Junzo Hayashi
Dr. Kenichi Kanzaki

Surface Science Research Group:
Dr. Toshio Ogino (Group Leader)
Dr. Yoshihiro Kobayashi
Dr. Yoshikazu Homma
Dr. Tomoaki Kawamura
Dr. Prabhakaran Kuniyil
Hiroki Hibino
Dr. Fumihiko Maeda
Dr. Satoru Suzuki
Dr. Krishna Gopal Nath*
Dr. Arata Kaneko
Dr. Feng Lin-2-

Dr. Yoshio Watanabe
Dr. Koji Sumitomo
Dr. Hiroo Omi
Dr. David Bottomley*

Materials Science Laboratory

Executive Manager,

Dr. Hideaki Takayanagi
Dr. Hiroyuki Shibata

Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Michiya Fujiki
Dr. Keisuke Ebata
Dr. Yasuo Suzuki
Dr. Kazuaki Furukawa
Dr. Nahoko Kasai
Dr. Yoshiaki Kashimura
Dr. Chunxi Han
Dr. Hongzhi Tang*
Superconducting Thin Films Research Group:
Dr. Michio Naito (Group Leader)Dr. Hideki Yamamoto
Dr. Shin-ichi Karimoto
Dr. Jose KurianSuperconducting Quantum Physics Research Group:
Dr. Hideaki Takayanagi (Group Leader)
Dr. Azusa Matsuda
Kouichi Semba
Dr. Hayato Nakano
Dr. Noriyuki Hatakenaka
Dr. Hiroyuki Tamura
Hirotaka Tanaka
Dr. Shiro Saito
Dr. Kenichi Matsuda
Dr. Andreas Richter
Spintronics Research Group:
Dr. Junsaku Nitta (Group Leader)
Dr. Kotaro Tsubaki
Dr. Yoshiaki Sekine-3-

Dr. Yasuhiko Jimbo
Dr. Katsuhiro Ajito
Dr. Hiroshi Nakashima

Dr. Kenji Ueda

Dr. Tatsushi Akazaki
Dr. Yuichi Harada
Dr. Takashi Kimura
Dr. Minoru Kawamura

Dr. Takaaki Koga*

Physical Science Laboratory

Executive Manager,

Dr. Takaaki Mukai
Dr. Akihito Taguchi

Quantum Solid State Physics Research Group:
Dr. Yoshiro Hirayama (Group Leader)
Dr. Yasuhiro Tokura
Dr. Hiroshi Yamaguchi
Dr. Toshimasa Fujisawa
Dr. Kiyoshi Kanisawa
Dr. David Guy Austing*
Kyoichi Suzuki
Dr. Toshifumi Itakura
Wide-Bandgap Semiconductor Research Group:
Dr. Naoki Kobayashi (Group Leader)
Dr. Toshiki Makimoto
Dr. Makoto Kasu
Dr. Yasuyuki Kobayashi
Dr. Seigo Ando
Dr. Narihiko Maeda
Yoshiharu Yamauchi
Dr. Kazuhide Kumakura
Masanobu Hiroki
Quantum Optical State Control Research Group:
Dr. Takaaki Mukai (Group Leader)
Dr. Kyou Inoue
Dr. Kaoru Shimizu
Dr. Tetsuya Mukai
Dr. Fumiaki Morikoshi
Dr. Tao Hong
Dr. Michael Wong Jack-4-

Dr. Koji Muraki
Dr. Satoshi Sasaki
Dr. Toshiaki Hayashi

Dr. Takashi Matsuoka
Dr. Toshio Nishida
Dr. Tetsuya Akasaka
Dr. Yoshitaka Taniyasu

Dr. Makoto Yamashita
Dr. Bingyang Zhang

Ultrafast Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Tadashi Nishikawa
Dr. Ryuzi Yano
Dr. Tsuneyuki Ozaki
Dr. Jingquan Lin
Optical Device Physics Research Group:
Dr. Tadashi Saitoh (Group Leader)
Hidehiko Kamada
Masami Kumagai
Dr. Hideki Gotoh
Dr. Takehiko Tawara
Photonic Nano-Structure Research Group:
Dr. Takaaki Mukai (Group Leader)
Dr. Nobuhiko Susa
Dr. Masaya Notomi
Dr. Atsushi Yokoo
Dr. Akihiko Shinya-5-

Katsuya Oguri

Dr. Shunji Nojima
Dr. Hailong Wang

Eiichi Kuramochi

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 and Materials Research Society.

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.

-6-

Distinguished Technical Member

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

-7-Advisory Board (2001 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(2001 Fiscal Year)

Name

Affiliation
PeriodProf. Michael B. Santos

University of Oklahoma, USA
March – July, 2001

Prof. Zhigang Zhang

Tianjin University, China
September– October, 2001

Dr. Hai-Du Cheong

Pohang University of Science and Technology, Korea
September, 2001– August, 2002

Dr. Takaaki Koga

Japan Science and Technology Corporation (JST), Japan
December 2001 – November, 2002

Dr. Paulo V. Santos

Paul-Drude-Institut für Festkörperelektronik, Germany
January – March, 2002

Prof. Gerrit E. W. Bauer

Delft University of Technology, The Netherlands
March – June, 2002

-9-

Trainees(2001 Fiscal Year)

Name

Affiliation (Period)

Ronald Hanson

Delft University of Technology, The Netherlands(Feb. – Apr. 01)

Elise Laffosse

Institut National Des Sciences Appliquées, France(Mar. – Aug. 01)

Jean Delmas

Institut National Des Sciences Appliquées, France(Mar. – Aug. 01)

Yingkai John Liaw

University of Illinois, U.S.A (May – Aug. 01)

Tine Greibe

Technical University of Denmark, Denmark (Jun. – Jul. 01)

Ruth Anne Child

University of Oxford, England (Jul. – Sep. 01)

Julien Derr

Ecole Supérieure de Physique et de Chimine Industrielles deParis, France (Aug. – Dec. 01)

Richard Engstrom

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

Francois Dewarrat

University of Basel, Switzerland (Nov. – Dec. 01)

Niti Goel

University of Oklahoma, USA (Jan. – Feb. 02)

Ronald Hanson

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

L. H. Willems van Beveren

Delft University of Technology, The Netherlands(Jan. – Mar. 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)-10-

Japanese Students(2001 Fiscal Year)

Name

Affiliation (Period)

Koji Aizawa

Tokyo Institute of Polytechnics, Japan (Oct. 01 – Mar. 02)

Toru Akiyama

University of Tsukuba, Japan (Jan. 02 – Feb. 02)

Shinich Amaha

University of Tokyo, Japan (Apr. 01 – Mar. 02)

Kazuya Aoki

Tokyo University of Science, Japan (Apr. 01 – Mar. 02)

Naoki Asakawa

University of Tokyo, Japan (Jun. 01 – Mar. 02)

Yusuke Asari

Waseda University, Japan (Apr. 01 – Mar. 02)

Tetsuya Asayama

University of Tokyo, Japan (Apr. 01 – Mar. 02)

Emi Hagiwara

Tokai University, Japan (Apr. 01 – Mar. 02)

Motonari Honda

University of Tokyo, Japan (Apr. 01 – Mar. 02)

Masahiro Kashiwa

Shonan Institute of Technology, Japan (Jul. 01 – Mar. 02)

Tatsuro Kawabata

Tokai University, Japan (Apr. 01 – Mar. 02)

Tomohiro Kita

Japan Advanced Institute of Science and Technology, Japan(Apr. 01 – Mar. 02)

Yoshimich Nakamura

Waseda University, Japan (Apr. 01 – Mar. 02)

Yoshifumi Nishi

University of Tokyo, Japan (Apr. 01 – Mar. 02)

Aihiko Numata

University of Tokyo, Japan (Jun. 01 – Mar. 02)

Satoshi Shigemori

Shizuoka University, Japan (Oct. 01 – Dec. 01)

Yoshihiro Sugio

University of Tokyo, Japan (Nov. 01 – Mar. 02)

Tomonori Takahashi

Keio University, Japan (Apr. 01 – Mar. 02)

Akio Tsukada

Tokyo University of Science, Japan (Apr. 01 – Mar. 02)

Masahiro Wada

Waseda University, Japan (Apr. 01 – Mar. 02)

Michihisa Yamamoto

University of Tokyo, Japan (Apr. 01 – Mar. 02)

Takayuki Yamashita

Tokai University, Japan (Apr. 01 – Mar. 02)

Hiroyasu Yokoyama

University of Tokyo, Japan (Jun. 01 – Mar. 02)-11-

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Overview of Device Physics Research
Toshio Ogino
Device Physics Laboratory
In the Device Physics Laboratory, we are studying silicon (Si) nanotechnology as a meansof creating the ultimate Si integrated devices to further the evolution of information
technology. In terms of device functions, single electron switching is the ultimate technology.
In signal transmission, the ultimate goal is single electron transfer to the nearest neighbor siteor long-distant sites. In fabrication technology, the final goal is the wafer-scale fabrication of
atomically controlled device structures. There are two approaches available to achieving thelatter: one is to refine lithographic techniques to achieve higher resolution and finer patterns(top-down approach), and the other is self-assembly based on the atomic structures of the Si
substrate (bottom-up approach). Our aim is to create new concepts towards the ultimate Si
integrated systems.
The Si Nanodevice Research Group is investigating the operation mechanism of Si single
electron transistors (SETs) and their application to logic circuits, and performing fabrication
process simulations. We have already demonstrated inverters and adders using SETs. We
recently fabricated multi-valued logic circuits and a multi-bit adder as demonstrations of thewide range of functionality in SETs. Negative differential conductance in SETs has also been
analyzed and applied to a new functional circuit. In single electron transfer devices (chargecoupled devices), we have succeeded to detect single-electron and single-hole transfer atroom temperature. Operation mechanisms of SETs are being analyzed based on a structuralmodel developed by the Nanostructure Technology Research Group. Si oxidation is the mostimportant process in Si technology. We have shown that oxidation characteristics undervarious conditions can be explained using a universal model based on an atomic-level theory
proposed by us.
The Nanostructure Technology Research Group is investigating nanofabrication
techniques based on the top-down approach. We have established an ultrafine resist patternformation process through improvement of electron beam lithography and optimization ofresist materials and processes. We have proposed an original ultrafine patterning techniquethat uses supercritical fluid. Its outstanding performance was demonstrated in resist patterns
with a high aspect ratio and ultrahigh density. A structural model of SETs fabricated in the
Nanodevice Research Group has been established.
The Surface Science Research Group is investigating a bottom-up approach, aiming for Si
nanointegration through surface structure control, nanostructure self-assembly, and carbon
nanotube interconnection. For surface structure control, we are investigating atomic structures
on step-controlled Si surfaces to control all atom positions on the surface. In nanostructureself-assembly, we have established strain engineering for control of the shape, distribution,and spacing of self-assembling Ge quantum nanostructures on Si surfaces. A new techniquefor functionalization of Si surfaces based on the incorporation of chemically synthesizednano-particles has been developed. In applications of synchrotron radiation, we havedeveloped a technique for in-situ observation of growing surfaces and photoelectron
microscopy for nanostructure characterization. During the past year, we put emphasis on our
carbon nanotube project and started NEDO International Joint Research Grant Program. We
have succeeded in bridging Si pillars by carbon nanotubes. Characterization of the electronic
and atomic structures of the carbon nanotubes has also proceeded.

-12-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Single-Electron Multiple-Valued Logic
Hiroshi Inokawa, Akira Fujiwara, and Yasuo Takahashi
Device Physics Laboratory
Single-electron devices are quite suitable for multiple-valued logic, because thediscreteness of the electronic charge in a Coulomb island can be directly related to multiplevalued operation. However, it is fairly difficult to construct the circuit only with singleelectron devices because of their low voltage gain and the small applicable voltage. To solve
this problem, we have proposed a hybrid device comprising a single-electron transistor (SET)and a MOSFET, and demonstrated the operation using devices fabricated by patterndependent oxidation (PADOX) process on a silicon-on-insulator (SOI) wafer.
The proposed device has a simple structure of a serially connected SET and MOSFET. A
MOSFET is used to keep the SET drain voltage constant at a low enough value. As a result,the current flowing through the device is determined only by the SET input voltage; it is notaffected by the output voltage. When the input and output terminals are shorted together,
multipeak negative-differential-resistance is attained as two-terminal characteristics (Fig. 1).
With a proper load device (a constant-current source in the case of Fig. 1), many stability
points appear and these can be assigned to multiple-valued levels [1].
Figure 2 shows the input-output waveforms of a quantizer, which is a basic component ofmultiple-valued logic. The input voltage is transferred to the output terminal (V in Fig. 1) at
the moment sampling pulses turn on the transfer-gate MOSFET (not shown in Fig. 1), andthen quantized to the nearest stability point. We can see that the different voltage levels in thetriangular wave are clearly quantized to stability points a ~ f.
With the proposed device, extremely compact multiple-valued logic can be constructedbecause circuit size is independent of the number of multiple-valued levels due to the periodic
nature of the SET input-output characteristics. A new application field of single-electron
devices can now be explored by the multiple-valued logic, as illustrated by an n-bit flash A/Dconverter whose size is proportional to n (in contrast to n2-1 for conventional
implementation) and an ultrahigh-speed multiple-valued adder without carry propagation [2].
[1] H. Inokawa et al., Appl. Phys. Lett. 79 (2001) 3618.
[2] H. Inokawa et al., International Electron Devices Meeting (IEDM) (2001) 147.

I (nA)

8

Vdd

stability points

7 a b
6

c

d

e

f

5

Io
MOS
FET

V

Vgg

I

Io

4
3

SET

2

output

2

3
4
V (V)

sampling pulses

input
f
e
d
c
b
a

5

Fig. 1. Two-terminal characteristics of the
SET-MOSFET negative-differentialresistance device operating at 27 K.
-13-

Fig. 2. Input-output waveforms of thequantizer.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Mechanism of Roughness Generation in Resists
Toru Yamaguchi and Hideo Namatsu
Device Physics Laboratory
Resist patterns less than 10 nm wide are indispensable for the fabrication of nanostructures, such as single-electron transistors. To form these patterns with high accuracy, wemust reduce the edge roughness of resist patterns. We have already clarified that theroughness is generated through a dissolution process, which we call aggregate extraction
development. Polymer aggregates 20-30 nm in size are naturally contained in resist films.
These aggregates are extracted one by one during development. They appear on the patternsurface, causing roughness. The aggregate extraction development was found to strongly
depend on the size of developer molecules. Thus, we can suppress it by using a developer
molecule of optimum size.
Figure 1 shows atomic force microscope (AFM) images of a resist surface during
development. Surface morphology differs largely with varying developer molecule size. For
hexyl acetate, which is usually used for high-resolution pattern formation, many aggregatesappear on surface [Fig. 1(c)]. For ethyl acetate, however, hardly any aggregates are observed[Fig. 1(a)].
In the dissolution of resist polymer, penetration of developer molecules into polymer
matrix is a limiting step. Developer molecules penetrate through voids, so-called free volume,
which are regions not occupied by polymer molecules. Therefore, the solubility of polymer
aggregates is determined by the relative relationship between the size of voids in aggregatesand molecular size of the developer. For a large developer molecule, such as hexyl acetate,polymers surrounding the aggregates dissolve first because the developer molecules easily
penetrate the surrounding polymers, but they have difficulty penetrating the aggregatesthemselves. This is due to the difference in void size between the surrounding polymers andaggregates. As a result, the aggregate extraction development occurs and the surface becomesrough. For a small developer molecule, such as ethyl acetate, on the other hand, theaggregates themselves dissolve because developer molecules can easily penetrate them. As aresult, the dissolution proceeds at the molecular level, not by aggregate extraction, and thesurface becomes flat. For butyl acetate, the situation is in between because its size is between
that of ethyl and hexyl acetate. These results indicate that there is an optimum developer
molecule size that will reduce resist roughness by suppressing aggregate extraction
development.
[1] T. Yamaguchi et al., Appl. Phys. Lett. 71 (1997) 2388.
[2] T. Yamaguchi et al., Proc. SPIE 3333 (1998) 830.

(a)

(b)

(c)

Fig. 1. AFM images of resist surface during development
Developer: (a) ethyl acetate, (b) butyl acetate, (c) hexyl acetate-14-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Carbon Nanotube Interconnection
Yoshihiro Kobayashi, Takayuki Yamashita, Yoshikazu Homma, and Toshio Ogino
Device Physics Laboratory
In the application of semiconductor nanostructures to electronic devices, interconnections
between individual nanostructures are very important for transmitting and processing signals.
However, with traditional wiring technology, it is quite difficult to fabricate the connections
between ultra-fine and dense nanostructures. To overcome this problem, we have proposed
wafer-scale nanointerconnection based on carbon nanotube (CNT) self-assembly [1,2].
CNTs are promising for wiring and connecting nano-scale devices because of their peculiar
mechanical and electrical properties. We have succeeded in fabricating a CNT network on anarray of nanometer-scale Si pillars.
Figure 1 shows statistical distribution of CNT growth behavior analyzed from samples
with Si pillar structure after CNT growth (see frontispiece). A CNT was grown by thermal
chemical vapor deposition (CVD) with an iron catalyst. The CNT was observed to grow on
3/4 of the Si pillars and about half of the grown CNT bridged the pillars in an orderly manner.
Such self-organized ordered bridging may be fairly anomalous since the CNT growth isordinarily postulated to be random in the thermal CVD process. We have proposed a bridging
growth mechanism where CNTs vibrate within a limited direction around a pillar and“search” for a neighboring pillar to stick to. The structure of the CNT was characterized by
micro-Raman spectroscopy in order to confirm this mechanism. Figure 2 compares theRaman spectra from a pillar-fabricated region and a flat region containing no pillars. The
Raman bands at 1316 cm-1 originate from the lowering of the translational symmetry due todefects. The spectra show that the bridging CNTs are more defective than those on the flat
region, although the bridging CNTs are observed to grow in linear manner and are supposed
to be less defective. This suggests that defects are formed by the vibration of CNTs during
bridging growth, which agrees with our growth mechanism.
[1] Y. Homma et al., Jpn. J. Appl. Phys. 41(2002) L89.
[2] Y. Homma et al., Physica B in press.
No Growth

Total:2004

76
CNT Growth55
45
Bridging

85
Fig. 1. The probability of CNT bridging
growth between Si pillars with a 100-nm
diameter and 300-nm height.

Fig. 2. The micro-Raman spectra observed
from a pillar-fabricated region and a flat
region containing no pillars.

-15-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Nanoparticles for Multi-Functionalization of Silicon:
A Plug and Play Approach
K. Prabhakaran and T. Ogino
Device Physics Laboratory

15
10 K
50 K
100 K
200 K
300 K

5.0

PL intensity

Magnetic Moment (emu)x10-6

Fabrication of nanostructures and their functionalization is essential to realize nanometre
sized devices. However, problems with the poor controllability of the size, shape, spatial
distribution and the functionality itself have been posing formidable challenges. This
underlines the need to develop alternative processes such as self-organization and othernature-driven processes. Here, we demonstrate a novel approach whereby, externallysynthesized nanoparticles are introduced on to the silicon wafer which is followed bymanipulation of surface chemical bonds to introduce a variety of functionalities. Since theparticles are synthesized externally this approach enables better control of various parameters.
Fe2O3 nanoparticles are introduced onto a device quality silicon wafer from a suspension inethanol through an ultrasonic bath. The samples are dried and loaded into an ultrahighvacuum chamber equipped with photoelectron spectrometer for monitoring the nature of thesurface species. On annealing the samples, the oxygen atoms change the bonding partnerfrom Fe to Si and desorbs as monoxide. This results in the complete reduction of the ironoxide particles to iron at around 760°C. These particles impart a soft-ferromagnetic property
to silicon as shown in figure 2. On depositing a thin layer of silicon onto this sample,
followed by annealing at 550°C, the sample exhibits light emission property. Figure 3 shows
the photoluminescence spectrum obtained from this sample. In summary, we could introduce
multiple functionality to silicon by treating it with nanoparticles, followed by manipulating
the surface chemical bonds.
[1] T. Ogino et al., Accoun. Chem. Res. 32 (1999) 447.
[2] K. Prabhakaran et al. Advanc. Mater. 13 (2001) 1859.

-5.0

He-Ne laser
Ge detector
12 K

1.61

1.65
1.57

-15

700 nm
Fig.1. AFM image of Si
sample treated with theparticles
followedbyannealing in UHV. Fe articles
of uniform size and shape areobserved.

-1000

0
Field (Oe)1000

Fig. 2. Magnetization datafrom the particle treated Si
showing hysterersis. Inset
shows the variation of
coercivity.

-16-

1.5
1.6
1.7
Wavelength (micron)Fig. 3. PL spectrum
recorded from theparticle treated Si
exhibiting
lightemission.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Overview of Material Science Research
Hideaki Takayanagi
Materials Science Laboratory
The Materials Science Laboratory (MSL) aims at producing new materials by controllingthe arrangement and coupling among atoms and molecules. By producing such materials,
MSL also aims to discover new quantum phenomena and to create new concepts. Toward
these goals, the following four MSL groups investigate a wide variety of materials, frominorganic matter, such as semiconductors, to organic matter, such as neurotransmitters. The
important feature of MSL is the effective sharing of nanofabrication and measurement
techniques developed originally in each group.
Molecular and Bio-Science Research Group
Creating new organic materials based on the manipulation of single molecules, andresearching information processing devices based on neural functions.
Superconducting Thin Films Research Group
Creating new high-Tc superconductors and applications to microwave communication using
the molecular beam epitaxy method.
Superconducting Quantum Physics Research Group
Creating a quantum computer using superconductor, and creating new magnetic devices
using quantum dot arrays.
Spintronics Research Group
Controlling the spin degree of freedom in a semiconductor and achieving new device
functions in future electronics.
The four major results obtained in fiscal year 2001 are as follows.
1. The neuronal responses in rat hippocampus induced by low magnesium content. Bymeasuring the spatial distribution of electrical activities using a special microelectrodearray, it is found that electrical bursts became highly active in a magnesium-free medium.
This indicates that magnesium ion could play a major role of neural activities in rat
hippocampus.
2. In-situ MgB2 thin film growth by the molecular beam epitaxy (MBE) method. MgB2 has
the highest superconducting transition temperature among non-oxide materials and is apromising for applications. The in-situ growth of MgB2 films without annealing atelevated temperatures is substantial progress toward the fabrication of Josephson
junctions.
3. A single shot readout of states in a flux quantum bit (qubit) with a superconductor ring.
This could be the basis for the creation of a quantum computer using superconductor. The
readout of the states is performed with sufficient accuracy by a DC-SQUID(superconductor quantum interferometer) aligned closely to the qubit.
4. A novel spin-filter device that has almost 100 % spin-filtering efficiency. The proposed
device consists of a triple-barrier structure made up of nonmagnetic semiconductors.
Electrons with a specific spin state are extracted by adjusting the emitter-collector bias
voltage.
The details of these accomplishments will be described in the following pages.

-17-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Neuronal Responses in Rat Hippocampus Induced by Low Magnesium
Keiichi Torimitsu, Nahoko Kasai, and Yasuhiko Jimbo
Materials Science Laboratory
Magnesium ion has been known to play an important role in biochemical processes anddevelopment. However, its role in neural processes is still unclear. In this research, we
focused on the effect of magnesium ion on the neural activities in rat hippocampal neurons.
The neuronal responses, such as electrical bursts and glutamate release were investigated in
rat hippocampus under low magnesium conditions. Measurements have been carried for
dissociated cell cultures and slice preparations. Electrical bursts were measured using a 64channel ITO microelectrode array. The size of the electrode was 10–50 µm each side. The
array was fabricated with lithographical techniques and directly connected to 64-channel
amplifier. Using this array, spatial distribution of the electrical activities could be measured.
Transient changes of glutamate release were measured using an enzyme-based
electrochemical detection method. The method includes glutamate oxidase, horseradish
peroxidase and mediator polymer. They were placed on each microelectrode. Hippocampal
neurons including slices were obtained from either P2 or P8 Wistar rat and cultivated them ona culture dish or a porous membrane for 7-14 days.
Electrical bursts turned to be highly active in a magnesium-free medium (MGF). A
transient increase induced by the MGF was detected in the glutamate concentrations in the
CA1, CA3 and dentate gyrus within a few minutes. Intracellular Ca concentration was also
increased transiently. The NMDA receptor antagonist, MK801 suppressed the increase onlyin the CA1, but not in the CA3 and dentate gyrus. The results may indicate the diversity of
NMDA receptor distribution and its dynamics in the hippocampus. Magnesium ion could be a
key in the control of the neural activities in rat hippocampus.
[1] N. Kasai et al., Neurosci. Lett. 304 (2001) 112.
[2] K. Torimitsu et al., Gordon Res. Conf. 3 (2002).

Fig. 1. Glu profiles at different positions and spike
numbers in a rat hippocampal slice-18-

Fig. 2. Glutamate release and Mg.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

In-situ Growth of Superconducting MgB2 Thin Films.
Kenji Ueda and Michio Naito
Materials Science Laboratory

Mg
B

Resisitivity (µ Ω cm)

The recent discovery of superconductivity at 39 K in MgB2 [1] has generated greatinterest in both basic science and practical applications. MgB2 has the highest
superconducting transition temperature (Tc) among non-oxide materials and its Tc is close tothat of La2-xBax(or Srx)CuO4, which were the first high- Tc superconductors. The Tc is slightly
higher than the theoretical upper limit predicted for phonon-mediated superconductivity,
which had been widely accepted until the discovery of superconducting cuprates. Therefore it
is important to clarify the superconducting pairing mechanism of MgB2, for which tunnelingspectroscopy on the clean surface of thin films of MgB2 should provide the most definite
evidence. With a view to superconducting electronics applications, the thin film form of
MgB2 is also required. MgB2 is a promising material for preparing Josephson junctions
because it has a simpler crystal structure, fewer material complexities, and a longer coherence
length (~ 5 nm) than cuprates in spite of its lower Tc. This scientific and practical interest
triggered intensive efforts to prepare high-quality thin films of MgB2.
The preparation of thin films of this rather simple intermetallic compound is impeded by
the large difference between the vapor pressures of Mg and B. Therefore, most initial efforts
employed the “two-step synthesis” in which amorphous B or Mg-B composite precursors areannealed at elevated temperatures with excess Mg in a sealed tube. However, this method is
unsuitable for the fabrication of Josephson junctions or multilayers [2]. We used a different
approach to avoid this problem and have recently succeeded in preparing the first ever asgrown MgB2 films by using molecular beam epitaxy [3]. This success was achieved by
reducing the growth temperature to as low as 300°C. The Tc is 35 K, which is close to the Tcof bulk MgB2. The in-situ growth of MgB2 films should enable substantial progress to bemade toward the fabrication of Josephson junctions.
[1] J. Nagamatsu et al., Nature 410 (2000) 63.
[2] K. Ueda, M. Naito, Studies of High Temperature Superconductors, in press.
[3] K. Ueda, M. Naito, Appl. Phys. Lett. 79 (2001) 2046.

150
100
50
0

0

50

100

150

200

250

300

Temperature (K)Fig. 2. Temperature dependence ofresistivity of MgB2 thin film.

Fig. 1. Crystal structures of MgB2.
-19-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Readout of Superconductor Quantum Bit
Hirotaka Tanaka, Siro Saito, *Masahito Ueda, and Hideaki Takayanagi
Material Science Laboratory*NTT Research Professor, Tokyo Institute of Technology
A quantum computer is expected to perform fast parallel computation. Realizing aquantum bit (qubit), which is a basic element of a quantum computer, requires the ultimate
controllability of the quantum system. We achieved a single shot readout of states in flux
qubit with superconductor ring. Thanks to recent developments in nanotechnology, we havecome close being able to control quantum states, which is a new paradigm of physics. The
flux qubit has two fundamental quantum states that have current circulating in clockwise andcounterclockwise directions. The readout of the states is performed by a DC-SQUID(superconductor quantum interferometer) aligned close to the qubit (see Fig.1). The DCSQUID can detect the magnetic flux generated by qubit circulating current. We
experimentally analyzed the readout characteristics of the flux qubit and found that our DCSQUID is capable of reading out the qubit state with sufficient accuracy (see Fig. 2).
The quantum state has so far been used to explain behavior of individual atoms, electrons andso on. But in superconductor ring, the quantum state is carried by more than a millions of
Cooper-pairs. Therefore, dynamics of this system are called macroscopic quantum
phenomena and are often discussed as regards the manifestation of Schrödinger’s cat. Thismeans that the mechanism of this system is of interest not only from computational viewpoint
but also from physical aspects.
[1] H. Tanaka et al., Physica C 368 (2002) 300.
[2] H. Tanaka et al., Supercond. Sci. Techonol. 14 (2001) 1161.
[3] H. Takayanagi et al., Proc. of Jubilee Nobel Symposium (Dec. 2001,Göteborg Sweden),to be published in Physica Scripta.

Fig.1. SEM (scanning electron
microscope) picture of the qubit and
DC-SQUID. The square inside is thequbit. The number of Josephson
junctions are two in the qubit and three
in the DC-SQUID. The Josephoson
junctions have 1-5 nm thick aluminumoxide.

Fig.2. The readout characterinstics of the
DC-SQUID. We clearly find the two linesthat correspond to different qubit states. Wechanged the external magnetic field, whichchanges qubit parameter. This readoutcharacteristics match the theoretical result.
(See also the color front page.)-20-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Proposal of a Spin-Filter Device using Nonmagnetic Semiconductors
Takaaki Koga and Junsaku Nitta
Materials Science Research Laboratory
Exploration of the spin degree of freedom in addition to the charge degree of freedom is
considered to be a key strategy for the realization of new device functions in the future
electronics. The research topics that have been pursued thus far from this point of view
include (i) the spin injection experiment from a ferromagnetic metal to a semiconductor, (ii)the electric control of the spin precession in a two-dimensional electron gas that is confined ina nonmagnetic semiconductor quantum well (QW), (iii) the magnetic control of electron spinsusing diluted magnetic semiconductors. Recently, we have proposed a novel spin-filter device
that combines the spin-orbit effect due to the built-in electric fields in the heterostructure anda triple barrier resonant tunnel diode [1]. This spin filter, which has almost 100 % spinfiltering efficiency, is unique in a sense that it does not use magnetic properties of materials.
This device, therefore, can be fabricated using nonmagnetic semiconductors only. Possible
applications of the device include the read-write devices for the information stored in spin
qubits or/and magnetic random access memories.
The proposed device consists of a triple barrier structure, where In0.53Ga0.47As andIn0.52Al0.48As are used for the QWs and the barrier layers, respectively (See Fig. 1). In
addition, the potential profile of the device has a particular mountain-like shape as shown in
Figs. 1(b)(c), which is a result of proper n doping in barriers 1 and 3 and p doping in barrier 2.
Because of this particular potential shape, the resonant tunneling levels that are formed in thefirst and second QWs (denoted as wells 1 and 2) experience spin splittings in a way theyreflect the positive and negative electric fields induced within wells 1 and 2, respectively. We
can, then, extract electrons with a specific spin state by adjusting the emitter-collector bias
voltage VEC properly. Shown in Fig. 2 are the calculated I-V curves of the proposed device forthree different device structures, using the transfer
matrix method. We see that the separation of the spinsplit I-V curve peaks is roughly proportional to themagnitude of the potential slope within the wells.
[1] T. Koga, J. Nitta, H. Takayanagi, and S. Datta,
Phys. Rev. Lett. 88 (2002) 126601.

Fig. 1. Schematic diagram of the proposed spin-filter
device.
-21-

Fig. 2. I-V characteristic of the
proposed device.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Overview of Quantum Physics and Electronics Research
Takaaki Mukai
Physical Science Laboratory
Our research in the fields of quantum physics and electronics, which is based on
semiconductor nano-structures fabricated by high-quality semiconductor crystal growth andadvanced device fabrication techniques, focuses on quantum electronic state control, carrierinteractions and wide-bandgap semiconductor physics. Our aim is the development ofinnovative semiconductor devices. Quantum Solid State Physics Research Group and WideBandgap Semiconductor Research Group are working in the following areas.
Quantum Solid State Physics Research Group(1) Carrier interactions in low-dimensional semiconductor heterostructures (carrier interactions 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) and nanoprobing (direct nano-scale imaging of electronic states by low-temperature STM).
Wide-Bandgap Semiconductor Research Group(1) High-quality GaN crystal growth by MOCVD and device processing technology.
(2) GaN semiconductor electronic/optical device physics (FET, HBT, LED and LD).
(3) Electron field emission in AlN cold cathode materials.
(4) High-quality diamond epitaxial growth and its characterization.
Major results obtained this fiscal year 2001 are reported in the following pages.
We have successfully measured the local density of states (LDOS) distribution bydifferential conductance measurement using scanning tunneling microscopy (STM) at low
temperature. It is confirmed that the measured LDOS distributions of a semiconductor
nanostructure coincides with the probability distributions of the zero-dimensional eigenstates.
This clearly demonstrates that we can now directly observe the nano-scale phenomena
predicted by quantum mechanics, as if we looked through a microscope.
Applying perpendicular magnetic field to two parallel layers of two-dimensional electron
gases separated by a thin tunnel barrier (electron bilayer system), two sets of Landau levels,
i.e., originating from the two subbands energetically separated by the tunneling gap, give rise
to many level crossings. We found there exists a finite energy gap even at the level crossing
point. This is a new class of integer quantum Hall effect which relies solely on interactions.
We fabricated light emitting diodes (LEDs) having AlGaN active layer whose possible
emission wavelength covers from 200 to 360 nm, and demonstrated high output power of 10
mW, i.e., one order of magnitude larger output than previous reports, at 352 nm wavelength.
Present external quantum efficiency is still low around 1 %, however, the internal quantum
efficiency has already been high enough as large as 80 %. This demonstrates that nitride
materials containing Al have strong potential for highly-efficient light emitting devices.
We fabricated Npn-type heterojunction bipolar transistor (HBT) applying our originallydeveloped p-InGaN layer with high hole concentration to a base layer. The measured
maximum current gain was as high as 20, which is a world-record for nitride-based HBT.
This demonstrates that the crystal quality of our p-InGaN layer is good enough and widebandgap nitride semiconductors show promise for high-power electronic devices.
-22-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Imaging of Zero-Dimensional States in a Semiconductor Nanostructure
Kiyoshi Kanisawa, Yasuhiro Tokura, Hiroshi Yamaguchi, and Yoshiro Hirayama
Physical Science Laboratory
The recent remarkable progress in fabrication process technologies has enabled thefabrication of nanometer-scale devices. Because electronic properties in the nanometer-scaleregion are governed by quantum mechanics, the development of quantum devices andquantum computers requires understanding and utilizing the wave phenomena of electrons in
nanostructures.
We have measured the local density of states (LDOS) distribution by differential
conductance (dI/dV) measurement using scanning tunneling microscopy (STM) at low
temperatures [1]. We imaged the electron wave characteristics of conduction electrons, aswell as the Friedel oscillation of two-dimensional electron gas (2DEG), at the semiconductor
surface of indium arsenide (InAs) thin film.
Using this technique, we imaged the LDOS of zero-dimensional (0D) electron waves
confined in a semiconductor nanostructure [2]. Figure 1 shows an STM image and schematic
illustration of a semiconductor nanostructure, a so-called stacking fault tetrahedron. We foundthat when the structure size is comparable to the electron wavelength, the nanostructure
behaves as a 0D structure (a quantum dot) and confines 2DEG in the accumulation layer at
the InAs surface. We also found that the LDOS distribution of a semiconductor nanostructure
coincides with the probability distribution of the 0D eigenstates. Such LDOS distributions areobserved at intervals of the 0D level separation. This is because electrons tend to exist at
discrete energy levels due to the quantization in the nanostructure. When the electron energy
coincides with the quantized levels, quantum mechanical resonance is observed as a higher
LDOS in the nanostructure than that in the surroundings.
[1] K. Kanisawa, M. J. Butcher, H. Yamaguchi, and Y. Hirayama, Phys. Rev. Lett. 86 (2001)
3384.
[2] K. Kanisawa, M. J. Butcher, Y. Tokura, H. Yamaguchi, and Y. Hirayama, Phys. Rev. Lett.
87 (2001) 196804.

Fig. 1. STM image and schematic illustration of nanostructure [left]; LDOS images(experiment) and 0D eigenstates (theory) [right]. Brighter region indicates higher LDOS.

-23-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Pseudospin Ferromagnetic Order in Bilayer Electron Systems
Koji Muraki, Tadashi Saku, and Yoshiro Hirayama
Physical Science Laboratory
With advanced semiconductor growth techniques, it is possible to prepare two layers of
two-dimensional electron gases separated by a thin tunnel barrier of a few nanometer thickness.
Such systems, referred to as bilayer electron systems, allow one to tune the strengths ofelectron-electron interactions and tunneling between two layers, and exhibit novel physicalproperties that can not be achieved in a single layer. In particular, perpendicular magnetic fields
enhance the electron-electron interactions by quenching the kinetic energy of electrons into
discrete Landau levels. In this study, we reveal that the electron system exhibits aferromagnetic order in particular situations when two Landau levels coincident at the Fermi
energy (EF) are regarded as up and down states of virtual spin (pseudospin).
We have fabricated a novel GaAs/AlGaAs quantum-well (QW) structure having both
front gate and n+-GaAs back gate to control the total electron density, ns, and the potential
symmetry independently [1, 2]. We employ a 40-nm wide single QW, which involves two
occupied subbands with symmetric (S) and antisymmetric (A) wave functions and therefore
behaves effectively like a bilayer [Fig. 1(a)]. When a perpendicular magnetic field, B, isapplied, two sets of Landau levels originate from the two subbands, giving rise to various
level crossings [Fig. 1(b)]. The energy diagram and the level crossings can be confirmed bymeasuring the magnetoresistance as a function of B and ns while keeping the QW potential
symmetric [Fig. 1(c)]. Activation measurements reveal that, at Landau level filling factor ν =3 and 4, there is a finite energy gap even when two levels cross at EF [Fig. 2(a),(b),(c)]. This
energy gap shows the existence of a ferromagnetic order in the electron system, which
suppresses the pseudospin flip and hence a dissipative current. This is a new class of integer
quantized Hall effect which relies solely on interactions.
[1] K. Muraki, N. Kumada, T. Saku, and Y. Hirayama, Jpn. J. Appl. Phys. 39 (2000) 2444.
[2] K. Muraki, T. Saku, and Y. Hirayama, Phys. Rev. Lett. 87 (2001) 196801.
a)b)(S, 1)(A, 0)

B

DSAS

A
S

c)
x1015

DN =3

(S, 0)

heB |g|mBB
m*
DN =1

DN =2

n=8

7

6

5

ns [m-2]

B [T]3(A, 0, ↓ )(A, 0, ↑ )Bn=3∆3 = 9.0 K∆4 = 5.8 K

B = 3.90 T

B = 3.31 T
E

1

2

1

1/T [K-1]
I

25

2
2

10

2

(S, 1, ↓ )(S, 1, ↑ )(S, 1, ↓ )(S, 1, ↑ )(A, 0, ↓ )(A, 0, ↑ )

B

c)

4

3

1

E
1

0

2.0

b) I n II= 4 III

10

10

3.5

0

ν=4

2

Rxx [Ω]|y i |

ν=3

E

4Activation Energy [K]

yi

a)

2

II

III

20

15

10

ν=4

5

ν=3

0

Fig. 1. (a) calculated wave functions for the
single QW. (b) Landau level energy diagram
in a bilayer system. (c) Gray-scale plot ofmagnetoresistance Rxx at 50 mK. Dark regions
represent small values of Rxx.
-24-

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Magnetic Field [T]Fig. 2. (a) Rxx vs 1/T. (b) energy
level diagram near the crossings forν = 3 and 4. (c) Activation energy as
a function of B.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Npn-type InGaN/GaN Nitride Heterojunction Bipolar Transistor (HBT)
Toshiki Makimoto, Kazuhide Kumakura, and Naoki Kobayashi
Physical Science Laboratory

n-GaN : Emitter
p-InGaN : Base
graded InGaN layer
n-GaN : Collector
n-GaN : subsub-collector
AlN buffer layer
SiC substrate
Fig. 1. Schematic structure ofan InGaN/GaN nitride HBT.

Collector C urrent (m A)

Wide-gap nitride semiconductors are promising materials for electronic devices that
require high power and/or operate under high temperatures. On the other hand, aheterojunction bipolar transistor (HBT), a kind of electronic devices, is suitable for highpower devices due to high breakdown voltages, high current densities, and good thresholdvoltage uniformity. Therefore, a nitride HBT is a promising electronic device in terms of bothmaterials and devices. However, there are few reports about nitride HBTs with high commonemitter current gains. In the previous reports, p-GaN was used for a base layer of a nitride
HBT and there are two major problems for the conventional p-GaN. One is its high resistivity
and the other is its severe damage induced by HBT fabrication process. To solve these two
problems, we have developed on p-InGaN layers and found that these p-InGaN layers showhigh hole concentrations above 1019 cm-3 at room temperature, meaning that their resistivity ismuch lower than that of the conventional p-GaN [1]. Furthermore, we have also found thatthese p-InGaN layers are less damaged by the process [2].
In this work, we have applied the low-resistivity and less-damaged p-InGaN layer to abase layer of a nitride HBT for the first time. Figure 1 shows an Npn-type InGaN/GaN nitride
HBT structure. For a collector layer, wide-bandgap GaN was used instead of InGaN to
increase a breakdown voltage. A graded InGaN layer was inserted between base and collector
layers to obtain higher current gains. Figure 2 shows the common-emitter current-voltage (IV) characteristics at room temperature. From these characteristics, the maximum current gain
was as high as 20, meaning that the crystal quality of this p-InGaN layer is relatively good
[3,4]. Furthermore, a high breakdown voltage over 20 V has been obtained due to widebandgap GaN collector. These device characteristics will be improved further by reducing
dislocation densities and process damage.
[1] K. Kumakura et al., Jpn. J. Appl. Phys. 39, (2000) L337.
[2] T. Makimoto et al., J. Cryst. Growth 221, (2000) 350.
[3] T. Makimoto et al., Appl. Phys. Lett. 79, (2001) 380.
[4] T. Makimoto et al., phys. stat. sol. (a) 188, (2001) 363.

10
β = 20

5

0
0

5

10

15

20

Collector-Em itter Voltage (V)Fig. 2. Common-emitter current-voltage (I-V)
characteristics at room temperature.
-25-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

AlGaN-based Light Emitting Diodes
Toshio Nishida and Naoki Kobayashi
Physical Science Research Laboratory
Aluminum gallium nitride (AlGaN) is a wide band-gap semiconductor having opticallydirect transition. Therefore, it will provide solid-state ultraviolet (UV) light sources in the
wavelength range of 200 – 360 nm. Such UV light sources have a wide variety of application
fields, including lighting, displays, spectrofluometry, photo-catalytic processes, and highresolution optics.
For efficient light emission or, in other words, radiative recombination, the introduction ofquantum well (QW) structure is desirable. We have, so far, clarified that suppressing theinternal polarization field in nitride heterostructures can enhance radiative recombination. To
improve the performance of UV light emitting diodes (LEDs) consisting of the AlGaN
material system, we introduced a short period alloy superlattice (SPASL) for the electricallyconductive and optically transparent cladding layers and for high-Al-content current blocking
layers to achieve effective current injection [1]. We also introduced high-quality GaN bulk
substrate to suppress non-radiative recombinations at crystal defects [2].
The structure of the UV-LED has 2-nm-thick AlGaN single quantum well (SQW) as anactive layer, which suppresses the internal polarization field. This active layer is sandwichedby n-type and p-type Al0.3Ga0.7N current blocking layers, and by n-type and p-type SPASL(Al0.16Ga0.84N / Al0.2Ga0.8N, 3nm period) cladding layers (Fig. 1). This device achieved amaximum output power of 10 mW at the emission wavelength of 352 nm (Fig. 2), which ishigher than the previous record in this UV wavelength range by one order of magnitude. The
highest external quantum efficiency is 1 %, and the estimated internal quantum efficiency is
as high as 80 % [2], which is comparable to that of conventional LEDs in the visible
wavelength range. Further, its emission spectrum is highly monochromatic without any
significant deep level emissions in the visible range.
We have also demonstrated the efficient application of this short wavelength UV-LED to
the excitation of fluorescence materials of the three basal colors (red, green, and blue) used inlighting and display devices [3].
[1] T. Nishida et al., Appl. Phys. Lett. 78 (2001) 3927.
[2] T. Nishida et al., Appl. Phys. Lett. 79 (2001) 711.
[3] T. Nishida et al., phys. stat. sol.(a) 188 (2001) 113.

Au
Pd/Au
p-blocking

p-SPASLAlGaN-SQW
n-blocking

n-SPASLn-GaN buffer
n-GaN sub.

Al/Au

30

20

10

0

AlN fraction (%)

Fig. 1. LED structure.

Fig. 2. Output power, efficiency, and the emission
spectrum of the AlGaN-based UV-LED.
-26-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Overview of Quantum Optics and Optical Materials Research
Takaaki Mukai
Physical Science Laboratory
In the fields of quantum optics and optical materials we pursue our studies for thedevelopment of core-technologies that will innovate optical communications and opticalsignal processing as well as for the scientific progress of the field. Optical State Control
Research Group, Ultrafast Optical Physics Research Group, Optical Device Physics ResearchGroup and Photonic Nanostructure Research Group are engaged in the subjects listed below.
Quantum 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) Coherent control of excitonic and spin states in quantum dots & wires.
(2) Optical properties in nitride-semiconductors and their device applications.
(3) Nano-scale fabrication process for photonic crystal materials.
Photonic Nanostructure Research Group(1) Two-dimensional photonic crystal optical circuits on SOI substrate (line/point defects).
(2) Three-dimensional photonic crystal structures and organic photonic crystal lasers.
(3) Interaction between photonic nanostructures and materials (negative refraction,
extremely-large group velocity dispersion).
Major results obtained this fiscal year 2001 are reported in the following pages.
We have proposed fault-tolerant simple quantum protocol for bit-commitment that isunbreakable by individual particle attacks. This is a successful example to extend the basic
idea of quantum cryptography, i.e., ultimate security guaranteed by uncertainty principle, toseveral magic protocols involving signature schemes, two-party secure computation, and soon.
We demonstrated a cross-correlation technique for measuring an ultrashort soft x-raypulse shape using the rapid increase in Kr+ ion density caused by optical-field induced
ionization. This technique can be a breakthrough to greatly improve the highest temporal
resolution of 1 ps realized so far by x-ray streak cameras.
Control of quantum mechanical superposition of an exciton in a single InGaAs quantum
dot (QD) was demonstrated by irradiating successive optical pulses with precise delay-phase
control. This demonstrates a phase rotation gate operation on the QD exciton as quantum bit
and reinforces the potential of QD excitons in quantum logic application.
We first fabricated efficient single-mode optical waveguides that operate within aphotonic bandgap wavelength, embedded in the two-dimensional photonic crystals on SOI
substrates. We have directly measured the dispersion of photonic crystal waveguides, andclarified that they have extremely large group dispersion. These results show promise forultra-small, highly- functional optical integrated circuits based on photonic crystal structures.
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Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Quantum Magic Protocols
Kaoru Shimizu and Nobuyuki Imoto*Physical Science Laboratory
Modern cryptography offers many functions such as authentication and signature schemes,
beyond usual uses for secret communication. Its security, however, relies on an unprovenassumption that solving some mathematical problems requires huge computational time
longer than the age of universe. By contrast, quantum cryptography aims at performing
security information processing through quantum-state manipulation of carrier particles suchas photon and guaranteeing the ultimate security on the basis of uncertainty principle ofquantum mechanics. The most successful example is quantum key distribution that makes it
possible for distant two parties to distribute a secure cipher key. It is, however, difficult toextend the basic idea of quantum cryptography to several magic protocols involving signatureschemes, two-party secure computation, and so on. Moreover, there have been clarified
fundamental difficulties in some of these efforts.
Our research motivations are to clarify (i) what kinds of quantum magic protocol are
possible in principle, and (ii) what kinds of advantage we can expect for magic protocols byuse of quantum mechanics. So far we have obtained two positive theoretical results on thesepoints. One is the proposal of quantum communication protocol for cipher-text transmissionthat allows repeated use of the same cipher key [1]. Another proposal is a fault-tolerant
simple quantum protocol for bit-commitment that is unbreakable by individual particle
attacks [2]. The former makes it possible for legitimate users to avoid security degradation in
the cipher key by monitoring the status of the key. The latter is a magic protocol for giving a
receiver any evidence of sender’s bit choice without revealing the bit value and is secureagainst any kinds of individual particle attack that is only a feasible attack until quantum
computer networks are developed. In comparison with conventional quantum bit commitment
protocols, our proposed scheme is mathematically far simpler, more efficient in terms oftransmitted photon number, and better tolerant of bit-flip errors. Figure 1 shows a four-path
single-photon interferometer that is employed as a quantum communication channel.
Quantum state of each propagating photon can be manipulated by controlling the interference
patterns [1].
* NTT Research Professor, Soken,The Graduate University for Advanced Studies.
[1] K. Shimizu and N. Imoto, Phys. Rev. A 60 (1999) 157, Phys. Rev. A 62 (2000) 054303.
[2] K. Shimizu and N. Imoto, Phys. Rev. A 65 (2002) 032324.
S'
P
Q

φ1
φ2

R
S

φ3
φ4

π /2
π /2

π/2
π/2

P'

MZI1
ϕ1
MZI2
ϕ2

S'

S'
MZI3
ϕ3
MZI4
ϕ4

d1 P
−π/2 d2 Q
d3 R−π/2 d4 S

P'P'
Bob's Decoder

Alice's Encoder

Fig. 1. Configuration of the four-path single-photon interferometer for the quantum channel.

-28-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Measuring an Ultrashort Soft X-Ray Pulse Shape
Katsuya Oguri, Hidetoshi Nakano, and Tadashi Nishikawa
Physical Science Laboratory
Recent developments in various ultrashort pulse x-ray sources based on a high-intensity
femtosecond laser have made experimental demonstrations of time-resolved x-ray absorption
and diffraction with picosecond to sub-picosecond resolution possible. The x-ray-pulse shapeis one of the most important parameters because its duration limits the temporal resolution ofthis time-resolved x-ray spectroscopy. To date, an x-ray streak camera has usually been used
for directly measuring x-ray pulses from nanosecond to picosecond, but its highest temporal
resolution is currently about 0.9 ps. Therefore, to measure a sub-picosecond x-ray pulse, it isessential to extend the kind of correlation techniques usually used for measuring afemtosecond laser pulse to the x-ray region.
We demonstrated a cross-correlation technique for measuring an ultrashort soft x-raypulse shape using the rapid increase in Kr+ ion density caused by optical-field induced
ionization, which operates as an ultrafast x-ray-absorption switch [1]. Using this technique,we measured a soft x-ray-pulse shape at 15.6 nm emitted from W plasma produced by a 100fs laser pulse. Figure 1 shows typical time-integrated spectra. A broadband soft x-ray
emission from W plasma is shown in Fig. 1 (a). In the transmission spectrum through Kr gas(Fig. 1 (b)), three absorption lines for neutral Kr atoms can be clearly observed near 13.5 nm.
When Kr gas was irradiated by the ionizing pulse 3 ps before the arrival of the soft x-ray
pulse, several Kr ion absorption lines appeared clearly while the absorption of neutral Kr
decreased considerably (Fig. 1 (c)). We plotted the differential transmittance at 15.6 nm,
which correspond to the absorption line of Kr+, as a function of the time delay between thelaser and soft x-ray pulses (Fig. 2). The differential transmittance is the convolution of thesoft x-ray pulse with the step-like change of the soft x-ray absorption. By fitting the
integrated Gaussian function to the data, we found the full width at half maximum of the soft
x-ray pulse to be 3.8 ps. This result agrees well with the duration measured with an x-ray
streak camera thus confirming the feasibility of this technique. The most notable feature ofthis technique is that we can expect the temporal resolution to become shorter than the laser
pulse duration, because the ionization is completed in the leading edge of the laser pulse.
[1] K. Oguri et al., Appl. Phys. Lett. 79 (2001) 4506.
Differential transmittanceIntensity [a.u.](a)(b) Kr

(c)

13.0

2+

Kr

14.0
15.0
Wavelength [nm]

+

Kr

0.3
0.2
0.1
0.0

-5

0

5

Time delay [ps]16.0

Fig. 1. Typical time-integrated spectra in
the 13 –16 nm wavelength range.
-29-

Fig. 2. Differential transmittance at 15.6
nm as a function of the time delay.

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Quantum Gate Operation of Quantum Dot Exciton Qubit
H. Kamada and H. Gotoh
Physical Science Laboratory

INTESITY (arb. unit)

Control of quantum mechanical superposition of an exciton in a single InxGa1-xAs
quantum dot was demonstrated. Coherent control of a quantum mechanical system is anultimate challenge, and it is essential toward realization of quantum computing. Rapidly
growing maturity of nanofabrication technologies have made quantum two-level system insolids promising for such approaches. Exciton confined within mesoscopic dot is such acandidate: The similarity between atoms and QD excitons together with the long-lived
coherence and the mesoscopically enhanced oscillator strength may offer a great opportunityof coherent manipulation of a well-defined single localized quantum system by optical field.
As an InxGa1-xAs quantum dot is exposed to electromagnetic radiation, the periodic
oscillation of electric field of the light is imprinted to exciton polarization. While thiscoherent dipole oscillation persists, the periodic energy exchange between the light and theexciton representing light absorption followed by coherent stimulated light emission, results
in a periodic exciton population oscillation: Or equivalently, the superposition of the exciton
existence oscillates. This is Rabi oscillation, which was confirmed previously. It is thenfeasible to generate any superposition of the exciton two-level wavefunction in an isolated
quantum dot with control of phase and strength of the light pulses. To demonstrate this, twolaser pulse excitation experiment with a precision delay control was undertaken. The first
pulse induced the exciton dipole oscillation and created a 30-40 % superposition state (Fig.1).
The second pulse delayed by 10 ps exactly in-phase with the first pulse added up the
population/superposition to a value twice as large as that created by first one. In contrast, as
the second pulse exactly out-of-phase to the first one erased the exciton population to null.
Such results are summarized in Fig. 1. Apparently, this demonstrates a phase rotation gate
operation on the quantum dot exciton as quantum bit and reinforces the potential of QD
excitons in quantum logic application.
[1] H. Kamada, H. Gotoh, J. Temmyo, T. Takagahara, and H. Ando, Phys. Rev. Lett. 87(2001) 246401.

1.668

out-of-phase

10 psin-phasesingle pulse

1.670

1.672

1.674

1.676

Fig. 1. Experimental demonstration ofcoherent control of exciton population byphase-locked optical pulse pair: The first
pulse creates an exciton superposition thatis either doubled or erased depending on
the relative phase.

1.678

PHOTON ENERGY (eV)-30-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Photonic-Crystal Single-Mode Waveguide
Masaya Notomi, Akihiko Shinya, and Itaru Yokohama
Physical Science Laboratory
Photonic crystal is an artificial dielectric structure of which refractive index is periodicallymodulated with the wavelength-scale dimension, which can be fabricated by the state-of-theart nano-fabrication technology. This crystal has a photonic band gap when a certain
condition is satisfied, and then it becomes an exotic photonic insulator which rejects the
propagation of light without any absorption. This unique feature is expected as a cutting-edge
break-through technology for realizing future photonic large-scale integrated circuits (LSI)
because we can confine the light in a ultrasmall volume by using this crystal.
With these motivations, we started the fabrication of Si-based photonic crystals with astrong collaboration with NTT Telecommunication Energy Laboratories by using e-beamlithography and dry etching, and have already reported a successful realization of twodimensional photonic crystals on SOI substrates having a wide photonic band gap between
1.3 to 1.6 µm covering today’s fiber communication wavelengths. Recently, we fabricatedefficient single-mode optical waveguides that operate within a photonic band gap wavelength.
In a photonic crystal having a gap, a line defect has a potential to serve as a tightly confined
single-mode optical waveguide, but practically this was not an easy task especially for SOItype photonic crystals. We have solved this problem by tuning geometrical structure of a line
defect in various ways, as shown in Fig. 1 [1]. In addition, we have directly measured
dispersion of photonic crystal waveguides for the first time, and clarified that they haveextremely large group dispersion, and the traveling speed of light can be largely reduced
down to 1/100 of the speed of light in air as shown in Fig. 2 [2]. This large reduction of
traveling speed is a direct manifestation of tunability of light propagation in photonic crystals
beyond the limitation of material itself. This tunability is especially important for high-speed
photonic information processing and also for enhancement of light-matter interaction.
[1] M. Notomi et al., Electron. Lett. 37, (2001) 243.
[2] M. Notomi et al., Phys. Rev. Lett. 87, (2001)
253902.

Fig. 1. SOI photonic-crystal single-mode
optical waveguide.

-31-

Fig. 2. Group dispersion of photoniccrystal waveguide (measurement).
Group index versus wavelength.

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

International Symposium on Mesoscopic Superconductivity andSpintronics
The international symposium named MS+S2002 was held on March 4-6, 2002, at the NTT
Atsugi R&D Center in collaboration with New Energy and Industrial Technology
Development Organization (NEDO) and the Physical Society of Japan (JPS). A field ofphysics called “Mesoscopic Superconductivity” includes Andreev reflection, asuperconductor/ferromagnet system, a π-junction, quantum coherence and a quantum bit.
Spintronics, that is made from spin and electronics, includes spin-related transport phenomena
and ferromagnetic semiconductors, etc. NTT Basic Research Laboratories has led both fields,
and the symposium aspired to gather the leading scientists and discuss the most recent topics.
Dr. Sunao Ishihara, Director of NTT Basic Research Laboratories, opened the symposiumwith welcoming remarks. Next, Dr. Hideaki Takayanagi, NTT R&D Fellow, Executive
Manager of NTT Basic Research Laboratories, gave a keynote address.
Oral sessions consisted of 51 presentations by invited speakers and contributed ones.
Poster sessions had 62 presentations. Prof. J. Clarke of University of California, Berkeley, theinventor of a superconducting interference device (SQUID), gave a plenary talk entitled “TheDC SQUID: From Traditional Designs to New Ideas for Quantum Measurement”. This wasfollowed by the observations of the quantum superposition and Rabi oscillations werediscussed in a SQUID as well as an ultrasmall superconducting dot. The time-domain
measurements of the Q-bit state were also reported by Chalmers University (Sweden) andYale University. We reported one-shot measurement of the Q-bit state by a dc-SQUID.
One of the main subjects in Spintronics was the spin-injection effect. Prof. E. Rashba ofMIT, who is famous for his pioneering work “Rashba effect”, discussed that spin injection
was the key to many new phenomena and applications in the field of the spin-polarized
electron transport. In the symposium we proposed a spin filter that utilized Rashba effect in aresonant tunneling structure.
The participants were 190 people [companies and universities: 149 (overseas: 64,
domestic: 126), NTT: 41]. Many participants were strongly impressed by the high quality ofthe presentations. The proceedings will be published in the special book by World Scientific.
The symposium was recorded on videotape and the tape has been used for public relations.

-32-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Award Winner’s List (Fiscal 2001)

The 4th Electronics
T. MukaiSociety Award
T. Saitoh(The Institute ofY. Yamamoto**NTT R&D Fellow
Electronics, Information
and Communication
Stanford Univ.
Engineers)“Pioneering Research on
Semiconductor Optical
Amplifiers”

Sept. 19,
2001

The EMS Award(20th Electronic
Materials Symposium)“MOVPE Growth and Large
Field Emission of Heavily
Si-doped Aluminum Nitrides

Jun. 22,
2001“Glutamate transients andneuronal bursts at multiple
positions in a rat cortex andhippocampus induced by low
magnesium”

Feb. 8,2002

SLOW-MAG AWARD(Gordon Research
Conference)

M. Kasu

K. Torimitsu
N. Kasai
Y. Jimbo
Y. Furukawa*
*

CREST

-33-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

In-house Award Winner’s List (Fiscal 2001)

NTT R&D Award

K. Kanisawa
H. Yamaguchi
Y. Hirayama
Y. Tokura"Direct Imaging of Electron Wave
Phenomena in a Semiconductor"

Dec. 2,
2001

Award forAchievements by
Director of Basic
Research
Laboratories

H. Namatsu“Advanced Nanolithography Using
Supercritical Fluid Technology”

Feb. 27,
2002

Award forAchievements by
Director of Basic
Research
Laboratories

M. Notomi
A. Shinya
I. Yokohama“Elucidation of Fundamental
Optical Properties in 2D Photonic
Crystals”

Feb. 27,
2002

Award forMeritorious Services
by Director of Basic
Research
Laboratories

T. Yamaguchi“Development of Chemical
Management System with
Barcode Readers”

Feb. 27,
2002

A. Fujiwara"Manipulation of Elementary
Charge in a Silicon
Charge-Coupled Device"
Nature vol. 410, 560-562 (2001)

Feb. 27,
2002

H. Kamada"Exciton Rabi Oscillation in aSingle Quantum Dot"
Phys. Rev. Lett. vol. 87, 246401(2001)

Feb. 27,
2002

Award for
Excellent Papers by
Director of Basic
Research
Laboratories
Award for
Excellent Papers by
Director of Basic
Research
Laboratories-34-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

List of Visitor’s Talks (Fiscal 2001)

l. Device Physics
Date

SpeakerJune

1 Prof. Christian Teichert

June

19 Dr. David Fraboulet& Dr. Barbara De Salvo

Sept. 14 Ms. Ruth Child

Sept. 14 Mr. Damiano Giubertoni

Oct.

17 Dr. Yuden Teraoka

Nov.

1 Dr. Robin Williams

Nov.

22 Ms. Berta Guzman

Nov.

28 Dr. Satyban Bhunia

Dec.

18 Dr. Takashi Sekiguchi

Affiliation"Topic"University of Leoben, Austria“Self-organization of nanostructures insemiconductor heteroepitaxy”
CEA-LETI, France“About CEA-LETI and research on silicon single
electronics in LETI”
University of Oxford, UK“Tunable mid-IR emission using a novel quantum
dot-quantum well coupled system”“STM study of germanium quantum dots on
patterned silicon surfaces as a function of growthtime”
The Center for Scientific and TechnologicalResearch (ITC-irst), Italy“Solid state reaction in Ti-Si bilayers: new resultsfrom in situ measurements”
Synchrotron Radiation Research Center,
Japan Atomic Energy Research Institute“Oxidation reaction dynamics of Si(001) surfaces
using supersonic O2 molecular beams”
Institute for Microstructural Sciences,
National Research Council, Canada“Ordered quantum dots for InAs/InP”
Universidad Politecnica de Madrid, Spain“Simulation of SiO2 build-up in silicon underoxygen bombardment”
The University of Electro-Communications“Fabrication of a GaInP/GaAs heterojunction
bipolar transistor (HBT) by MOCVD”“Real-time study of MOCVD growth process byusing synchrotron x-ray source”
Nanomaterials Laboratory, National Institute forMaterials Science“Cathodoluminescence and its application tovarious semiconductors”-35-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Dec.

18 Dr. Shigeo Tanuma

Dec.

20 Prof. Mitsuhiro Katayama

Feb.

22 Prof. Naoki Yamamoto

Feb.

22 Dr. V. Grillo

Feb.

27 Dr. Kazuhiko Hayashi

March 26 Prof. Yuji Takakuwa

Nanomaterials Laboratory, National Institute forMaterials Science“Calculation and measurements of electron
inelastic mean free paths in solids”
Osaka University“Atomic-hydrogen-induced self-organizationand hydrogen-surfactant effect on surfaces”
Tokyo Institute of Technology“Cathodoluminescence study of nano-structures insemiconductor epilayers”
Tokyo Institute of Technology“InAs/GaAs self assembled quantum dots study:
emission, strain and morphology by HRTEM and
CL-TEM”
Semiconductor Energy Laboratory Co., Ltd“Study on fabrication of nanometer-order structureson silicon surfaces and observation of their decay
processes using scanning tunneling microscopy”
Institute of Multidisciplinary Research for
Advanced Materials, Tohoku University“In-situ observation of the initial stage of the silicon
thermal oxidation by the real-time auger electron
spectroscopy combined with the reflection highenergy electron diffraction (RHEED-AES)”

ll. Materials Science
Date

SpeakerMay

8 Prof. Eiichi Nakamura

June

18 Dr. P. M. Koenraad

June

18 Dr. Ronald Cron

Aug. 17 Prof. Tomoji Kawai

Affiliation"Topic"The University of Tokyo“Highly effective chemical modification of fullerene– the course to metal-fullerene complex polymers”
Eindhoven University of Technology,
The Netherlands“Analysis of single and stacked InAs quantum dots
at the atomic level by cross-sectional STM”
CEA-Saclay, France“Electrical transport through one atom contacts”
Osaka University“Nanotechnology toward artificial bio-informationmaterials and devices”-36-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Oct.

2 Prof. Rudolf Gross

Dec.

14 Dr. Larry A. NagaharaJan.

10 Dr. Mutsuhiro ShimaJan.

25 Dr. Duanlian

March 15 Prof. Peter A. Gruenberg& Dr. D.E. Buergler

Technical University of Munich, Germany“Physics and applications of superconducting andmagnetic oxides”
Physical Sciences Research Laboratories,
Motorola Inc., USA“Molecular-scale engineering: what is needed
for success?”
Massachusetts Institute of Technology, USA“Nanostructured magnetic materials for data
storage applications”
Tokyo Medical and Dental University“Cisplatin augments TNF-a cytotoxity by inductionof apoptosis in glioblastoma cell lines”
Institute of Solid State Research (IFF),
The Research Centre Juelich, Germany“Structures of thin magnetic films separated bymetallic or semiconducting interlayers: growth,
structural, magnetic and magnetotransport
properties”

lll. Quantum Electron Physics
Date

SpeakerMay

15 Prof. Hiroyuki Sakaki

June

18 Prof. Yoshihisa Yamamoto

July

10 Prof. Michael B. Santos

Aug. 28 Dr. Jeremy O'Brien

Aug. 30 Dr. Adrian Avramescu

Affiliation"Topic"The University of Tokyo“Progress in telecommunication technology andnanostructure devices”
Stanford University, USA“Hardware technology for quantum information
processing”
University of Oklahoma, USA“Novel electronic properties of narrow-gap
quantum wells”
The University of New South Wales, Australia“STM fabrication of single phosphorus atom arrays
for a silicon quantum computer & an investigationof the 0.7 feature in GaAs open quantum dots”
The Institute of Physical and Chemical Research(RIKEN)“Growth of AlN-SiC solid solutions by sequential
supply epitaxy”-37-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Oct.

5 Dr. Huili Xing

Oct.

9 Dr. Rudolf Hey

Oct.

11 Prof. Klaus H. Ploog

Oct.

22 Prof. B. MonemarJan.

11 Prof. Yshai Avishai

March 6 Prof. Harry W. Tom

March 7 Dr. J. Herfort

University of California, Santa Barbara, USA“Progress in gallium nitride based bipolartransistors”
The Paul-Drude-Institute, Germany“Growth of a two-dimensional electron gas systemof high mobility and density”
The Paul-Drude-Institute, Germany“Tunneling-induced spin injection from Fe and
MnAs into GaAs”
Linkoping University, Sweden“Photoluminescence of excitons in
InxGa1-xN/InyGa1-yN multiple quantum wells”
Ben-Gurion University of the Negev, Israel“Electron tunneling through artificial and realmolecules”
University of California, Riverside, USA“Femtosecond laser-induced physical and chemical
processes at surfaces”
The Paul-Drude-Institute, Germany“Mound formation and its consequences for thegrowth of GaAs at low temperatures”

lV. Quantum Optics & Optical Materials
Date

SpeakerApril

5 Dr. Tetsuro Nikuni

June

25 Prof. Kazumi Wada

Sept.

5 Dr. G. Ravindra Kumar

Oct.

9 Prof. Wolfgang Husinsky

Oct.

12 Prof. A. A. Andreev

Affiliation"Topic"The University of Toronto, Canada“Dynamics of Bose-Einstein condensed gases atfinite temperature”
Massachusetts Institute of Technology, USA“Si Micro-photonics”
Tata Institute of Fundamental Research, India“Femtosecond, intense laser interaction with solids- hot electrons and megagauss magnetic fields”
Vienna University of Technology, Austria“The possible role of ballistic electrons inultra-fast laser ablation of metals: studied by
pump-probe experiments”
Research Institute for Laser Physics, Russia“Generation of superstrong laser fields and theirapplications”-38-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Jan.

22 Dr. Takashi Fujii

Jan.

23 Dr. Takeya Tsurumi

Jan.

30 Dr. Paulo V. Santos

Central Research Institute of Electric Power
Industry“Intense laser light propagation in the air using
mobile TW-laser system”
The University of Tokyo“A Bose-Einstein condensate trapped in a torus
potential”
The Paul-Drude-Institute, Germany“Dynamical modulation of quantum wells byhigh-frequency fields”-39-Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Research Papers Published in International Journals (Fiscal 2001)
The number of research papers published in the international journals (English) in fiscal
2001 amounted to 166 in Basic Research Laboratories as a whole. The number of papers
according to their research area is as follows.

Research Areas

Device Physics

Materials Science
Quantum Electron
Quantum Electron
Physics

Physics

Quantum Optics &Optical Materials
0

10

20

30

40

50

60

Number of Papers

The major journals and the number of published papers are shown below.
Specialized Journals
Name*（IF2000）

Number

Applied Physics Letters
Physical Review B(3.906)24(3.065)

12

Macromolecules(3.697)(1.157)(6.462)(2.198)(2.180)(1.375)(1.605)(0.592)(6.025)(2.831)(1.943)(9.000)(5.522)(3.695)(2.989)(2.091)

10
10
9
5
5
5
4
4
3
2
2
1
1
1
1
1

Japanese Journal of Applied Physics
Physical Review Letters
Surface Science
Journal of Applied Physics
Journal of Crystal Growth
Journal of Vacuum Science & Technology B
Material Science & Engineering B
Journal of American Chemical Society
Physical Review A
Journal of Physical Society of Japan
Reports on Progress in Physics
Advanced Materials
Chemical Communication
Optics Letters
Neuroscience Letters＊ IF2000: Impact factor 2000 Journal Citation Reports, 2000）

The average impact factor for individual research papers from all NTT Basic ResearchLaboratories is 2.37
-40-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

Presentations at International Conferences (Fiscal 2001)
The number of the presentations at the international conferences in fiscal 2001 amounted
to 253 in Basic Research Laboratories as a whole. The number of presentations according totheir research areas is as follows.

Research Areas

Device Physics

Materials Science
Quantum
QuantumElectron
ElectronPhysics
Physics
QuantumOptics
Optics&&Quantum
OpticalMaterials
Optical Materials
0

10

20

30

40

50

60

70

80

Number of Presentations

The major international conferences and the number of presentations are shown below.
Name
14th International Conference on the Electronic Properties of TwoDimensional System
13th International Conference on Crystal Growth/11th International
Conference on Vapor-Phase Epitaxy
Mesoscopic Superconductivity and Spintronics
2001 International Conference on Solid State Devices and Materials
28th International Symposium on Compound Semiconductors
2001 Materials Research Society Fall Meeting
4th International Conference on Nitride Semiconductors
14th Pacific Rim Conference on Lasers and Electro-Optics
10th Narrow Gap Semiconductor Structures
American Physical Society March Meeting
International Symposium on Superconducting Device Physics 2001
8th International Conference on Formation of Semiconductor Interface
14th Annual Meeting of IEEE Lasers and Electro-Optics Society
4th International Symposium on Blue Laser and Light Emitting Diodes
43rd Electric Material Conference
International Workshop of Photonic and Electromagnetic Crystal
Structures-41-

Number
16
13
11
10
9
7
6
6
5
4
4
4
3
3
3
3

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

List of Invited Talks at International Conferences (Fiscal 2001)

I. Device Physics(1) Y. Takahashi, “Silicon single-electron devices and their circuit applications”, The 1st
Annual US-Korea-Japan Workshop on Nanostructure Science/Technology, Seoul, Korea(April, 2001).
(2) H. Kageshima, K. Shiraishi, and M. Uematsu, “Theory of Si oxide growth rate taking
account of interfacial Si emission”, Electrochemical Society International Semiconductor
Technology Conference 2001, Shanghai, China (May, 2001).
(3) Y. Ono, K. Yamazaki, and Y. Takahashi, “Arithmetic operation by single-electrontransistors”, 2001 Silicon Nanoelectronics Workshop, Kyoto, Japan (June, 2001).
(4) M. Nagase, S. Horiguchi, A. Fujiwara, Y. Ono, K. Yamazaki, H. Namatsu, and Y.
Takahashi, “Single-electron devices formed by pattern-dependent oxidation”, 8thInternational Conference on Formation of Semiconductor Interface, Sapporo, Japan(June, 2001).
(5) H. Kageshima, M. Uematsu and K. Shiraishi, “Theory of Si thermal oxide growth ratetaking into account interfacial Si emission effects”, Bianual International Conference ofInsulating Films on Semiconductors, 2001, Udine, Italy (June, 2001).
(6) Y. Ono, Y. Takahashi, and H. Namatsu, “Single-electron and quantum SOI devices”,
Bianual International Conference of Insulating Films on Semiconductors, 2001, Udine,
Italy (June, 2001).
(7) Y. Homma and P. Finnie, “Step dynamics on growing silicon surfaces observed byultrahigh vacuum scanning electron microscopy”, The 13th International Conference on
Crystal Growth in Conjunction with The 11th International Conference on Vapor
Growth and Epitaxy, Kyoto, Japan (July, 2001).
(8) H. Kageshima, M. Uematsu, and K. Shiraishi, “Theory of Si oxide growth rate includinginterfacial Si emission effects”, 2nd Korea-Japan Workshop on Frontier Nanostructure,
Seoguipo, Korea (August, 2001).
(9) M. Nagase, S. Horiguchi, K. Shiraishi, A. Fujiwara, and Y. Takahashi, “Single-electron
devices formed by thermal oxidation”, International Symposium on Materials Processing
for Nanostructured Device, Kyoto, Japan (September, 2001).
(10) H. Inokawa, A. Fujiwara, and Y. Takahashi, “A multiple-valued single-electron SRAM
by PADOX process”, 2001 6th International Conference on Solid-state and Integrated
Circuit Technology, Beijing, China (October, 2001).
(11) A. Fujiwara, K. Yamazaki, and Y. Takahashi, “Si single-electron CCD”, International
Microprocesses and Nanotechnology Conference 2001, Matsue, Japan (October, 2001).
-42-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)(12) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi,
D. Bottomley, F. Lin, Z. H. Zhang, and A. Kaneko, “Atomic structure control on Si
surfaces and its application to nanofabrication”, International Workshop on
Atomic-Scale Surface Dynamics of Advanced Materials, Izunagaoka, Japan (November,2001).
(13) Y. Homma, A. Takano, and Y. Higashi, “Formation mechanism of oxygen-ion-induced
ripple topography”, 13th International Conference on Secondary Ion Mass Spectrometry
and Related Topics, Nara, Japan (November, 2001).
(14) Y. Takahashi, Y. Ono, A. Fujiwara, and H. Inokawa, “Silicon single-electron devices”,
7th International Symposium on Advanced Physical Fields, Tsukuba, Japan (November,2001).
(15) Y. Homma, P. Finnie, A. Kaneko, and T. Ogino, “Ultrahigh vacuum scanning electron
microscopy – toward the engineering of atomic steps –2”, 3rd International Symposium
on Atomic Level Characterization for New Materials and Devices, Nara, Japan(November, 2001).
(16) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi,
S. Suzuki, T. Yamashita, D. Bottomley, F. Lin, and A. Kaneko, “Design andfunctionalization of Si surfaces for self-assembled nano-architechture”, Yamada
Conference LVII, Atomic-Scale Surface Designing for Functional Low-Dimensional
Materials, Tsukuba, Japan (November, 2001).
(17) H. Namatsu, “Nanoline formation by using small aggregate resist and supercritical resist
drying”, 2001 Fall Meeting of Materials Research Society, Boston, USA (November,2001).
(18) Y. Takahashi, A. Fujiwara, Y. Ono, H. Inokawa, and K. Yamazaki, “Silicon
single-electron transistor and single-electron CCD”, 2001 Fall Meeting of Materials
Research Society, Boston, USA (November, 2001).
(19) S. Heun, L. Gregoratti, A. Barinov, B. Kaulich, M. Kiskinova, S. Suzuki, Y. Watanabe,
T. Ogino, W. Zhu, C. Bower, and O. Zhou, “Electronic structure of aligned carbon
nanotubes studied by photoemission microscopy”, IX ELETTRA Users Meeting, Trieste,
Italy (December, 2001).
(20) K. Prabhakaran, “Multifunctionalisation of silicon through nanoparticles: plug and play
approach”, International Symposium on Solid State and Materials Chemistry, Indian
Institute of Science (December, 2001).
(21) H. Omi, D. Bottomley, Y. Homma, T. Ogino, S. Stoyanov, and V. Tonchev, “Shape ofatomic steps on Si(111) under localized stress”, IV East West Surface Science Workshop,
Pamporovo, Blugaria (February, 2002).
(22) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi,
A. Kaneko, and F. Ling, “Atomic-structure and strain engineering for control ofself-organized Ge quantum nanostructures on Si surfaces”, Dr. Rohrer's JSPS Award
Workshop (International Workshop at IMR Tohoku University), Sendai, Japan (March,-43-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

2002).
(23) T. Ogino, “Control of single electron, control of single atom”, International
Nanotechnology Exhibition & Conference, Makuhari, Japan (March, 2002).
(24) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi,
S. Suzuki, T. Yamashita, F. Lin, and A. Kaneko, “Bottom-up approach for future Si
integration technology”, Flip Chip & Chip Scale Europa 2002, Bueblingen, Germany(March, 2002).
(25) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi,
S. Suzuki, T. Yamashita, F. Lin, and A. Kaneko, “Integration of semiconductor
nanostructures and interconnections for future self-assembled nano-architechture”,
Nanoarchitectonics Using Suprainteractions, Los Angels, USA (March, 2002).

II. Materials Science(1) M. Fujiki, “A question of parity conservation at the helical polysilylene level”, 2ndInternational Workshop Silicon Chemistry Polymers (ISPO2001), Canterbury, Kent, UK(June, 2001).
(2) Y. Jimbo, N. Kasai, and K. Torimitsu, “Multi-site recording of neuronal activity using
electrode array substrates”, International Workshop on Cell-Substrate Coupling,
Munchen, Germany (June, 2001).
(3) K. Furukawa and K. Ebata, “End-gated polysilane –synthesis, structure and properties ofsingle polysilane molecule tethered on solid surface”, International Workshop on Si
Containing Polymers, Canterbury (June, 2001).
(4) H. Shibata, “Optical study of the Josephson plasma in various high-Tc superconductors”,
Superconducting Device Physics 2001 (SDP2001), Tokyo, Japan (June, 2001).
(5) H. Takayanagi, “Reflectionless tunneling due to Andreev reflection in a gatedsuperconductor-semiconductor Junction”, Superconducting Device Physics 2001
(SDP2001), Tokyo, Japan (June, 2001).
(6) A. Matsuda, S. Sugita, and T. Watanabe, “Zn and Co impurity in Bi-2212 superconductor
probed by LT-STM”, International Workshop on Defects in Correlated Electron Systems,
Dresden, Germany (July, 2001).
(7) K. Torimitsu, Y. Furukawa, and H. Tabei, “Nanostructure controlled substrates:
nanostructure modification of bio-active substrates for nerve cell growth”, 8thInternational Conference of Composit Engineering, Tenereife, Spain (August, 2001).
(8) K. Torimitsu, Y. Furukawa, N. Kasai, and Y. Jimbo, “Sensapolooza: Guided tour of the
new silicon senses”, SIGGRAPH2001, Los Angels, USA (August, 2001).
(9) M. Naito, S. Karimoto, K. Ueda, and T. Greibe, “Epitaxy stabilized n-type-44-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

superconducting thin films”, The 2nd International Workshop on Novel Quantum
Phenomena in Transition Metal Oxides, Sendai, Japan (August, 2001).
(10) M. Naito and S. Karimoto, “High-quality large-area high-Tc films grown by molecularbeam epitaxy”, An International Conference on Advanced Ceramics and Glasses (PAC
RIM 4), Maui, USA (August, 2001).
(11) M. Fujiki, J. R. Koe, M. Motonaga, H. Nakashima, T. Sato, K. Terao, and A. Teramoto,“Switchable ambidextrous helical organopolysilylene”, 8th International Conference on
Circular Dichroism (CD2001), Sendai, Japan (September, 2001).
(12) M. Naito and H. Yamamoto, “Redox reaction at surface and interface of cuprates”,
Korean-Japanese International Workshop on Strongly Correlated Electron Systems,
Himeji, Japan (September, 2001).
(13) K. Torimitsu, “Molecular and Bioscience Research in NTT”, Tateshina Conference on
Organic Chemistry, Tateshina, Japan (November, 2001).
(14) M. Fujiki, “Switchable Hyper Helical Polymers toward Molecular Processors”,1st AIST
International Symposium on Nanotechnology, Tokyo, Japan (November, 2001).
(15) M. Naito, H. Sato, S. Karimoto, H. Yamamoto, and A. Tsukada, “Epitaxial
superconducting oxide films: strain enhanced pairing and epitaxy produced newmaterials”, Material Research Society (MRS) Fall Meeting, Boston, USA (November,2001).
(16) K. Torimitsu, N. Kasai, Y. Jimbo, and Y. Furukawa, “Glutamate transients and neuronalbursts at multiple positions in a rat cortex and hippocampus induced by low magnesium”,
Gordon Research Conference, Magnesium in biochemical processes and medicine,
Ventura, USA (February, 2002).
(17) Y. Jimbo, H. P. C. Robinson, and K. Torimitsu, “MEA-based neuronal recording”, WinterConference on Brain Research, Colorad, USA (February, 2002).

III. Quantum Electron Physics(1) N. Kobayashi, “Growth of GaN-based materials and their device applications”, 2001 The
Sino-Japanese Modern Engineering and Technology Symposium, Hsinchu, Taiwan (May,2001) .
(2) Y. Hirayama, “Spin related phenomena in semiconductor layer and dot structures”, CIAR(The Canadian Institute for Advanced Research) Nanoelectronics Program Meeting,Victoria, Canada (June, 2001).
(3) S. Tarucha, K. Ono, D. G. Austing, S. Sasaki, T. Fujisawa, Y. Tokura, and L. P.
Kouwwenhoven, “Tunable two-electron spin states in quantum dot structures andapplicability for making spin qubits”, The 59th Annual Device Research Conference(DRC), Notre Dame, USA (June, 2001).
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Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)(4) K. Kanisawa, M. J. Butcher, Y. Tokura, H. Yamaguchi, and Y. Hirayama, “Imaging ofwave phenomena at InAs(111)A surfaces using scanning tunneling microscopy”, FirstInternational Workshop on Quantum Nonplanar Nanostructures & Nanoelectronics ’01(QNN ’01), Tsukuba, Japan (July, 2001).
(5) K. Shiraishi, N. Oyama, K. Okajima, N. Miyagishima, H. Yamaguchi, K. Takeda, T. Ito,and T. Ohno, “First principle and macroscopic studies on semiconductor epitaxial
growth”, 13th International Conference on Crystal Growth (ICCG13), Kyoto, Japan (July,
2001).
(6) D. G. Austing and S. Tarucha, “Addition energy spectra of practical artificial atom andartificial molecule vertical quantum dot structures”, The Nano-Physics &Bio-Electronics Workshop, Dresden, Germany (August, 2001).
(7) T. Fujisawa, Y. Tokura, D. G. Austing, Y. Hirayama, and S. Tarucha, “Long-lived spinstate and spin blockade in a vertical quantum dot”, The 12th International Conference on
Nonequilibrium Carrier Dynamics in Semiconductors (HCIS-12), Santa Fe, USA(August, 2001).
(8) K. Kanisawa, M. J. Butcher, Y. Tokura, H. Yamaguchi, and Y. Hirayama,“Two-dimensional Friedel oscillations and electron confinement to nanostructures at a
semiconductor surface”, 2001 International Conference on Solid State Devices andMaterials (SSDM2001), Tokyo, Japan (September, 2001).
(9) H. Yamaguchi, R. Dreyfus, S. Miyashita, and Y. Hirayama, “Application of InAs
free-standing membranes for electromechanical systems”, 2001 International Conference
on Solid State Devices and Materials (SSDM2001), Tokyo, Japan (September, 2001).
(10) T. Matsuoka, “Substrates for epitaxial growth of InGaAlN system and growth on theirsubstrates”, Frontier Science Research Conference in Materials Science and Technology
Series ; Science and Technology of NITRIDE MATERIALS-2001, La Jolla, USA(November, 2001).
(11) T. Nishida and N. Kobayashi, “Highly efficient AlGaN-based UV-LED and its
application to visible light source”, SPIE Optoelectronics 2002, San Jose, USA (January,2002).
(12) T. Fujisawa, “Time-dependent phenomena of charge state and spin state in quantumdots”, International Workshop on Quantum Dots for Quantum Computing and ClassicalSize Effect Circuits (IWQDQC), Kochi, Japan (January, 2002).
(13) Y. Hirayama, K. Hashimoto, K. Muraki, and T. Saku, “Possible control of nuclear spinpolarization by two-dimensional electron gas”, 2002 RCIQE International Seminar on
Quantum Nanostructure and Their Device Applications, Sapporo, Japan (February,2002).
(14) T. Matsuoka, “Miscibility gap in wurtzite In1-X-YGaXAlYN“, Compound Semiconductor
Optoelectronic Materials and Device Workshop, Hsinchu, Taiwan (March, 2002).
(15) N. Kobayashi, T. Nishida, T. Akasaka, S. Ando, and H. Saito, “AlGaN UV-LEDs with-46-

Research Activities in NTT Basic Research Laboratories Vol. 12 (July, 2002)

high efficiency and InGaN LDs using grown facet mirrors”, 4th International
Symposium on Blue Laser and Light Emitting Diodes (ISBLLED-2002), Cordoba, Spain(March, 2002) .
(16) T. Fujisawa, “Time-dependent phenomena of a quantum dot in the coulomb blockade
regime”, The 10th JST International Symposium on Quantum Computing, Tokyo, Japan(March, 2002).
(17) T. Nishida and N. Kobayashi, “Fabrication of AlGaN-based ultraviolet light emitting
diodes”, International Symposium on Light of 21st Century, Tokyo, Japan (March,
2002).

IV. Quantum Optics & Optical Materials(1) M. Notomi, A. Shinya, E. Kuramochi, I. Yokohama, T. Tamamura, J. Takahashi, C.
Takahashi, T. Kawashima, and S. Kawakami, “Si-based photonic crystals as
guided-wave platforms: SOI slab and cross-dimensional structures”, International
Workshop of Photonic and Electromagnetic Crystal Structures (PECS III), St. Andrews,
UK (June, 2001).
(2) N. Uesugi, H. Nakano, T. Nishikawa, and K. Oguri, “Short X-ray pulse generation
towards time-resolved spectroscopy”, XVII International Conference on Coherent andNonlinear Optics (ICONO 2001), Minsk, Belarus (June-July, 2001).
(3) M. Notomi, A. Shinya, E. Kuramochi, I. Yokohama, T. Tamamura, J. Takahashi, C.
Takahashi, T. Kawashima, and S. Kawakami, “Si-based composite-dimensional photonic
crystals towards Si photonics”, The 4th Pacific Rim Conference on Lasers andElectro-Optics (CLEO/PR), Makuhari, Japan (July, 2001).
(4) H. Nakano, T. Nishikawa, K. Oguri, and N. Uesugi, “Time-resolved soft x-ray
absorption spectroscopy using femtosecond laser plasma x-rays”, International
Conference, Advanced Laser Technologies 2001 (ALT'01), Constanta, Romania(September, 2001).
(5) M. Notomi, A. Shinya, I. Yokohama, K. Yamada, J. Takahashi, and C. Takahashi, “2D
SOI photonic crystal slabs and line-defect waveguides”, The 14th Annual Meeting ofIEEE LEOS (LEOS 2001), San Diego, USA (November, 2001).
(6) M. Notomi, A. Shinya, K. Yamada, J. Takahashi, C. Takahashi, and I. Yokohama,“Si-based photonic crystals and photonic-band-gap waveguides”, SPIE Photonics West,
Optoelectronics 2002, San Jose, USA (January, 2002).
(7) H. Kamada, H. Gotoh, H. Ando, and T. Takagahara, “Coherent optical control of single
dot exciton wavefunction”, International Workshop on Quantum Dots for Quantum
Computing and Classical Size Effect Circuits (IWQDQC), Kochi, Japan (January, 2002).
(8) H. Kamada, H. Gotoh, H. Ando, and T. Takagahara, “Quantum gate operation ofquantum dot exciton”, The 10th JST International Symposium on Quantum Computing,Tokyo, Japan (March, 2002).
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Editorial Committee
Hiroyuki Kageshima
Toru Yamaguchi
Azusa Matsuda
Kaoru Shimizu

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