Research Activities
in
NTT Basic Research Laboratories
Volume 11
Fiscal 2000

August 2001
Nippon Telegraph and Telephone Corporation (NTT)Basic Research Laboratories

Atomic Force Microscopy Images

Semiconductor Surface with Strain Control
We have succeeded in obtaining a strain distribution controlled Si(001) substrate by forming
silicon oxide inclusions below the surface, for the first time. Strained epitaxial growth of Ge
on Si(001) produces three dimensional islands whose location and size distribution are
well-controlled. (Page.13)

SEM Viewgraph of Fabricated Line-DefectWaveguide Structure

Tranmission Spectra

Successful Fabrication of 2D Photonic Crystals
A photonic crystal is a periodical structure composed of different refractive-index materials andits use is expected to lead to the development of future ultra-small-sized optical integrated cirsuits.
Using SOI (Silicon On Insulator) structures, we have demonstrated 2D photonic crystal andline-defect structures with good transmission characteristics for the first time. (Page.19)

Topography

Local Density of States (LDOS)(Friedel Oscillation)

Friedel Oscillations in 2D Electron Gas Systems
at Semiconductor Surfaces
The feature of electrons as matter waves, one of the most significant conclusions fromquantum mechanics, should be taken into account and controlled to engineering the electrontransport in a nanoscale world. We have successfully imaged the electron waves (Friedel
Oscillations) by applying a scanning tunneling microscopy (STM) for epitaxially grownsemiconductor surfaces. Wavy LDOS patterns due to the electron wave interferences areclearly imaged in the vicinity of an isolated defect and inside of triangle nanostructures.
(Page.22)

Large Electron-Field Emission from Aluminum Nitrides
We have found large electron-field emission from heavily Si-doped AlN with negativeelectron affinity. In a basic display structure, we observed red, green, blue light emission from
phosphors excited by field-emitted electrons. Its luminance was intense enough for a practicaldisplay. (Page.23)

Preface
The mission of NTT Basic Research Laboratories is
to create, by exploring the frontier of technology andcreating a world-renown body of academic
knowledge, technology innovations that will comeinto play in perhaps 10 or 20 years. Hence, in linewith our enterprise strategy, we are developing newprinciples and concepts for the innovative technologies thatwill lead to NTT-group competitiveness and provide theinfrastructure of the IT society in the 21st century.
Nanotechnologies have attracted world attention oversince the U.S. government announced their significance inits national strategy. We have been systematic
studying nanoscience and nanotechnology for many
years. The social and industrial expectations to thenanoscience and nanotechnology are a good incentive
for us.
The fields of nanoscience and nanotechnology are further reflected in our researchplanning policy. We are aiming at breakthroughs that overcome the speed, capacity, powerconsumption, size, and security barriers to the future network. So, we are pushing research ofquantum information processing, ultimate electron devices, optical integrated circuits, andtrying to artificially create new materials. To carry out more effective research, we arecollaborating with outside parties based on our open-door policy, and actively harness outside
talent. In particular, we now have an Advisory Board that does peer reviews and evaluates ourlaboratories. The first Advisory Board meeting convened this past February. We are now
working to improve management based on the Advisory Board’s suggestions.
This booklet, “Research Activities in NTT Basic Research Laboratories,” is publishedannually to provide an overview of the research activities of the NTT Basic ResearchLaboratories. This volume reviews activities that have been conducted during fiscal year 2000. I
hope this booklet will lead to the exchange of scientific information and promote mutual
understanding among all scientists.
August 2001

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
E-mail: ishihara@will.brl.ntt.co.jp

Contents
page

Member List ･････････････････････････････････････････････････････････････ 1
Research Topics◆Overview of Device Physics Research ･･･････････････････････････････････････ 10♦Manipulation of Elementary Charge in a Silicon Charge-Coupled Device♦Sub-10-nm Electron Beam Lithography Using Inorganic Resist♦Semiconductor Surface with Strain Control♦Observation of Indium Phosphide Surface Structures in Metalorganic Vapor
Phase Epitaxy◆Overview of Materials Science Research ･････････････････････････････････････ 15♦Real-Time Monitoring of Neural Activity in the Brain♦Electron-Doped High-Tc Superconducting Thin Films Grown by Molecular
Beam Epitaxy♦Novel Material Design in Quantum Dot Superlattices♦Successsful Fabrication of 2D Photonic Crystals◆Overview of Quantum Electron Physics Research ･･････････････････････････････ 20♦Novel Kondo Effect in Quantum Dots
♦Friedel Oscillations in 2D Electron Gas Systems at Semiconductor Surfaces♦Large Electron Field Emission from Aluminum Nitrides◆Overview of Quantum Optics and Optical Materials Research ････････････････････ 24♦Optical Parametric Amplification in Fiber♦Efficient X-ray Generation from Femtosecond-Laser-Produced Plasma
on Nanostructure-Array Targets♦Exciton Rabi Oscillation in Single Quantum Dot

Data◆International Symposium on Carrier Interactions in Mesoscopic Systems ････････････ 28◆Advisory Board ･････････････････････････････････････････････････････････ 29◆Science Plaza 2001 ･･････････････････････････････････････････････････････ 30◆List of Award Winners････････････････････････････････････････････････････ 31◆List of In-House Award Winners････････････････････････････････････････････ 32◆List of Visitors’ Talks ････････････････････････････････････････････････････ 33◆Research Papers Published in International Journals ････････････････････････････ 38◆Presentations at International Conferences ････････････････････････････････････ 39◆List of Invited Talks at International Conferences ･･････････････････････････････ 40

Member List
As of March 31, 2001(*/ left NTT BRL in the middle of the year)

NTT Basic Research Laboratories
Director, Dr. Sunao Ishihara
Executive Research Scientist,

Dr. Katsumi Murase

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. 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. Kenji Shiraishi*
Nanostructure Technology Research Group:
Dr. Hideo Namatsu (Group Leader)
Torao Saitoh*
Dr. Masao Nagase
Toru Yamaguchi
Kenji Yamazaki
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. David Bottomley
Dr. Feng Lin‐2‐

Dr. Masashi Uematsu
Dr. Akira Fujiwara

Junzo Hayashi
Yoshio Watanabe

Dr. Yoshio Watanabe
Dr. Koji Sumitomo
Dr. Hiroo Omi
Dr. Paul Finnie*

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. Julian R. Koe*
Dr. Hongzhi Tang
Superconducting Thin Films Research Group:
Dr. Michio Naito (Group Leader)Dr. Hisashi Sato
Dr. Shin-ichi Karimoto
Dr. Kenji Ueda
Superconducting Quantum Physics Research Group:
Dr. Hideaki Takayanagi (Group Leader)
Dr. Azusa Matsuda
Dr. Junsaku Nitta
Dr. Tatsushi Akazaki
Dr. Hayato Nakano
Dr. Yuichi Harada
Dr. Takao Watanabe
Dr. Hiroyuki Tamura
Hirotaka Tanaka
Dr. Takashi Kimura
Dr. Takaaki Koga
Dr. Rais Shaikhaidarov*
Dr. Chinnathambi Sekar*
Nano-Structure Materials Research Group:
Dr. Itaru Yokohama (Group Leader)
Dr. Nobuhiko Susa
Dr. Jiro Temmyou
Dr. Masaya Notomi
Eiichi Kuramochi
Dr. Akihiko Shinya‐3‐

Dr. Yasuhiko Jimbo
Dr. Katsuhiro Ajito
Hiroshi Nakashima

Dr. Hideki Yamamoto

Kouichi Semba
Dr. Noriyuki Hatakenaka
Satoshi Sugita*
Dr. Yoshiaki Sekine
Dr. Shiro Saito
Dr. Kenichi Matsuda

Tetsuyoshi Ishii
Dr. Atsushi Yokoo

Physical Science Laboratory

Executive Manager,

Dr. Takaaki Mukai
Dr. Akihito Taguchi

Quantum Solid State Physics Research Group:
Dr. Yoshiro Hirayama (Group Leader)
Dr. Kotaro Tsubaki
Dr. Yasuhiro Tokura
Tadashi Saku
Dr. Toshimasa Fujisawa
Dr. David Guy Austing
Dr. Kiyoshi Kanisawa
Kyoichi Suzuki
Dr. Toshiaki Hayashi
Wide-Bandgap Semiconductor Research Group:
Dr. Naoki Kobayashi (Group Leader)
Dr. Toshiki Makimoto
Dr. Makoto Kasu
Dr. Seigo AndoDr. Yasuyuki Kobayashi
Dr. Toshio NishidaDr. Narihiko Maeda
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Quantum Optical State Control Research Group:
Dr. Takaaki Mukai (Group Leader)
Dr. Kyou Inoue
Dr. Kaoru Shimizu
Dr. Tetsuya Mukai
Dr. Fumiaki Morikoshi

Dr. Hiroshi Yamaguchi
Dr. Koji Muraki
Dr. Satoshi Sasaki

Dr. Takashi Matsuoka
Hisao Saito
Yoshiharu Yamauchi
Masanobu Hiroki

Dr. Makoto Yamashita

Ultrafast Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Mahesh R. Junnakar*
Dr. Tadashi Nishikawa
Katsuya Oguri
Dr. Tsuneyuki Ozaki

Dr. Ryuzi Yano
Dr. Jingquan Lin

Optical Device Physics Research Group:
Dr. Tadashi Saito (Group Leader)
Hidehiko Kamada
Masami Kumagai
Dr. Arturo Chavez-Pirson*
Dr. Hideki Gotoh

Dr. Shunji Nojima
Dr. Hailong Wang

‐4‐

Distinguished Technical Members

Yoshiro Hirayama was born in Kanagawa on July 18, 1955. He received the B.E., M.S. and
Ph.D. degrees in electrical engineering from the University of Tokyo in 1978, 1980 and 1983,
respectively. He joined NTT Basic Research Laboratories in 1983. He was a guest scientist in
Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany during 1990-1991. Since
1983 he has engaged in the study of semiconductor fine structures fabricated byfocused-ion-beam technique, transport characteristics of semiconductor mesoscopic systems
and ballistic transport in high-mobility semiconductors. His current interests are transport
properties of semiconductor layer and nano structures including carrier interaction phenomena.
He is a research coordinator of NEDO international joint research project (NTDP-98) since1998, and also a coordinator of CREST research team for interacting carrier electronics since1999. He is an associate editor of Japanese Journal of Applied Physics, and a member of theJapan Society of Applied Physics, the Physical Society of Japan and IEEE.

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.
‐5‐Advisory Board (2000 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

Professor
Paul-Drude-Institut für Festkörperelektronik
Germany

Dr. Michel H. Devoret

Director of Research
Quantronics Group
SPEC, CEA-Saclay, France

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‐6‐

Invited Scientists (2000 Fiscal Year)

Name

Affiliation
PeriodProf. Klaus-J. Friedland

Paul-Drude-Institut für Festkörperelektronik, Germany
March – April, 2000

Prof. Anatoly F. Volkov

Institute of Radioengineering and Electronics of the Russian
Academy of Sciences, Russia
March – April, 2000

Prof. Zhaohui Zhang

Peking University, P.R. China
April, 2000 – February, 2001

Prof. Michael B. Santos

University of Oklahoma, USA
August – December, 2000

Prof. Joseph Imry

Weizman Institute of Science, Israel
August – September, 2000

Prof. Yshai Avishai

Ben-Gurion University, Israel
September – October, 2000

Prof. Thomas Schäpers

Institut für Shinchten und Grenzflächen
Forschungszentrum Jülich, German
October, 2000 – February, 2001

Prof. Alexander Khaetskii

Institute of Microelectronics Technology of the USSR
Academy of Sciences, Russia
September – November, 2000

Prof. Stoyan Stoyanov

Institute of Physical Chemistry, Bulgarian Academy of
Science, Bulgaria
November, 2000 – January, 2001

‐7‐

Trainees(2000 Fiscal Year)

Name

Affiliation (Period)

Matthew Butcher

University of Nottingham, UK (Feb. 00 – May 00）

Sabrina Kohler

Institut National Des Sciences Appliquées, France(Mar. 00 – Aug. 00)

Wilfred van der Wiel

Delft University of Technology, The Netherlands(May 00 – Aug. 00)

Barbara ResselCharles University, Italy (May 00 – June 00)

Enjalbert Fabrice

Ecole Nationale Supérieure de Physique de Grenoble(ENSPG), France (June 00 – Sep. 00)

Federico Rosei

University of Rome, Italy (July 00 – Sep. 00)

Marlies Comelia Goorden

Delft University of Technology, The Netherlands(Aug. 00 – Nov. 00)

Remi Dreyfus

Ecole Supérieure de Physique et de Chimie Industrielles dela ville de Paris (ESPCI), France (July 00 – Dec. 00)

Claire Akiko Kikuchi

Ecole Supérieure de Physique et de Chimie Industrielles dela ville de Paris (ESPCI), France (Aug. 00 – Dec. 00)

Tine Greibe

Technical University of Denmark, Denmark(Sep. 00 – Mar. 01)

Soren Jensen

Technical University of Denmark, Denmark(Sep. 00 – Mar. 01)

Hubert Heesche

Delft University of Technology, The Netherlands(Sep. 00 – Jan. 01)

Antoine Brehier

University of Paris-Orsay, France(Sep. 00 – Dec. 00)

Jeroen Elzerman

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

Wilfred van der Wiel

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

Ronald Hanson

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

Jean Delmas

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

Elise Laffosse

Institut National Des Sciences Appliquées, France(Mar. 01 – Aug. 01)‐8‐

Japanese Students(2000 Fiscal Year)

Name

Affiliation (Period)

Kazuya Aoki

Science University of Tokyo, Japan (Apr. 00 – Mar. 01)

Tetsuya Asayama

Tokyo University, Japan (Apr. 00 – Mar. 01)

Yusuke Asari

Waseda University, Japan (July 00 – Mar. 01)

Shinichi Amaha

Tokyo University, Japan (Apr. 00 – Mar. 01)

Taizo Ichikawa

Shonan Institute of Technology, Japan (May 00 – Mar. 01)

Tatsuro Kawabata

Tokai University, Japan (Apr. 00 – Mar. 01)

Atsushi Kawaharazuka

Waseda University, Japan (Apr. 00 – Mar. 01)

Yoshitaka Kitamura

Tokyo University, Japan (Apr. 00 – Mar. 01)

Tomoaki Kimura

Shonan Institute of Technology, Japan (Dec. 00 – Feb. 01)

Hiroyuki Sasabu

Seikei University, Japan (Apr. 00 – Mar. 01)

Yuki Sato

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

Akio Tsukada

Science University of Tokyo, Japan (Apr. 00 – Mar. 01)

Asuka Terai

Tokai University, Japan (Apr. 00 – Mar. 01)

Yoshimichi Nakamura

Waseda University, Japan (Apr. 00 – Mar. 01)

Yoshifumi Nishi

Tokyo University, Japan (Apr. 00 – Mar. 01)

Emi Hagiwara

Tokai University, Japan (Apr. 00 – Mar. 01)

Takanori Hayashi

Science University of Tokyo, Japan (Apr. 00 – Mar. 01)

Noriko Fukai

Shonan Institute of Technology, Japan (May 00 – Mar. 01)

Takenori Fujii

Science University of Tokyo, Japan (Apr. 00 – Mar. 01)

Motonari Honda

Tokyo University, Japan (Apr. 00 – Mar. 01)

Takayuki Yamashita

Tokai University, Japan (Apr. 00 – Mar. 01)

Michihisa Yamamoto

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

Masahiro Wada

Waseda University, Japan (Apr. 00 – Mar. 01)‐9‐

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Overview of Device Physics Research
Toshio Ogino
Device Physics Laboratory
Evolution of information technology is based on semiconductor devices of ultrahighspeed, low power dissipation, and ultrahigh density. The ultimate goal of silicon integrated
system will be the control of a single electron in device functioning and control of a single
atom in the fabrication process. Towards single electron control, we are proceeding withresearch on single electron transistors, single hole transfer devices, nanofabrication processes
required for production of nano-scaled devices, and modeling of the Si oxidation process.
Towards single atom control, we are developing a new approach of wafer-scale integration ofself-organized nanostructures based on surface structure control. As a common basis for thesegoals, we are investigating new techniques for characterization of materials and device
structures.
The single electron transistor is a device whose power dissipation is expected to be theminimum possible. We have already succeeded in fabricating an inverter that is a basic logic
circuit element. In 2000, we fabricated an adder using our single electron transistors anddemonstrated its operation. In addition to single electron circuits, we invented a single holetransfer device that is completely unprecedented. In this device, electrons and holes are
spatially separated and the transport of a single hole is detected by the electron current. The
single electron transistor was also applied to a new multiple-valued memory. We proceededwith characterization of the inside structure of the single electron transistor using scanningelectron microscopy and considered theoretically the mechanism of single electron operation.
The most important process in Si technology is thermal oxidation of Si. We have shownthat oxidation behavior under various oxidation conditions can be interpreted by the universal
model for thermal oxidation which was proposed by this laboratory.
Towards room temperature operation of single electron devices, we are developing
nanofabrication processes including electron beam lithography and resist processes. In
nano-scale devices, pattern formation without roughness is indispensable. We have clarified
the roughness generation mechanism and developed a new resist which can form a patternwith a very small roughness.
Conventional semiconductor devices are fabricated using resist patterns that aretransferred from masks. On the other hand the "bottom-up process", in which device
structures are fabricated from atomic structures on the substrate surface, attracts muchattention. Towards realization of this process, we are investigating wafer-scale control of
atomic structures on silicon surfaces. The dynamics of atomic steps and reconstructeddomains were analyzed using scanning electron microscopy and low-energy electron
microscopy. In order to control the arrangement of self-organized nanostructures, we havedeveloped a novel technique to control the strain distribution on silicon surfaces: oxide
inclusions are used to generate strain. We investigated the growth mechanism of Ge
nanowires on Si surfaces. A new technique to form functional nanoparticles on Si surfaces
has been proposed. By way of new materials research, we have started research on the growthand characterization of carbon nanotubes. We have established a novel characterization
technique to observe the atomic structure of semiconductor surfaces during vapor-phasegrowth. This technique was applied to the analysis of the reconstruction of InP surfaces in ahydrogen ambient.

‐10‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Manipulation of Elementary Charge in a Silicon Charge-Coupled Device
Akira Fujiwara and Yasuo Takahashi
Device Physics Laboratory
Single-electron (SE) devices have been attracting much attention in light of theunderlying physics and the application to future integrated circuits. Though the manipulationof single electrons becomes possible in the so-called SE pump consisting of coupled
conductive islands, the fabrication is no easy because it needs the integration of multiple
tunnel capacitors. The SE manipulation has not yet been performed in Si devices. Recently wehave developed a novel-type SE device oriented for large-scale integration [1]; it is the SE
charge-coupled device (CCD), in which a single hole was stored and transferred at 25K. For
sensing the hole, we demonstrate a new scheme based on the electron-hole system in Si
nanostructures.
Figure 1(a) shows a top-view SEM image of the device. It is a closely packed array of two
Si-wire MOSFETs with fine poly-Si gates. The Si wire is T-shaped so that each end isconnected to three n-type electrodes, enabling us to detect the electron currents through each
MOSFET separately. Figure 1(b) and (c) describe how the single hole is stored andtransferred between the two Si channels, and is sensed by the electron currents. The hole isgenerated by illumination. Its storage and transfer are done simply by applying the negative
voltages to the poly-Si gates and controlling them like the CCD. For the sensing, the hole andthe electrons are kept apart by the large electric field across the Si wire, and therefore do notrecombine soon. Since the wire diameter is as small as 15-20 nm, the electron current ishighly sensitive to the number of holes (nh), thus realizing the elementary-charge sensitivity.
The results for the single-hole manipulation are shown in Fig. 2. The sensing and thetransfer of the single hole were repeated a few times. The sensing currents alternately have ahigh level. This means that the single hole was successfully transferred back and forth
between the two Si-wire MOSFETs.
[1] A. Fujiwara and Y. Takahashi, Nature 410 (2001) 560.

Fig. 1. (a) Top-view SEM image of the device.
(b) Transfer and sensing of the single hole.
(c) Cross-sections of the Si wire.
‐11‐

Fig. 2. Manipulation of a single holebetween the two MOSFETs.

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Sub-10-nm Electron Beam Lithography Using Inorganic Resist
Kenji Yamazaki, M. S. M. Saifullah*, Toru Yamaguchi, and Hideo Namatsu
Device Physics Laboratory
In order to make high performance nanodevices like single-electron devices working atroom temperature, nanofabrication at the scale of sub-10 nm is necessary. To enable that,electron beam (EB) nanolithography on inorganic resists has been tried by many groups. The
sensitivity of conventional inorganic resists, however, is too low for these resist to be applied
to make high-performance nanodevices.
We have developed a new organic/inorganic composite resist that has much higher
sensitivity than conventional inorganic resists and sufficient resolution for our purpose. This
resist is a chelete compound of a metal alchoxide chemically modified by a !-diketone [1].
EB exposure causes separation of the diketone from the compound, which is followed byspontaneous crosslinkage of the alchoxide. Thus, it can be used as a negative-tone resist to an
EB. As the primary reaction due to the EB occurs at the organic ketone part, not at inorganicparts, this resist is more than a hundred times more sensitive to the EB, compared toconventional inorganic resists. The resist enables finer patterning and provides smallline-edge roughness due to its structure being as small as a few nanometers.
We have evaluated this resist using our EB nanolithography system at 100-kV
acceleration voltage. Besides its small beam size, this system has high stability andreproducibility for sub-10-nm scale lithography. For example, the beam positioning error isless than 2 nm for 10 minutes, and the reproducibility of the stage position is as good as 1-2
nm after 500 stage movements [2].
Figure 1 shows fine lines of the resist exposed to the EB using the system. The width ofthe lines formed at the center of the main deflection field is about 8 nm. We could also obtainfine lines as narrow as about 10 nm on the boundary of a 320-"m-square mainfield. Good
reproducibility and low fluctuation of linewidth are obtained, and the linewidths at the centerand the boundary of the field correspond to the diameters of the EB simulated there. These
results mean the resist pattern strictly reflects the distribution of the energy absorbed in resist.
[1] M. S. M. Saifullah et al., Jpn. J. Appl. Phys. 38 (1999) 7052.
[2] K. Yamazaki et al., Proc. SPIE. 3997 (2000) 458.
* present address: Engineering Faculty, Cambridge Univ., U.K.

Fig. 1. 8-nm-wide lines of composite resist formed at the center of the mainfield. Lines werereproducibly formed with small line edge roughness along both x- and y- axis.
‐12‐Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Semiconductor Surface with Strain Control
Hiroo Omi, David Bottomley, and Toshio Ogino
Device Physics Laboratory
Looking to the long term future of Si semiconductor technology, we have proposed,
fabricated and demonstrated strain distribution control on the planar Si wafer scale foradvanced nanostructure self-assembly. Self-assembled growth attracts much attention because
it is free from the optical lithography minimum feature size limit. In most research to date on
nanostructure formation on Si surfaces, the substrate was not subjected to advanced
preparation procedures. Preparation typically consisted of chemical etching followed bythermal treatment in ultra high vacuum. The size variation of Ge or GexSi1-x alloy
nanostructures grown coherently on the surface was appreciable, with no localization control.
As a result the structures are difficult to utilize effectively in commercial applications.
Here we apply commercially-viable industrially-proven processes to prepare the Si wafer
for advanced nanostructure fabrication. Pre-deposited layers on the surface of the wafer are
patterned using optical lithography; oxygen ions are implanted; the sample is subjected to a
1325!C anneal, and finally the pattern is removed in a chemical etch. The oxide inclusions arecompletely stable up to at least 1325!C and are therefore compatible with further fabrication
processes. The O ion implantation and annealing approach is a spinoff from the silicon on
insulator (SOI) field, specifically the separation by implanted oxygen (SIMOX) process
invented 23 years ago at NTT.
Strained epitaxial growth of Ge on the Si(001) substrate surface at 550!C in ultra highvacuum produces three dimensional islands whose location and size distribution are
well-controlled (Fig. 1). Ge grows forming three dimensional islands surrounded by a wetting
layer. The growth mode occurs to reduce the combined surface energy and elastic energy ofthe system. Growth on a line pattern produces aligned, closely-spaced islands with a highly
uniform size distribution (Fig. 1(a)). In Fig. 1(b), the islands have self-organized into a ring at
the centre of the implanted region.

Fig. 1. Atomic force microscopy images of the surface after growth of Ge (a) on a 700 nm
implantation width line pattern (b) on a 2 "m implantation diameter hole pattern．
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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Observation of Indium Phosphide Surface Structures in Metalorganic
Vapor Phase Epitaxy
Tomoaki Kawamura and Yoshio Watanabe
Device Physics Laboratory
Understanding surface structures is one of the fundamental issues in epitaxial growth.
Reflection high energy electron diffraction is routinely used in molecular beam epitaxy(MBE). In metalorganic vapor phase epitaxy (MOVPE), optical tools, such as reflectancedifference spectroscopy (RDS) and surface photoabsorption (SPA), are used. However,surface structures in MOVPE growth are still uncertain because of the low spatial resolution
owing to the longer wavelength of visible light.
A crystallographic structure analysis by using x-ray diffraction is known as a powerfultool for determining the atomic arrangement in bulk crystals, and has also been applied inanalyses of surface structures in liquid and gaseous environments. Additionally, owing to
the low interference between x-rays and materials, a quantitative treatment of measurement ispossible, and this makes the analysis procedure easier. To investigate fundamentals of
epitaxial growth in the gas phase, we developed an in situ x-ray diffractometer that combines
an x-ray goniometer and reactor chamber [1], and used it to analyze surface structures ofindium phosphide (InP) [2].
Due to high partial pressure of V-elements, it is difficult to obtain good-quality epitaxial
films in MBE, and surface structures in the growth environment are poorly understood. We
investigated InP (001) surfaces grown by MOVPE in a hydrogen environment. Figure 1
shows intensity distribution of a reconstructed InP (001) surface in reciprocal space. Filled
symbols show the points where Bragg diffraction was observed, and crosses show where there
were no diffraction. Open circles indicate points where we cannot observe Bragg diffractions
because of the bulk Bragg diffraction. Obviously, fractional diffractions of (1/2 n) along the[-110] direction and integral diffraction spots along the [110] direction were observed,
suggesting (2×1) periodicity on the surface. Additionally, intensity variation along (1/2 m),(3/2 m) was observed, suggesting the surface model shown in Fig. 2.
[1] T. Kawamura et al., J. Cryst. Growth 221 (2000) 106.
[2] T. Kawamura et al., Appl. Phys. Lett. 77 (2000) 996.

Fig. 1. Intensity distribution in reciprocal space.
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Fig. 2. Model of (2×1) InP (001).

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Overview of Materials 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 to organic. The important feature of MSL is the effective sharing of nanofabricationand precise 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 into information processing devices based on neural functions.
Superconducting Thin Films Research Group
Creating new high-Tc superconductors using the molecular beam epitaxy method.
Superconducting Quantum Physics Research Group
Controlling quantum bits in superconductor as a step towards quantum computing, andcreating new magnetic devices using quantum dot arrays.
Nano-Structure Materials Research Group
Developing optical devices for the next generation using photonic crystals.
1.

2.

3.

4.

The four major results obtained in fiscal year 2000 are as follows.
The real-time monitoring of glutamate (Glu), which are typical neurotransmitters in the
cerebral cortex. By fabricating a special electrochemical Glu sensor array, we havesucceeded in real-time and multi-site monitoring of this neurotransmitter. This can be
regarded as the first step towards understanding the complex neural network in the brain.
High-quality electron-doped cuprate superconducting thin films were prepared bymolecular beam epitaxy (MBE) method for the first time. A reduction of the synthesis
temperature in MBE makes it possible to synthesize a high-quality thin firm, whichcannot be prepared by conventional methods. By investigating the properties of the films,
we should find a clear guiding principle for the search for new electron-doped
superconductor.
Ferromagnetism in quantum dot superlattices was theoretically predicted. A quantum dot
artificial crystal comprising 0.104-!m-wide InAs quantum wires has flat bandcharacteristics. By changing the electron filling of the band, we show that the crystal canbe switched from a ferromagnetic to a paramagnetic state and vise versa.
The single-mode, low-loss transmission was achieved in a two dimensional photonic
crystals. A photonic crystal, which is an artificial periodical structure consisting ofdifferent refractive-index materials, is expected to lead to smaller optical devices andlarger scales of integration. We proposed and fabricated line-defect two-dimensional
photonic crystals on the SOI (silicon on insulator) structures, and demonstrated thecapability of low-loss transmission under the single-mode condition.
The details of these accomplishments will be described in the following pages.

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Real-Time Monitoring of Neural Activity in the Brain
Nahoko Kasai, Yasuhiko Jimbo, and Keiichi Torimitsu
Materials Science Laboratory
The brain, which consists of neurons and many other different types of cell in a complex
network, provides efficient functions including transfer, storage and other forms of processingof a large quantity of information. Numerous attempts have been made to understand thesefunctions, however, few studies have been able to obtain real-time two- or three-dimensional
information with precision and high special resolution, which is essential if we are tocomprehend how the brain operates.
The release of neurotransmitters from neurons and their distribution are also important
issues in terms of understanding the mechanisms of memory and learning. However, few
studies have succeeded in monitoring the distribution of neurotransmitters themselves. Rather,reports have described the distribution of receptor subunits, which do not inform us of theactivity of the receptor and its dynamics. We focus on glutamate (Glu), one of theneurotransmitters in the cortex or hippocampus and have monitored the real-time Glu
concentration with a view of imaging and animating its two-dimensional distribution.
In this study, we have succeeded in monitoring the Glu concentration at multiple
positions in a hippocampal slice simultaneously [1]. We fabricated an electrochemical Glu
sensor array by modifying an electrode array (each size: 50×50 µm2) with enzymes and anelectron transfer mediator. We then placed the cultivated slice on the array and measured the
Glu concentration at selected sensors in the array. When we introduced a stimulant into theexternal medium, the sensors indicated the different amounts of Glu released as a result of thereceptor stimulation (Fig. 1). This result demonstrates the diversity of the receptors, theirdistribution and their dynamics. Our glutamate sensor array could prove to be a powerful toolfor understanding the role of glutamate in the brain. We will continue our work in order torealize the imaging of its distribution.
[1] N. Kasai et al., Neurosci. Lett. 304 (2001) 112.

Fig. 1. Glutamate concentration profiles at different positions in hippocampus.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Electron-Doped High-TC Superconducting Thin Films
Grown by Molecular Beam Epitaxy
Shin-ichi Karimoto and Michio Naito
Materials Science Laboratory
High-TC superconductors are classified as hole-doped or electron-doped and there seems
to be apparent asymmetry between the two classes. Hole-doped superconductors are major,
and their highest TC is 135 K. Electron-doped superconductors are minor (only two kinds),
and their highest TC is 40 K. This raises two important questions: why these TC values are so
different, and whether or not superconductivity mechanism is the same. To answer thesequestions, it is highly desirable to find new electron-doped superconductors and obtainhigh-quality single-crystalline thin films. Recently, we have succeeded in the MBE-growth of
single-crystalline films of the following two electron-doped superconductors that are difficult
to obtain by bulk synthesis.
(1) (Sr, La)CuO2 (TC =40 K)
Infinite-layer compounds have the simplest structure among high- TC superconductors(see Fig. 1(a)). However, despite this simple structure and the fact that they are theelectron-doped superconductors with the highest TC, they have been studied very little. This isbecause the synthesis of these compounds requires a high pressure of above 2.5 GPa. MBE
enables us to synthesize this high-pressure phase via an epitaxial effect. Figure 1(b) shows the!-T curve of our single-crystalline (Sr, La)CuO2 thin film grown on a special substrate(KTaO3). The low resistivity and metallic behavior indicate excellent crystallinity [1].
(2)T’- (La, Ce)2CuO4 (TC =30K)
The other kind of electron-doped superconductor is represented by (Ln,Ce)2CuO4. This
structure is formed with Ln=Pr, Nd, Sm, Eu, Gd, by using the conventional solid-state
reaction method. The maximum TC (25 K) of this series is achieved with (Pr,Ce)2CuO4 and(Nd,Ce)2CuO4. Low-temperature MBE growth makes it possible to synthesize (La,Ce)2CuO4,
which attains the highest TC in this group (30 K). Moreover, we found that there is a tendency
for the TC to become higher as increasing the ionic radius of the Ln elements. This gives us aclear guiding principle in the search for new high-TC superconductors [2].
[1] S. Karimoto et al., submitted to Appl. Phys. Lett.
[2] M. Naito and M. Hepp, Jpn. J. Appl. Phys. 39 (2000) L485.
(a)

(b)

Fig. 1. (a) Crystal structure and (b) best ! -T curve for (Sr, La) CuO2 thin film.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Novel Material Design in Quantum Dot Superlattices
Hiroyuki Tamura and Hideaki Takayanagi
Materials Science Laboratory
If we consider a quantum dot (QD) as a building block and put it on a site of lattice, we
can create an artificial crystal called quantum dot superlattice. There are several advantages ofusing semiconductor dots in making artificial crystals. First, the lattice structure can be widely
chosen. One can fabricate a lattice structure which does not exist in nature. Second, theelectron filling can be freely modified. As a consequence, various types of interesting
electronic properties can be expected. We have proposed that specific types of quantum dot
superlattice exhibit ferromagnetism which should be observable in experiment [1].
Recently, we have presented the theoretical design of quantum dot superlattice exhibiting
ferromagnetism by using a quantum-wire network shown in Fig. 1 [2]. The electronic
structure calculations based on a local spin density approximation (LSDA) show that ourdesigned QD artificial crystal from a structure comprising the crossing 0.104-!m-wide InAs
quantum wires forms an effective Kagome lattice having a flat band. Our examined QD
artificial crystal has the ferromagnetic ground state when the flat band is half-filled as shownin Fig. 2, even though it contains no magnetic elements. We have also demonstrated that theferromagnetic and paramagnetic states can be freely switched by changing the electron filling.
By extending the idea of dot superlattices, one can think of other interesting possibilities
of artificial materials. In the near future, the semiconductor nano-technology may allow us torealize other interesting electronic properties, such as superconductivity, in quantum dot
superlattices.
[1] H. Tamura, K. Shiraishi, and H. Takayanagi, Jpn. J. Appl. Phys. 39 (2000) L241.
[2] K. Shiraishi, H. Tamura, and H. Takayanagi, Appl. Phys. Lett. 78 (2001) 3702.

Fig. 1. The effective Kagome crystal we examined.
The crossing quantum wire is InAs
and the barrier region is In0.72Ga0.28As
with barrier height of 0.21eV.

Fig. 2. A cross-sectional view of LSDA-calculated
spin density of ferromagnetic states.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Successful Fabrication of 2D Photonic Crystals
Masaya Notomi, Akihiko Shinya, and Itaru Yokohama
Materials Science Laboratory
A photonic crystal is an artificial periodical structure composed of different
refractive-index materials and its use is expected to lead to the development of smaller opticaldevices and larger scales of integration. We have been focusing on the SOI (Silicon On
Insulator) structure and have been researching 2D photonic crystals in cooperation with
Telecommunications Energy Laboratories.
We have fabricated vertical holes with a triangular lattice pattern in a 200 nm-thicksilicon layer with a period of 400 nm. The structure of this 2D photonic crystal ischaracterized by silicon regions (high refractive index) and air regions (low refractive index)
in the vertical holes that are periodically arranged along the horizontal plane of the siliconlayer. The propagated light is vertically confined in the silicon layers because silicon has ahigher refractive index than silicon oxide or air. Measurements have revealed that a clear
photonic bandgap (a feature of photonic crystals that functions as an optical insulator) is
formed in the optical-communications wavelength region [1]. We have also proposed awidth-varied line-defect structure that is applicable to the above structure. Figure 1 shows a
SEM photograph of the width-varied line-defect structure we fabricated. Measurement results,
such as the transmission-spectrum (Fig. 2), show that we have achieved low-loss transmission
under single-mode conditions for the first time [2].
In this research, we have demonstrated the 2D photonic crystal and line-defect structuresusing SOI structures. These structures are suitable as basic elements for ultra-small optical
integrated circuits.
[1] I. Yokohama et al., OECC 2000 (2000) 11B2-4.
[2] M. Notomi et al., Electron. Lett,. 37 (2001) 293.

Fig. 1. SEM viewgraph of fabricated linedefect waveguide structure.

Fig. 2. Tranmission spectra.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

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. The Quantum Solid State Physics Research Group and theWide-Bandgap Semiconductor Research Group are working in the following areas.
Quantum Solid State Physics Research Group(1) Carrier interactions in low-dimensional semiconductor heterostructures (two dimensional
carrier transport and correlation effects in high-mobility semiconductors, carrierinteractions in bilayer (electron-electron and electron-hole) systems, and interactions
between nuclear-spin and conduction electrons in semiconductors).
(2) Quantum electronic state control in quantum dot systems (electronic properties of verticaland lateral semiconductor quantum dots (artificial atoms and molecules), spin control inquantum dots, carrier dynamics of quantum dots, and fundamental properties ofsolid-state quantum computers using artificial molecules).
(3) Semiconductor nano-mechanical systems (fabrication of nano-mechanical structures andtheir characterization) and nano-probing (direct nano-scale imaging of electronic states by
low-temperature scanning-tunneling-microscopy (STM) technique).
Wide-Bandgap Semiconductor Research Group(1) High-quality GaN crystal growth (mechanism of GaN and facet-controlled crystal growthby MOCVD, high-concentration p-type doping, and device processing technology).
(2) GaN semiconductor device physics (electronic and optical properties of GaN quantum
well structures, electronic devices suitable for high-temperature operation, andshort-wavelength light emitting devices).
(3) Electron field emission in AlN cold cathode materials (field emission characteristics,
such as threshold field and available emission current, as a function of Si-dopant density).
Major results obtained this fiscal year 2000 are reported in the following pages. We
experimentally investigated Kondo effect caused by spin correlated transport in well-defined
semiconductor quantum dots. We successfully demonstrated the unitary limit Kondo effect,i.e., theoretical maximum in conductance. We also discovered novel aspect in Kondo effectthat appears when even number of electrons are involved. These results promise controllable
electron-spin correlation in quantum dots, leading to future “quantum correlated electronics”.
We have successfully imaged electron waves (Friedel oscillations) in real space byapplying low-temperature STM technique. Different from localized electron waves at surface
boundaries so far observed, our direct observations were carried out for conducting electronsin two-dimensional electron gas accumulated in near-surface region of InAs. We believe that
this technique will be indispensable for fully understanding ultimately small devices.
Besides conventional electronic and photonic device applications of nitride-based
semiconductors, we demonstrated novel property favored in wide bandgap materials, i.e.,highly efficient electron-field-emission in heavily Si-doped AlN. Available emission current
density obtained in our AlN has already exceeded the maximum value realized so far indiamond, which is exciting enough for future applications to field-emission display and so on.
‐20‐Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Novel Kondo Effect in Quantum Dots
Toshimasa Fujisawa and Satoshi Sasaki
Physical Science Laboratory
Quantum dots, in which electrons are confined by semiconductor nano-structures, show
the quantum mechanical duality (particle- and wave-nature) for the electrons; the number ofthe electrons in the quantum dot is precisely controllable and discrete energy states are formed
as a result of electron-wave interference. Moreover, many electron-spin related phenomena
have been investigated in quantum dots. Since the electronic states in quantum dot resemble
natural atoms, quantum dots are often called artificial atoms. The properties of quantum dotsthat can control a single electron-spin are promising for an application to the element(quantum bit) that realizes quantum information processing, such as quantum computers. In
order to explore the possibility of quantum gates that correlate quantum bits, Kondo effects inquantum dots are attractive for their spin correlated transport.
The Kondo effect in quantum dot is a quantum mechanical co-tunneling process causedby the electron-spin interaction between electrons in the quantum dot and electrons in the lead.
Even when the electron transport is restricted by Coulomb blockade effect, an electron canflow through the dot by making spin correlated singlet state if the dot has an electron-spin.
The Kondo effect normally appears when the dot has odd number of electrons (total spin 1/2),
but is absent when the dot has even number of electrons (total spin 0). The conductancethrough the dot is enhanced by the Kondo effect as opposed to classical Coulomb blockade
effect, and at a low temperature the conductance is expected to reach 2e2/h, which is called
unitary limit (see Fig. 1(a)). We successfully achieved the unitary limit Kondo effect andconfirmed the coherent electron transport for the Kondo effect from electron interference
experiments [1]. Furthermore, application of magnetic field allows us to tune the dot to thespecific spin degenerated state. Even if the number of electrons is even (N = 6 for Fig 1(b)),
energy degeneracy between spin singlet state and triplet state makes the spin correlation more
possible, and thus remarkable novel Kondo effect shows up [2]. The series of experiments
indicate that the electron-spin correlation can be well controlled in a quantum dot.
This work is collaborated with Prof. L. P. Kouwenhoven at TUDelft, Prof. S. Tarucha at
University of Tokyo (also at ERATO and NTT) and co-workers.
[1] W. G. van der Wiel et al., Science 289 (2000) 2105.
[2] S. Sasaki et al., Nature 405 (2000) 764 .

Fig. 1. (a) Temperature dependence of the conductance (Schematic). (b) Novel Kondo effectappears for even number of electrons (N = 6), if single and triplet states aredegenerated.
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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Friedel Oscillations in 2D Electron Gas Systems
at Semiconductor Surfaces
Kiyoshi Kanisawa, Hiroshi Yamaguchi, and Yoshiro Hirayama
Physical Science Laboratory
The operational principle of the semiconductor electronic devices fabricated so far isbased on the control of the number of electrons passing through the active part of devices.
This principle utilizes the feature of electrons as material particles, which had been the
excellent description in the classical theory of physics. The recent progress in thesemiconductor processing techniques allows the accurate manufacturing of ultimately small
devices whose size is in the range of tens of nanometers. In these devices, we need to take
into account the other feature of electrons, which is that they act as matter waves. This feature
is one of the most significant conclusions drawn from the principle of quantum mechanics.
Recently, there have been many device proposals based on novel operational concepts arisingfrom this quantum mechanical feature. To understand the transport phenomena in these kindsof devices in detail, the behavior of electrons as matter waves should be directly observed.
From this point of view, we have successfully imaged electron waves in real space byapplying low-temperature scanning tunneling microscopy (STM) and our unique crystal
growth technique that enables the preparation of an electrically conductive and extremely flat
surface of InAs [1,2].
Figure 1 shows local density of states (LDOS) images at a defect scatterer on the InAs
surfaces with different electron energies. Wave patterns made up of concentric circles areclearly imaged in the vicinity of the isolated defect. From the nature of oscillation damping,
we can conclude that this is the so-called Friedel oscillation due to electrons being laterally
scattered by the defect. By observing the bias voltage dependence, the effective mass wasestimated to be 0.043 m0, which is in good agreement with previous reports. Our detailed
analysis indicates that the observed oscillations are caused by the scattering of thetwo-dimensional electron gas accumulated in the near-surface region of the InAs surfaces.
[1] H. Yamaguchi et al., Jpn. J. Appl. Phys. 38 (1999) 635.
[2] K. Kanisawa et al., Phys. Rev. Lett. 86 (2001) 3384.

Fig. 1. LDOS images in the vicinity of a point scatterer
on epitaxially grown InAs (111)A surfaces.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Large Electron-Field-Emission from Aluminum Nitride
Makoto Kasu and Naoki Kobayashi
Physical Science Laboratory
Aluminum nitride (AlN) has negative electron affinity. Therefore, it is very promising forfield emission. Field emission is mainly of interest in its application to field-emission displays,
thin flat-panel displays suitable for moving-pictures, and to micro vacuum tubes made ofsemiconductor microstructures suitable for high-frequency amplifiers. However, the AlN
crystal quality reported so far has not been good enough for field emission, and, because thereported AlN was undoped and its free-electron density was low, the reported current densityof the field emissions was much lower than that of diamond.
We chose a silicon-carbide (SiC) substrate which has the same lattice constant in plane
and the same thermal expansion coefficient as those of AlN. We then grew AlN crystal at
1100oC by MOVPE and this produced AlN crystal of high quality. The full-width at half
maximum of the (0002) x-ray rocking curve was less than 100 sec. The value is the narrowest
ever, showing that we have grown the best quality AlN. We found that, as the Si dopant
density in AlN is increased, the electric field necessary for field emission is decreased asshown in Fig. 1 [1]. The mechanism is shown in Fig. 2. The doped Si supplies the electronsnecessary for field emission, and the Si atoms form the impurity level. The electrons aresupplied through the impurity band to the surface. Further, we found that ridge structures
whose top width is of the nanometer order are formed spontaneously by heavy Si doping (seeinside-cover) [2]. The ridge-structure formation lowers the energy barrier necessary for fieldemission by about 2 eV. As a result, using heavily Si-doped AlN, we have obtained a2
field-emission current density of 66 mA/cm , twice that for diamond. In a basic structure for afield emission display, we observed red, green, and blue light from phosphors excited byfield-emitted electrons (see inside-cover). Its luminance was 1200 cd/m2, which is intense
enough for a practical display.
[1] M. Kasu and N. Kobayashi, Appl. Phys. Lett. 76 (2000) 2910.
[2] M. Kasu and N. Kobayashi, Appl. Phys. Lett. 78 (2001) 1835.

Fig. 1. Si-density dependence of field emission
characteristics.

Fig. 2. Mechanism of large field emission.

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

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 and Optical Device Physics
Research Group are engaged in the subjects listed below.
Quantum State Control Research Group(1) Quantum communication and information processing (proposal and verification of a newquantum cryptography, studies on quantum protocols, quantum entanglement, andquantum computing).
(2) Atom optics (experimental and theoretical studies on Bose-Einstein condensation ofalkali atoms, and control of new quantum states by laser lights).
Ultrafast Optical Physics Research Group(1) High-irradiance soft X-ray generation from femtosecond laser-produced plasma and its
application to materials science (demonstration of high-irradiance soft X-ray pulse
generation and table-top soft X-ray laser, clarification of soft X-ray generation
mechanism, and demonstration of time-resolved soft X-ray spectroscopy).
(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 (optical Rabi oscillations ina zero-dimentional exciton, experimental study of excitonic properties of quantum dots,
spin-polarized electron transport in quantum wires).
(2) Optical properties in nitride-semiconductors and their device applications (opticalproperties of nitride quantum wells, including excitonic and piezo-electric effects, andnitride photo-conductive detector).
(3) Nano-scale fabrication process for photonic crystal materials (dry etching process fordamage-free surfaces of GaAs and GaN, and design and fabrication of photonic crystal
structures).
Major results obtained this fiscal year 2000 are reported in the following pages. We
investigated strong gain saturation behavior in fiber optical parametric amplification anddemonstrated its application to noise suppression and optical limiter operations. Parametric
process in optical fiber is promising for the generation of quantum entangled photon twins forquantum communications.
Nanostructure-array targets were employed to create larger-volume plasm withhigh-local-density, compared with those from flat target, in X-ray generation fromfemtosecond-laser-produced plasma, resulting in large soft x-ray conversion efficiency as wellas suppression of broadening of generated x-ray pulse duration.
We demonstrated long-lived exciton coherence more than 40 ps in a single isolated
InGaAs quantum dot. Favored by this long-lived coherence, we clearly observed exciton Rabi
oscillation, i.e., coherent population flopping induced by the strong coupling light resonant toexcitonic discrete level. This promises the coherent control of the quantum states insemiconductor quantum dots applicable to quantum computation.
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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Optical Parametric Amplification in Fiber
Kyo Inoue and Takaaki Mukai
Physical Science Laboratory
Quantum correlated two photons (entangled photon-pair) have the unique feature that thephoton states are undetermined before measurements while the state of one photon is uniquelydetermined when the other photon state is measured. Utilizing entangled photon-pairs, novelcommunications based on quantum nature of photons (e.g., quantum cryptography) is possible.
For generating entangled photon-pairs, parametric down conversion via the second-order
optical nonlinearity has been widely used. However, this scheme has disadvantages for fiber
communication systems, such that (1) available wavelengths are limited to short wavelength
bands (< 1 !m), and (2) coupling efficiency to fiber is quite low because bulk materials areused.
We study optical parametric amplification process in optical fibers, aiming at generating
entangled photon-pair suitable for fiber communications. When pump light is input into afiber, signal and idler lights are generated in the either wavelength side of the pump via
four-photon mixing process (Fig. 1) [1]. These photons are quantum correlated. They are
generated at wavelengths suitable for fiber communications (1.5-!m band), and they can bedirectly coupled to fiber transmission lines without any coupling loss.
We are investigating a fiber optical parametric amplifier where signal light is injected into
the fiber together with pump light. What we have done are, (1) experimental demonstrationand theoretical calculations of unique saturation characteristics (Fig. 2), different fromconventional optical amplifiers, that the signal output power increases, reaches a peak value,
and then decreases, as the input signal power increases [1], (2) demonstration of noise
suppression effect and low noise property operated in the output peak region (indicated by thearrow in Fig. 2), (3) observation and clarification of mechanism of spectral hole burning, (4)demonstration of optical limiter operations [2,3]. These works indicate that fiber parametricamplifier is applicable to ultra-fast optical functional devices accompanied with significant
signal gain. Based on the above results, we will aim at generating entangled photon-pair in thecommunication wavelength band.
[1] K. Inoue and T. Mukai, Opt. Lett. 26 (2001) 10.
[2] K. Inoue, Electron. Lett. 36 (2000) 1016.
[3] K. Inoue, IEEE Photon. Technol. Lett. 13 (2001) 338.

Fig. 1. Fiber output spectrum(only pump light is injected).
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Fig. 2. Output characteristics
of parametric amplifier.

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Efficient X-ray Generation from Femtosecond-Laser-Produced
Plasma on Nanostructure-Array Targets
Tadashi Nishikawa and Hidetoshi Nakano
Physical Science Laboratory
X-ray generation from femtosecond-laser-produced plasma is an attractive way to obtainshort pulse x-rays. However, due to the formation of solid density plasma at a target surface,
the interaction depth of the femtosecond laser pulses is restricted to skin depth, i.e., around 50
nm, and thus the conversion efficiency is limited. In order to improve the conversion
efficiency, a double-laser-pulse excitation technique is commonly used. After the expansionof the preformed plasma created by the first laser pulse, the expanded low-density plasma isheated effectively by the intense second laser pulse, and large x-ray conversion efficiency is
obtained. But with this technique, the generated x-ray pulse duration is broadened from 5 ps(single pulse excitation) to around 100 ps due to the slow cooling rate of low-density plasma.
To overcome these problems, we utilized nanostructure-array targets to extend the interaction
depth of the laser pulse to around 20 !m. Large-volume plasma with high-local-density iscreated on these targets by a single laser pulse excitation, and large soft x-ray conversion
efficiency enhancement can be achieved while keeping the short x-ray pulse duration.
Two types of nanostructure-arry targets were used in our experiment. One is ananohole-array structure [1]. This structure was made by utilizing the anodic oxidation of analuminum plate. By a self-ordering process, an anodic-alumina layer that has central,cylindrical, and uniformly sized pores that run perpendicular to the surface is formed on thealuminum plate. The pore diameter is around 90 nm and the distance between the adjacentpores is 100 nm. The other structure is a nanocylinder-array structure [2]. After filling up thealumina nanoholes with Au by electrodeposition, the alumina part was removed (Fig. 1). The
cylinder diameter is 80 nm and the cylinder heights are 9 and 18 !m.
These targets were irradiated with 100 fs laser pulses at the peak intensity of 1.5×1016
W/cm2, and generated soft x-ray fluence spectrum was measured (Fig. 2). Around a 50-10
fold soft x-ray fluence enhancement compared with a conventional plane surface target wasachieved at 5-25 nm wavelengths. X-ray pulse duration on both nanostructure-array targets
was 17 ps, which is shorter than that obtained by the double-laser-pulse excitation techniqueon a plane surface target or by synchrotron radiation. The x-ray pulse peak intensity on thenanostructure-array targets was 5-7 times higher than that on a plane surface target.
[1] T. Nishikawa et al., Appl. Phys. Lett. 75 (1999) 4079.
[2] T. Nishikawa et al., International Conference on X-ray Lasers 2000.

Fig. 1. SEM image of a Au nanocylinder-array target’s side view.

Fig. 2. Soft x-ray spectral fluence from a Au
nanocylinder-array target (solid line)
and from a gold foil target (dotted line).
‐26‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Exciton Rabi Oscillation in Single Quantum Dot
Hidehiko Kamada and Hideki Gotoh
Physical Science Laboratory
Optical Rabi oscillation is the most fundamental examples of coherent nonlinear
light-matter interactions. It is the essential physics that coherent optical control of thequantum states relies on. Excitons in semiconductor quantum dots (QD's) are above allpromising elements for such coherent manipulation because of long-lived coherence favoredby discrete energy level structure. We observed the exciton Rabi oscillation in QDs.
In a single isolated InGaAs dot, an excited state resonance was chosen as upper level of
relevance. Upon resonant excitation, the exciton emission was found to split into doublet forincreasing excitation density [1]. This splitting increased proportional to the electric field asexpected for Rabi splitting (Fig. 1 left). To observe the oscillation in time-domain, a single-dot exciton
dipole interferometry was then conducted. Under low excitation, the coherent dipole
oscillation induced by the first pulse persists as long as 40 ps: Correspondingly the dipole
interference fringe decay with this time constant was observed (Figs. 1(a) and 1(b)). This
demonstrates a long-lived exciton coherence. As the excitation increased more than one orderof magnitude, the radiation induced not only the dipole oscillation but also the population
oscillation, leading to a mixing of the Rabi frequency into the dipole interference fringe (Fig.
1(d)) as well as another oscillatory behavior with a period of 10-20 ps in the fringe envelope(Fig. 1(c)). The frequency of this slowly varying oscillation was found to increase
proportional to pulse area, manifesting the relevance of the Rabi oscillation [2]. Observationof the coherent population flopping promises the coherent control of the quantum states insemiconductor QDs.
[1] H. Kamada et al., ICPS25, Osaka, (2000) H169.
[2] H. Kamada et al., CLEO Pacific Rim 2001, Chiba, (2001) ThG4-3.

Fig. 1. Energy splitting of exciton PL for increasing excitation density (left). Exciton
interference as functions of pulse-pair interval (right): (a) fringe envelopes for a power
density P1 (0.067 !J/cm2 /pulse) and (b) decomposed fring near 30 ps, (c) envelopesfor 12 P1 (0.8 !J/cm2 /pulse) and (d) fringe near 0 ps.

‐27‐

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

International Symposium on Carrier Interactions in Mesoscopic Systems
The symposium was held on February 13th and 14th, 2001, at the NTT Atsugi R&D
Center and was organized by New Energy and Industrial Technology Development
Organization (NEDO), Core Research for Evolutional Science and Technology - Japan
Science and Technology Corporation (CREST-JST), and NTT Basic Research Laboratories.
Carrier interactions in layer and nano structures have attracted much interest because they
will be important to realize novel systems, possibly leading to quantum computing and carrier
superfluidity. In this symposium, we tried to cover many areas from science and technology
using the single key-word of carrier interactions for classification rather than the moreconventional terms, semiconductor, superconductor and device physics. NTT Basic ResearchLaboratories have led this field, and the aim of the symposium was to gather together leading
scientists to discuss the most recent topics.
Oral sessions consisted of 19 presentations by invited speakers and the main members of
the NEDO and CREST collaborating research teams. The plenary presentation for carrierinteractions in layer and nano semiconductor systems was given by Prof. K. von Klitzing(Max-Planck-Institut), who discovered the quantized Hall effect and won a Nobel Prize inPhysics in 1985. This was followed by theoretical and experimental reports on electron
bilayer systems, electron-hole proximity systems, carrier interactions in layer structures,electron spin, and nuclear spin. In particular, electron bilayer systems were highlighted as
ideal systems for the study of carrier interactions. Furthermore, recent topics related to spinblockade and the Kondo effect were discussed as examples of carrier interaction effects inquantum dots. Process and growth technologies toward the fabrication of structures suitablefor carrier interaction studies and nanoprobe measurements were also presented. Finally, we
discussed approaches towards the realization of solid-state quantum computing, which isperhaps the most exciting target for applying carrier interaction effects. Poster sessions
consisted of 46 contributed presentations. They covered the fabrication of nano structures,quantum Hall effects, carrier interactions in bilayer systems, Kondo effect in quantum dots,
control of electron spin in semiconductors, and proposals for solid-state quantum computation.
The number of participants was 142 (97 from outside of NTT). Participants were strongly
impressed by the high quality of the symposium.

Plenary presentation by Prof. Klaus von Klitzing (center), welcome address by Dr. Sunao
Ishihara, director of NTT Basic Research Laboratories (left), and oral session at the
symposium (right).

‐28‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Advisory Board
The Advisory Board, an external evaluation committee for NTT Basic ResearchLaboratories (BRL), convened for the first time for two days, February 15 and 16, 2001. The
Advisory Board seeks to (1) evaluate research plans and achievements objectively and in atimely manner, (2) dispatch information effectively to the world through board members, and(3) reinforce systematic research cooperation with the board-member organizations.
On the first day, executive managers and group leaders outlined the research activities of
BRL to give board member a grasp of the progress of BRL’s research and its research strategy.
After that, board members were given a guided tour of the facilities. On the second day, theyheld discussions on the basis of the information obtained on the first day in a closed session.
Then, the advisory board committee reported on the management of BRL.
The board evaluated us very well, commenting that the research level is generally high,the research environment exceeds international standards, and equipment is maintained well.
However, they pointed out that certain research fields are getting weak due to the departure ofsenior researchers. Regarding management, we received many unsparing but constructive
suggestions. Among them, technical engineers are required because of technical succession,
continuous reservation of young talent is important, and laboratories should be activated morethrough more internal competition and cooperation between groups.
Because this was our first experience with an external evaluation, we spent much time forpreparation. Meanwhile, this was a very precious opportunity: we received an objective
evaluation of our research level and many suggestions, which may serve as indicators of
future directions. About the Advisory Board itself, although board members were favorably
impressed, they commented that the contents should not be selected beforehand and all actual
conditions should be shown. For this purpose, the program is too short. Furthermore, theycommented that the evaluation be done every year. We decided that next board committee
will convene in a year and half. This interval is shorter than we had planed.

Board Members Affiliation
Prof. Claeson
Chalmers UTProf. Devoret
CEA Saclay
Prof. Flytzanis
Ecole Normal
Prof. Mooij
Delft UT
Prof. Ploog
P.D. Inst.
Prof. Tang
Cornell U
Prof. von Klitzing MPI

Field
Superconductor devices
Mesoscopic physics
Non-linear optics
Quantum computer
Nanostructures
Quantum optics
Quantum physics‐29‐Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Science Plaza 2001
"Science Plaza 2001", the annual open house event of NTT Basic Research Laboratories,
was held from February 13-14, 2001, at the NTT Atsugi R&D Center. The International
Symposium on Carrier Interactions in Mesoscopic Systems (CIM2001) was held concurrently.
Participants of "Science Plaza 2001" were allowed to attend the CIM opening remark by Dr.
Sunao Ishihara, Director of NTT Basic Research Laboratories, and the CIM plenary talk by
Dr. K. von Klitzing, Physics Nobel Laureate.
In "Science Plaza 2001", the activities of NTT Basic Research Laboratories were
demonstrated via presentations in a "Poster Session", "Laboratory Tour", and "Video Theater".
The "Poster Session" featured 41 presentations on the topics of materials and physics, and theactual researchers directly explained and discussed these topics with the participants. The"Laboratory Tour" featured extremely low temperature technology, the creation of X-ray
lasers, the synthesis of high-Tc materials by molecular beam epitaxy, a clean room tour and apeta-media tour, and we showed our research equipment and facilities to the participants. The"Video Theater" featured "Mesoscopic Superconductors―A Perspective from an International
Symposium" and "Novel Trend ― Mysteries of Quantum Theory Clarified byExperiments", and we demonstrated some of our research activities with pictures.
We had about 200 participants at "Science Plaza 2001" even though the NTT Atsugi R&D
Center is located about 2 hours far from the center of Tokyo. In addition, some participants
came from cities more than 300 km away (Sapporo, Sendai, Nagoya, Kyoto, Osaka, andKohchi) by plane, train, and/or bus. Many of the CIM participants also attended "Science
Plaza 2001". Since so many people requested to join the "Laboratory Tour", we preparedadditional tours. The participants gave us many hints and insights for future research andmany words of encouragement for uninterrupted basic and fundamental research in materials
and physics. We would like to again thank all participants of "Science Plaza 2001".

‐30‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

List of Award Winners (Fiscal 2000)

The 8th Japan Societyof Applied Physics
Young Scientist Awardfor the Presentation of
an Excellent Paper

K. Kumakura"High Hole Concentration
Realized by Mg-doped InGaN
and InGaN/GaN Superlattices"

Sept. 3,
2000

JJAP Paper Award, the22nd Paper Award of
the Japan Society ofApplied Physics

H. Kageshima
K. Shiraishi
M. Uematsu"Universal Theory of Si
Oxidation Rate and Importanceof Interfacial Si Emission"

Sept. 4,
2000

Electronics Letter
Paper Award(The Institute ofElectronics, Information
and Communication
Engineers)

O. Hanaizumi*
Y. Sakurai*
Y. Aizawa*S. Kawakami*
E. Kuramochi
S. Oku*Tohoku Univ.

"Embedding of III V Compound
Semiconductors into 3D Photonic
Crystals"

Oct. 2,
2000

Matsuo Science Prize(Matsuo Foundation)

Y. Yamamoto"Fundamental Research on Opticaland Quantum Physics"

Oct. 18,
2000

H. Nakashima"Switchable Induced Circular
Dichroism of Chiral Aggregatesof Poly(alkylalkoxyphenylsilane)
Bearing Remote Chiral Groups"

Feb. 23,
2001

K. Furukawa"End-Grafted Polysilane―Approach for Single Polymer
Science and Electronics"

Mar. 7,
2001

ISPA AWARD(Internet International
Symposium on SiliconContaining Polymers
and Applications)

Poster Award(First International
Conference on
Molecular Electronics
and Bioelectronics)‐31‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

List of In-House Award Winners (Fiscal 2000)

NTT R&D Award

H. Hibino
Y. OnoY. Homma
Y. Takahashi
A. Fujiwara"Integration of AtomicallyControlled Nanostructures andSingle Electron Functionality"

Dec. 19,
2000

Award forAchievements by
Director of Basic
Research
Laboratories

T. Kawamura
Y. Watanabe
Y. Utsumi
K. Uwai"Surface Reconstructions of
Semiconductor Materials in GasPhase Growth by Using Grazing
Incidence X-ray Diffraction"

Mar. 26,
2001

Award forAchievements by
Director of Basic
Research
Laboratories

H. Shibata"Observation of Josephson Plasma
in High-Tc Superconductors"

Mar. 26,
2001

Award forAchievements by
Director of Basic
Research
Laboratories

K. Kanisawa
H. Yamaguchi
Y. Hirayama"Direct Imaging of LowDimensional Electron Waves in
Semiconductors"

Mar. 26,
2001

Award forAchievements by
Director of Basic
Research
Laboratories

M. Kasu
N. Kobayashi"Large Electron Field Emission
from Aluminum Nitrides"

Mar. 26,
2001

S. Sasaki"Kondo Effect in an Integer-Spin
Quantum Dot"
Nature 405 (2000) 764.

Mar. 26,
2001

Award for
Excellent Papers by
Director of BasicH. TamuraResearch
Laboratories"Ferromagnetism in Semiconductor
Dot Array"
Jpn. J. Appl. Phys. 39 (2000) L241.

Mar. 26,
2001

Award for
Excellent Papers by
Director of Basic
Research
Laboratories‐32‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

List of Visitors’ Talks (Fiscal 2000)

l. Device Physics
Date

Speaker

Affiliation"Topic"April 13

Prof. Seiji Takeda

May 10Dr. Neil Zimmerman

May 18

Prof. Ernst Bauer

June 29

Dr. Stefan Heun

July 13

Dr. Matthew P. Halsall

Aug. 25

Prof. Pulickel M. Ajayan

Sept. 18

Dr. C. N. McKinty

Nov. 1

Prof. Robert L. White

Jan. 17

Prof. Otto Zhou

Jan. 19

Dr. Stefano Fontana

Jan. 19

Dr. Toshihisa TomieJan. 24

Dr. Dean Collins

Jan. 24

Dr. Keith Schwab

Jan. 31

Prof. Stoyan S. Stoyanov

Osaka University"Novel fabrication process of Si nano structure andoxidation"
National Institute of Standards and Technology,
USA"Long-term charge offset and glassy dynamics in
SET transistors"
Arizona State University, USA"SPELEEM"
Sincrotrone Trieste ELETTRA, Italy"Nanospectroscopy on InAs nanocrystals"
University of Manchester, UK"Si-Ge self assembled quantum dots"
Rensselaer Polytechnic Institute, USA"Growth and structure of carbon nanotubes"
University of Surrey, Guildford, UK"Investigating the use of sputtered !-FeSi2 for solar
cell applications"
Stanford University, USA"A review of the research at the Stanford Center for
Research on information storage materials"
University of North Carolina, USA"Growth and application of carbon nanotube"
Sincrotrone Trieste ELETTRA, Italy"The spectromicroscope of Elettra"
Electrotechnical Laboratory"Photoelectron micro-spectroscopy with a laser-plasma
X-ray source"
The Advanced Research and Development Activity,
USA"Details of ARDA's program in quantum information
science"
The Laboratory for Physical Science, USA"Quantum computing research at the laboratory forphysical sciences"
Institute of Physical Chemistry, Bulgarian Academyof Sciences, Bulgaria"A shape of the steps at the surface of Si crystal with
SiO2 inclusions"‐33‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

March 5

Prof. Takashi Morie

March 27

Prof. K. P. Jain

Hiroshima University"Image-recognition integrated circuit systems basedon brain-like processing"Indian Institute of Technology, Delhi, India"Raman and photoluminescence spectroscopy ofsilicon nanostructures"

ll. Materials Science
Date

Speaker

Affiliation"Topic"April 5

Prof. Yasuhiko Arakawa

April 24

Prof. Koichi Kusakabe

May 19Mr. Kensuke Honda

June 29

Prof. Yang Yang

July 21Dr. Jonathan Selinger

July 27

Dr. Rajeshwar P. Sharma

Aug. 17

Prof. Yehoshua Levinson

Aug. 29

Prof. Yasutomo J. Uemura

Sept. 4

Prof. Yoseph Imry

Sept. 8Dr. Mark Johnson

Sept. 11

Dr. Andrei Filip

The University of Tokyo"Semiconductor nano-structures: from 'crystal
growth', 'optical properties', to 'quantum devices'"
Niigata University"Strong correlation effects based on anomalous
density of states"
The University of Tokyo"Surface-controlled diamond electrodes and theirapplications"
University of California, Los Angels, USA"Polymer morphology formation and influence topolymer-based LED device performance"
Naval Research Laboratory, USA"Theory of chiral order in polymers and lipid
microstructures"
University of Maryland, USA"Ion channeling studies in high-Tc cuprates and
CMR manganites - Direct experimental evidence ofelectronic phase seperation"
Weizmann Institute, Israel"Dephasing in quantum dots due to capacitive
coupling with point contacts"
Columbia University, USA"Condensation and phase separation of high-Tc
superconductors inferred from the superfluid
density"
Weizmann Institute, Israel"The observability of quantum- and shot-noise andlow-temperature 'decoherence'"
Naval Research Laboratory, USA"Spin injection and detection in a ferromagnetic
metal / 2DEG structure"
University of Groningen, The Netherlands"Direct experimental comparison between theelectrical spin injection in a semiconductor and in a
metal"‐34‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Oct. 6

Dr. Toru Matsuyama& Dr. Andreas Richter

Oct. 19

Dr. Lambert Alff

Nov. 24

Prof. Shigemasa Suga

Dec. 5

Dr. Han Chunxi

Dec. 25

Prof. P. Ganguly

Jan. 18

Prof. Emilio E. Mendez

Jan. 18

Dr. Gerald Bastard

Jan. 19

Dr. Takeshi Nakanishi

March 8

Prof. ChristianSchoenenberger

March 15

Prof. Kei Murakoshi

March 16

Prof. Wei Yao Liang

March 22

Dr. Makoto Osanai

Hamburg University, Germany"Spin-orbit interaction in InAs 2DEG andspin-injection experiment"
University of Cologne, Germany"Pairing symmetry and pseudogap in hole-doped andelectron-doped high-Tc cuprates"
Osaka University"High-energy & high-resolution photoemission
spectroscopy of strongly correlated electron systems-separation of bulk and surface electronic structures"
Keio University"Systematic injection of kainic acid stimulates
expression of NCAM-H in reactive astrocyte of rat
hippocampus"
National Chemical Laboratory, India"Resistivity and metal-insulator transition: Theinterpretation of resistivity values in complex oxides"
State University of New York at Stony Brook, USA"The uniqueness of the InAs-GaSb heterojunction,and its practical consequences"
Laboratoire de Physique, Ecole Normale Superieure,France"Polaron levels and energy relaxation in InAs
quantum dots"
Delft University of Technology, The Netherlands"Electrical transport in carbon nanotubes"
University of Basel, Switzerland"Electrical and mechanical properties of carbon
nanotubes"
Osaka University"Characteristics of photo-induced metal nanostructure and their functionalities"
Cavendish Laboratory, University of Cambridge,
UK"The fascination of high Tc superconductivity"
Tokyo Medical and Dental University"Ca ion and synapse transmission"lll. Quantum Electron Physics
Date

Speaker

Affiliation"Topic"June 13

Mr. Stuart Midgley

July 24

Prof. Leo Kouwenhoven

The University of Western Australia, Australia"Quantum waveguide theory"
Delft University of Technology, The Netherlands"The Kondo effect in quantum dots"‐35‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Aug. 18

Prof. Yoon-Ha Jeong

Aug. 28

Prof. Ramasamy
Dhanasekaran

Sept. 1

Prof. Klaus H. Ploog

Sept. 8Mr. Maarten R. Wegewijs

Sept. 8Dr. Martin N. Wybourne

Sept. 14

Prof. Uri Sivan

Oct. 10

Prof. Alexander Khaetskii

Oct. 10

Prof. Yshai Avishai

Oct. 11

Prof. Gerhard AbstreiterNov. 1

Prof. Gerrit E. W. Bauer

Nov. 7

Dr. Haiyan An

Pohang University of Science and Technology(POSTECH), Korea"Design considerations for SET integrated circuits:
power and manufacturability"
Anna University, Chennai, India"Thermodynamics and nucleation Studies of
AlGaN/GaN,
InGaN/GaN
andAlInN/GaN
heterosturctures"
Paul-Drude-Institute, Germany"Heteroepitaxy of highly mismatched systems androle of coincidence lattice"
Delft University of Technology, The Netherlands"Coherent transport of strongly correlated electrons
through three coherently coupled quantum dots"
Dartmouth College, USA"Single electron transport in metal nanoparticle
decorated biopolymers"
Technion-Israel Institute of Technology, Haifa, Israel"Self assembly of nanometer scale electronics bybiotechnology"
Institute of Microelectronics Technology, Russian
Academy of Sciences, Russia"Spin relaxation in semiconductor quantum dot"
Ben Gurion University, Israel"Kondo tunneling through real and artificial
molecules"
Technical University of Munich, Germany"Superlattice and quantum wire transistors
fabricated by cleaved edge overgrowth"
Delft University of Technology, The Netherlands"Semiclassicaltheoryofmesoscopic
magneto-electronics"
Hokkaido University"Spatial positioning control and optical properties ofself-assembled InAs quantum dots on GaAs
pyramids"

lV. Quantum Optics & Optical Materials
Date

Speaker

Affiliation"Topic"July 14

Dr. Peter Kuerz

July 28

Prof. Shun-Lien Chuang

Carl Zeiss, Germany"Optics for extreme ultraviolet lithography"
University of Illinois at Urbana-Champaign, USA"Strained quantum-well lasers: from static tohigh-speed modulation properties with injection
locking"‐36‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Oct. 4

Prof. Gareth Parry

Oct. 10

Dr. Tao Hong

Dec. 21

Dr. H. T. Grahn

Feb. 23

Prof. Zhigang Zhang

Imperial College, UK"Semiconductor optical micro-cavities for LEDs,
lasers, modulators and detectors"
Science University of Tokyo in Yamaguchi"Sound dark solitons in Bose-Einstein condensates"
Paul-Drude-Insitut, Germany"Spontaneous current oscillations and chaos in
weakly coupled superlattices"
Tianjin University, China"Pulse stretcher phase calculation and its applicationin chirped pulse amplifications"‐37‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Research Papers Published in International Journals (Fiscal 2000)
The number of research papers published in the international journals (English) in fiscal
2000 amounted to 163 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
QuantumElectron
ElectronPhysics
Physics
Quantum Optics &Quantum Optics &Optical Materials
Optical Materials
05

10 15 20 25 30 35 40 45 50 55 60 65 70
Number of Papers

The major journals and the number of published papers are shown below.
General Science Journals
Name（IF99）*

NumberNatureScience（29.491）（24.595）

3
1

Specialized Journals
Name（IF99）*

NumberJapanese Journal of Applied Physics
Physical Review B
Applied Physics Letters
Physical Review Letters
Journal of Applied Physics
Journal of the Physical Society of Japan
Journal of American Chemical Society
Physical Review A
Macromolecules
IEEE Electron Device Letters
Advanced Materials
Analytical Chemistry
Optics Letters（1.411）（3.008）（4.184）（6.095）（2.275）（2.083）（5.537）（2.639）（3.534）（3.018）（5.415）（4.555）（3.537）

31
18
15
7
5
4
3
3
2
2
1
1
1

＊ IF99 : Impact factor 1999（Journal Citation Reports, 1999）

The average impact factor for individual research papers from all NTT Basic ResearchLaboratories is 2.96.

‐38‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

Presentations at International Conferences (Fiscal 2000)
The number of the presentations at the international conferences in fiscal 2000 amounted
to 231 in Basic Research Laboratories as a whole. The number of presentations according totheir research areas is as follows.

Research Areas

Device Physics

Materials Science
QuantumElectron
Electron
Quantum
Physics
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

NumberInternational Symposium on Carrier Interaction in Mesoscopic Systems 2001
25th International Conference on the Physics of Semiconductor
2000 Fall Meeting of Materials Research Society
2001 Spring Meeting of American Physical Society
2000 International Workshop on Nitride Semiconductors

22
19
9
9
8

The 2000 International Chemical Congress of Pacific Basin Societies
14th International Conference on High Magnetic Fields in Semiconductors

6
5

47th International Symposium of the American Vacuum Society
4th International Workshop on Quantum Functional Devices
10th International Conference of Metal Organic Vapor Phase Epitaxy

5
4
4

The 7th International Workshop on Femtosecond Technology
13th International Conference on Crystal Growth

43

12th International Symposium on Chirality 2000
2000 International Electron Device Meeting

3
2

‐39‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)

List of Invited Talks at International Conferences (Fiscal 2000)

I. Device Physics(1) H. Hibino and T. Ogino, "Si twinning superlattice: Growth of new single crystal Si",
US-Japan seminar on Mesoscopic Phenomena on Surfaces, Park City, USA (April,
2000).
(2) Y. Takahashi, A. Fujiwara, Y. Ono, and K. Murase, "Silicon single-electron devices andtheir applications", The 30th IEEE International Symposium on Multiple-Valued Logic(ISMVL), Portland, USA (May, 2000).
(3) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi, D.
Bottomley, and Zhaohui Zhang, "Control of atomic structures on Si surfaces for
wafer-scale nanointegration", International Symposium on Advanced Science andTechnology of Si Materials, Kona, USA (November, 2000).
(4) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi, D.
Bottomley, and Zhaohui Zhang, "Control of Si surface for quantum-dot network devices",
4th International Workshop on Quantum Functional Devices (QFD2000), Kanazawa,
Japan (November, 2000).
(5) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi, andZhaohui Zhang, "Bottom-up approach for nanointegration", Nanoarchitectonics Using
Suprainteraction (NASI1), Tsukuba, Japan (November, 2000).
(6) Y. Watanabe, S. Suzuki, F. Maeda, and T. Kiyokura, "Synchrotoron radiation
photoelectron spectroscopy of nanostructures", 1st. International Workshop on
Nano-scale Spectroscopy, Trieste, Italy (December, 2000).
(7) T. Ito, K. Shiraishi, and A. Taguchi, "Quantum mechanical approach for understanding
the growth process of semiconductors", The 2000 International Chemical Congress ofPacific Basin Societies (Pacifichem2000), Honolulu, USA (December, 2000).
(8) Y. Takahashi, Y. Ono, A. Fujiwara, and K. Murase, "Advanced technologies for Si-based
single-electron tunneling devices", International Symposium on Formation, Physics andDevice Application of Quantum Dot Structures (QDS2000), Sapporo, Japan (September,2000).
(9) K. Shiraishi, H. Kageshima, and S. Uematsu, "Microscopic mechanism of Si oxidation",
25th International Conference on the Physics of Semiconductors, Osaka, Japan(September, 2000).
(10) Y. Homma, "Surface imaging by ultrahigh vacuum scanning electron microscopy”, 2nd
LEEM/PEEM Workshop, Paris, France (September, 2000).

‐40‐

Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)(11) Y. Takahashi, A. Fujiwara, Y. Ono, S. Horiguchi, K. Shiraishi, M. Nagase, K. Murase,"Advanced techniques for silicon single-electron devices", International Conference on
Experimental Implementation of Quantum Computation (IQC01), Sydney, Australia(January, 2001).
(12) P. Kuniyil and T. Ogino, "Fabrication of functional nanostructures on silicon throughchemical bond manipulation", Science and Technology of Nanostructured Materials,
Institute of Physics, Puri, India (January, 2001).
(13) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, H. Omi, D.
Bottomley, and Zhaohui Zhang, "Si surface design for nanostructure self-assembly",
Symposium on Surface Science, 2001 (3S'01), Furano, Japan (January, 2001).
(14) H. Hibino and T. Ogino, "Growth of Si twinning superlattice", Lawrence Symposium on
Critical Issues in Expitaxy, Scottsdale, USA (January, 2001).
(15) K. Shiraishi, N. Oyama, K. Okajima, N. Miyagishima, K. Takeda, H. Yamaguchi, T. Ito,and T. Ohno, "Plastic versus elastic strain relaxation in heteroepitaxy of InAs/GaAs(110)",
Ringberg Workshop, Rottach-Egern, Germany (February, 2001).
(16) Y. Takahashi, A. Fujiwara, Y. Ono, S. Horiguchi, K. Shiraishi, M. Nagase, and K.
Murase, "Silicon single-electron transistor", 2001 March Meeting of the American
Physical Society, Seattle, USA (March, 2001).
(17) T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, P. Kuniyil, K. Sumitomo, D. Bottomley,and Zhaohui Zhang, "Self-assembly process for quantum structures on Si wafers", 6thInternational Symposium on Advanced Physics Field-Growth of Well-Defined
Nanostructures (APF-6), Tsukuba, Japan (March, 2001).
(18) H. Hibino and T. Ogino, "Epitaxial growth of Si twinnig superlattice", 6th International
Symposium on Advanced Physics Field-Growth of Well-Defined Nanostructures(APF-6), Tsukuba, Japan (March, 2001).

II. Materials Science(1) M. Naito, S. Karimoto, and H. Yamamoto, "New superconducting lead cuprates preparedby molecular beam epitaxy", The 4th Conference on Superconducting and Related
Oxides: Physics and Nanoengineering, Orland, USA (April, 2000).
(2) H. Sato, A. Tsukada, M. Naito, and A. Matsuda, "La-214 thin films under epitaxial
strain", 2000 International Workshop on Superconductivity (ISTEC), Matsue, Japan(June, 2000).
(3) M. Notomi, "Light propagation control in phtonic crystals", International Workshop on
Femtosecond Technology (FST2000), Tsukuba, Japan (June, 2000).

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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)(4) K. Ajito and K. Torimitsu, "Spectroscopy of organic and biological single particles on
nanometer and micrometer scales using a near-infrared laser Raman trapping system",
The 2000 Meeting of the International Union of Microbeam Analysis Societies(IUMAS2000), Hawaii, USA (July, 2000).
(5) H. Shibata, "Double Josephson plasma in SmLa1-xSrxCuO4-d single crystal", 2ndInternational Symposium of Intrinsic Josephson Effects and Plasma Oscillations in
High-Tc Superconductors (Plasma2000), Sendai, Japan (August, 2000).
(6) H. Sato, M. Naito, A. Tsukada, S. Karimoto, and A. Matsuda, "Influence of substrates on
epitaxial thin films of high-temperature superconductors", 2nd International Symposiumof Intrinsic Josephson Effects and Plasma Oscillations in High-Tc Superconductors(Plasma2000), Sendai, Japan (August, 2000).
(7) T. Suemitsu, T. Ishii, and Y. Ishii, "Gate and recess engineering for ultrahigh-speed
InP-based HEMTs", 2000 Topical Workshop on Heterostructure Microelectronics
Information System Applications (TWHM'00), Kyoto, Japan (August, 2000).
(8) J. Nitta, C. M. Hu, A. Jensen, J. B. Hansen, and H. Takayanagi, "Spin injection anddetection experiment with multiple NiFe/InAs/NiFe junctions", The International
Conference on the Physics and Application of Spin-related Phenomena in
Semiconductors (PASPS 2000), Sendai, Japan (September, 2000).
(9) M. Fujiki, "Experimental test for a left-right asymmetry of helical polymers",
International Symposium on Chirality (Chirality2000), Shamonix, France (September,2000).
(10) T. Watanabe, T. Fujii, and A. Matsuda, "Growth of Bi2Sr2Ca2Cu3O10+δ single crystals by
I-TSFZ method", 6th International Workshop on Chemical Designing and Processing ofHigh-Tc Superconductors (Chem-HTSC-VI), Tokyo, Japan (October, 2000).
(11) Y. Y. Suzuki, "Ribbon polymers and polymers at surfaces", Soft Condensed Matter:
Physical and Biological Aspects, Canberra, Australia (October, 2000).
(12) H. Tamura, K. Shiraishi, T. Kimura, and H. Takayanagi, "Artificial crystals designed insemiconductor dot arrays", 4th International Workshop on Quantum Functional Devices(QFD2000), Kanazawa, Japan (November, 2000).
(13) T. Ishii, A. Yokoo, T. Tamamura, and K. Shigeharam, "Fulleren nanocomposite resist fornanolithography", The 2000 Fall Meeting of the Material Research Society (MRS2000
Fall Meeting), Boston, USA (November, 2000).
(14) A. Yokoo, M. Nakao, H. Masuda, and T. Tamamura, "Direct nanoprinting technology
and its application of nanostructure fabrication", IEEE Lasers and Electro-Optics Society
2000 Annual Meeting (LEOS 2000), Rio Grande, Puerto Rico (November, 2000).
(15) J. Temmyo, H. Kamada, H. Ando, and T. Tamamura, “Semiconductor nanostructures via
self-organization for a two-level system”, The 10th Seoul International Symposium on
the Physics of Semiconductors and Applications-2000 (ISPSA-2000), Cheju Island,
Korea (November, 2000).
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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)(16) H. Takayanagi，H. Tamura, and K. Shiraishi, "Artificial crystals in semiconductor
quantum-dot array”, COE International Symposium, Shonan, Japan (December, 2000).
(17) H. Takayanagi，H. Tamura，K. Shiraishi, and T. Kimura, "Design of a semiconductor
ferromagnet in artificial crystals", XXXVIth Rencontres de Moriond, Les Arcs, France(January, 2001).
(18) M. Notomi, "Negative refractive optics in photonic crystals”, Photonics West 2001, San
Jose, USA (January, 2001).
(19) H. Nakashima, M. Fujiki, K. Torimitsu, and M. Motonaga, "Switchable induced circulardichroism of chiral aggregates of poly (alkylalkoxyphenylsilane) bearing remote chiralgroups", International Symposium on Silicon-Containing Polymers and Applications(ISPA), Ebina, Japan (February, 2001).

III. Quantum Electron Physics(1) N. Maeda, T. Saitoh, K. Tsubaki, T. Nishida, and N. Kobayashi, "Two-dimensional
electron gas transport properties in AlGaN/GaN single- and double-heterostructure
field-effect transistors", European Materials Research Society Spring Meeting (EMRS2000 Spring Meeting), Strasbourg, France (May and June, 2000).
(2) Y. Hirayama, "Carrier interaction in semiconductors: toward quantum computing",
International Workshop on Spintronics and Quantum Computing, Tokyo, Japan (September, 2000).
(3) T. Fujisawa, "Energy relaxation processes in quantum dots", The 4th International
Conference on High Magnetic Fields in Semiconductors (SemiMag-2000), Matsue, Japan(September, 2000).
(4) K. Kanisawa, M. J. Butcher, H. Yamaguchi, and Y. Hirayama, "Imaging of Friedel
oscillations at epitaxially grown InAs(111)A surfaces using scanning tunnelingmicroscopy", 25th International Conference on the Physics and Semiconductors (ICPS25),
Osaka, Japan (October, 2000).
(5) D. G. Austing, Y. Tokura, H. Tamura, S. Sasaki, S. Amaha, K. Ono, and S. Tarucha,"Vertical quantum dot artificial molecules", International Workshop on Artificial Atoms
and Related Finite Fermion and Boson Systems, Trento, Italy (October, 2000).
(6) T. Matsuoka, "Impact on InGaAlN growth of substrate and polarity effects", Next
Generation mm-Wave Solid State Power: Materials, Devices & Systems Workshop,
South Padre Island, USA (October, 2000).
(7) T. Fujisawa, "Transient current spectroscopy of quantum dots", International Symposiumon Quantum Functional Devices, Kanazawa, Japan (November, 2000).
(8) T. Makimoto, K. Kumakura, and N. Kobayashi, "p-InGaN/GaN heterojunction diodes andtheir application to heterojunction bipolar transistors", Materials Research Society 2000
Fall Meeting (MRS2000 Fall Meeting), Boston, USA (November and December, 2000).
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Research Activities in NTT Basic Research Laboratories Vol. 11 (August, 2001)(9) Y. Hirayama, K. Kanisawa, and T. Fujisawa, "Temporal and spatial characterization ofsemiconductor quantum dots", 1st International Conference on Experimental
Implementation of Quantum Computation (IQC01), Sydney, Australia (January, 2001).
(10) T. Fujisawa, "Time-dependent tunneling spectroscopy of single and double quantum dot
in the Coulomb blockade regime", 2001 International Seminar on Advanced
Semiconductor Device and Circuits, Sapporo, Japan (January and February, 2001).
(11) M. Kasu and N. Kobayashi, "MOVPE growth and large field emission of heavily
Si-doped AlN", 6th Japan-Taiwan seminar of science and technology, Chiba, Japan(February, 2001).
(12) Y. Hirayama, K. Muraki, A. Kawaharazuka, K. Hashimoto, and T. Saku, "Backgatedlayers and nano structures", Advanced Research Workshop on Semiconductor
Nanostructures (ARW2001), Queenstown, Australia (February, 2001).
(13) D. G Austing, T. Tokura, S. Tarucha, P. Matagne, and J. P. Leburton, "Addition energy
spectrum of a quantum dot disk up to third shell", Advanced Research Workshop on
Semiconductor Nanostructures (ARW2001), Queenstown, Australia (February, 2001).

IV. Quantum Optics & Optical Materials(1) H. Nakano, T. Nishikawa, N. Uesugi, J. Limpouch, and A. A. Andreev, "Femtosecond
laser-produced plasma as x-ray sources", XXVI European Conference on Laser
Interaction with Matter (ICXRL 2000), Prague, Czechoslovakia (June, 2000).
(2) H. Nakano, P. Lu, T. Nishikawa, and N. Uesugi, "X-ray short pulse generation fromfemtosecond laser-produced plasma and its application in pump-probe spectroscopy",
10th Conference on Laser Optics (LO' 2000), St. Petersburg, Russia (June, 2000).
(3) T. Nishikawa, H. Nakano, and N. Uesugi, "Efficient generation of ultrashort x-ray pulses
form femtosecond laser-produced plasma toward time-resolved x-ray spectroscopy", The
7th International Workshop on Femtosecond Technology (FST2000), Makuhari, Japan(June, 2000).
(4) N. Uesugi, H. Nakano, T. Nishikawa, and P. Lu, "Efficient soft x-ray generation fromfemtosecond-laser-produced plasma and its application to time resolved spectroscopy",
7th International Conference on X-ray Lasers (ICSRL 2000), Saint-Malo, France (July,
2000).
(5) H. Nakano, T. Nishikawa, and N. Uesugi, "Efficient soft x-ray pulse generation fromfemtosecond-laser-produced plasma and its application to time-resolved spectroscopy",
6th Conference on Optics (ROMOPTO2000), Bucharest, Rumania (September, 2000).

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Editorial Committee
Hiroshi Inokawa
Kazuaki Furukawa
Narihiko Maeda
Hiroyuki Kageshima

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