DRAFT – HTE Site Reports - DRAFT
Site:
Advanced Technology Research Laboratories
Technical Development Bureau
Nippon Steel Corporation
3-35-1 Ida, Nakahara-Ku,
Kawasaki 211-0035, Japan
Tel: (81) 447 97 1254 Fax: (81) 447 52 6349
Date Visited:
11 June 1998
TTEC Attendees:
M. S. Shur (report author), R. C. Clarke, V. Dmitriev, U. Varshney
Hosts:
Dr. Naoki Okumura, Director
Dr. Misao Hashimoto, Senior Manager, Planning
Mr. Toshiki Hino, Senior Manager, Planning
Mr. Hirokatsu Yashiro, Senior Researcher
5-10-1 Fuchinobe, Sagamihara, Kanagawa 229-8551 Japan
Dr. Noboru Ohtani, Senior Researcher
5-10-1 Fuchinome, Sagamihara, Kanagawa 229-8551 Japan
Dr. Masatoshi Kanaya, Senior Researcher
5-10-1 Fuchinome, Sagamihara, Kanagawa 229-8551 Japan
1
OVERVIEW OF ADVANCED TECHNOLOGY RESEARCH LABORATORIES
Nippon Steel had sales of over ¥2 trillion in 1996 worldwide. In 1987, the corporation launched an effort in
new materials, electronics, information, and communication technology, which is supported in part by its
Advanced Technology Research Laboratories. This laboratory is one of 3 laboratories of the Technical
Development Bureau of Nippon Steel. The electronic products associated with the Advanced Technology
Research Laboratories include the following:


electronics materials

300-mm (12-inch) Si wafers

200-mm and 150-mm SIMOX wafers

25-mm (1-inch) SiC wafers (with 2-inch wafers under development)
circuit design products

60-micron fine-pitch bonding with 22-micron gold bonding wire

40-micron micro ball bumps for high density LSI packaging
The laboratory employs 130 researchers. The research directions also include advanced materials design
using computations, development of new glass/plastic materials (flexible glass), and new materials
characterization techniques based on positron annihilation and X-ray characterization methods.
SiC PROGRAM AT ADVANCED TECHNOLOGY RESEARCH LABORATORIES
Nippon Steel produces SiC substrates grown by modified Lely method. (Several other Japanese companies
might be developing SiC bulk and epitaxial growth capabilities.) Nippon Steel has shown interest in
expanding its SiC program to include epitaxial growth of SiC and, possibly, of GaN-based materials. Plans
are underway to develop 2-inch SiC bulk technology and (in a more distant future) 3-inch bulk SiC
technology.
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Most SiC work has been funded internally. However, Nippon Steel is one of the participants in the NEDOfunded National Project on Combustion Control Systems for Conservation.
The SiC substrates are doped n or p type by N and B, respectively. The doping range is from 1x10 17 cm-3 to
3x1018 cm-3. The wafer resistivity varies from less than 10 -2 ohm cm (for n-type wafers) to more than 1000
ohm cm for p-type wafers. Breakdown voltages over 1,000 V have been demonstrated for 2x10 16 cm-2
material.
Typical surface roughness is 1.3 nm to 1.8 nm. Dislocation density is on the order of 10 4 – 105 cm-2. The
price is ¥125,000 for a 1-inch SiC wafer.
The biggest market seen in the short term is in substrates for blue GaN LEDs and laser diodes. In year 2000
and beyond, a larger market is expected in substrates for high temperature, high power electronics
components.
These are some of the examples of the Nippon Steel SiC research. Ohtani et al. (1998a) have studied
impurity incorporation kinetics during modified-Lely growth of SiC as a function of several growth
parameters. Results show that dynamic equilibrium is established between the vapor phase and the adsorbed
nitrogen. The polytype of the grown crystal and the seed orientation and face polarity affect the impurity
incorporation (Takahashi et al. 1995). The AFM studies reveal a noticeable difference in the growth
morphology between 6H-SiC (0001) and 4H-SiC (0001) .
Ohtani et al. has reported on the stepped structure on the {0001} facet plane of 6H-SiC. The height steps are
equal to 1.5 nm (Ohtani 1998b).
This group has also reported on a dramatic reduction of the micropipe density (as revealed by KOH etch)
from 1,000 to 10 cm-2 (Ohtani et al. 1998c).
By optimizing growth conditions, the Nippon Steel group has obtained 6H-SiC and 4H-SiC samples with
resistivities as low as 7x10-3 cm and 5.37x10-3 cm, respectively (Onoue et al. 1996).
SiC crystals have been also grown in [1100] and [1120] directions (Takahashi et al. 1997).
All in all, Nippon Steel has one of the strongest SiC programs in Japan.
REFERENCES
Ohtani, N., J. Takahashi, M. Katsuno, H. Yashiro, and M. Kanaya. 1998c. The Transactions of the Institute of
Electronics, Information and Communication Engineers. C-II (J81, No. 1):112-121.
Ohtani, N., M. Katsuno, J. Takahashi, H. Yashiro, and M. Kanaya. 1998a. J. Appl. Phys. 83 (8):4486.
Ohtani, N., M. Katsuno, J. Takahashi, Y. Yashiro, and M. Kanaya. 1998b. Surface Science. 398:L303.
Onoue, K., T. Nishikawa, M. Katsuno, N. Ohtani, H. Yashiro, and M. Kanaya. Jpn. Appl. Phys. Part I (4a):2240.
Takahashi, J., N. Ohtani, M. Katsuno and S. Shinoyama. 1997. J. Crystal Growth. 181:229.
Takahashi, J., N. Ohtani, and M. Kanaya. 1995. Jpn. J. Appl. Phys. 34, Part 1 (9a):4694.
DRAFT – HTE Site Reports - DRAFT
Site:
Central Research Laboratories
Matsushita Electric Industrial Co., Ltd.
3-4 Hikaridai, Seika, Soraku,
Kyoto 619-0237, Japan
Tel: (07) 74 98 2511 Fax: (07) 74 98 2585
Date Visited:
9 June 1998
TTEC Attendees:
M. S. Shur (report author), R. C. Clarke, V. Dmitriev, U. Varshney
Hosts:
Dr. Makoto Kitabatake
Dr. Eng. Kunimasa Takahashi
Mr. Toshiyuki Maeda, Senior Research Engineer
Mr. Masao Uchida
3
OVERVIEW OF CENTRAL RESEARCH LABORATORIES
The facility is a new $140 million building occupied by 250 researchers and supporting staff. Matsushita has
sales of $79 billion per year and 265,397 employees worldwide. The company spends over $4 billion on
research and development. The research areas of the Central Research Laboratories include the following:




advanced science

functional mechanisms of biological molecular machines

human interface

intelligent electronics
materials

nanostructure controlled materials

magnetic, piezoelectric, and dielectric materials

superconductive materials

nanoscale fine milling technology
thin films

low cost and large area films

dielectric thin films

diamond and SiC thin films (“new diamond”)
devices

light modulators

quantum devices

high efficiency light emitters

blue semiconductor lasers
In 1996, the scientists of the Central Research Laboratories published 133 papers in Japan and 45 papers
overseas. They also filed 33 overseas patents and a much larger number of patents in Japan.
NEW DIAMOND GROUP
The prime area of interest of the group is in materials research on CVD diamond and SiC films. The research
is company funded. However, a $4 million per year, 6-year funding from NEDO has been shared among 5
companies and some universities for combustion control systems for energy conservation. The project will
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be continued for another year. The device applications are primarily the responsibility of the Matsushita
Electronic Corporation Research Laboratory.
Dr. Kitabatake is an expert in growth simulation techniques (Kitabatake 1997). Most of his effort seems to
be centered on 3C-SiC heteroepitaxial growth on Si and related problems of surface reconstruction. NEDO
has supported the work.
He also reported on the growth of 3C-SiC CVD/MBE films (Uchida et al. 1998).
Molecular dynamics simulations have been conducted with the University of Illinois group (Kitabatake and
Greene 1996).
Another project involves CVD diamond growth. Deguchi et al. (1997) have reported on piezoelectric
properties of polycrystalline p-type diamond CVD films doped by boron. This work has been a joint
research effort with the Osaka University group. The deposition conditions are as follows:

gas source
CO/H2/B2H6

total gas flow
110 sccm

CO/H2 ratio
1.85%

pressure
4,000 Pa

microwave power
300 W

substrate temperature
900oC
The p-type films are about 2 microns thick and are grown on insulating polycrystalline diamond substrates.
Piezoresistors have 500-micron x 50-micron dimensions and have shown gauge factors of 1000 and 700 at
room temperature and at 200oC, respectively. This compares with a gauge factor of 150 for p-type Si films.
The group is also involved in research on UV detectors for combustion control.
REFERENCES
Deguchi, M., N. Hasa, M. Katabatake, H. Lotera, S. Shima, and M. Kitagawa. 1997. Diamond and related materials.
6:367-373.
Kitabatake, M. 1997. Phys. Status Sol. (b):202, 405.
Kitabatake. M. and J. E. Greene. 1996. Appl. Phys. Lett. 14:2048.
Uchida, M., M. Deguchi, K. Takahasi, M. Kitabatake, and M. Kitagawa. 1998. Materials Science Forum. 264-268:243246.
DRAFT – HTE Site Reports - DRAFT
5
Site:
Electrotechnical Laboratory (ETL)
Agency of Industrial Science and Technology (AIST)
Ministry of International Trade and Industry (MITI)
1-1-4 Umezono, Tsukuba
Ibaraki 305-868, Japan
Tel: (81) 298 54 5243 Fax: (81) 298 54 5403
Date Visited:
10 June 1998
TTEC Attendees:
P. M. Stipan (report author), T. P. Chow, S. DenBaars, C. Uyehara
Hosts:
Dr. Kazuo Arai, Director, Materials Science Division, ETL
Dr. Hideyo Okushi, Assistant Director, Materials Science Division
Dr. Sadafumi Yoshida, Leader, Wide Bandgap Semiconductor Lab., Materials Science
Division.
Dr. Hajime Okumura, Senior Researcher, Wide Bandgap Semiconductor Lab.,
Materials Science Division.
Dr. Shiro Hara, Interface Science on Semiconductors Group, Materials Science
Division
Dr. Naoto Kobayashi, Director, Quantum Radiation Division
Dr. Toshihiro Sekigawa, Electron Devices Division
INTRODUCTION
Researchers at the Electrotechnical Lab (ETL) believe an expansion of electronics is possible through the
development of “hard electronics,” otherwise known as electronics based on wide bandgap semiconductors.
A long-term project has started investigating 3 materials primarily: silicon carbide, nitrides, and diamond.
ETL could not state the project details but did discuss the project stages, timeline, initial budget, and number
of companies and universities wishing to join this project.
Presentations included ETL work on metal electrodes, SiC interfaces, hot ion implants, III-nitrides, and
diamond films. ETL provided many paper reprints.
When asked about packaging concerns for these materials, Dr. Kazuo Arai commented, “One cannot make
dinner when still preparing the plates – but this activity is very important and will be included in the next
stage of the project (in 5 to 8 years).”
STATUS OF ACTIVITIES
ETL’s own Dr. Arai is responsible for the “Hard Electronics” project sponsored by the Japanese government.
He provided Figure ETL.1, which shows pictorially the application demands and the required specifications
driving this project.
He believes that SiC is the material front-runner, but ETL will include the development of nitride and
diamond. Substrate processing is key because of crystal growth defects, micropipe dislocations, and
sublimation. Channel resistance issues and electrode issues are also being addressed using substrate
processing. For example, he discussed FET enhancements, including JFET (ion implantation), MOSFET
(gate oxide), and MESFET (ohmic contact).
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Fig. ETL.1. Expansion of Electronics by the Development of Hard Electronics.
The project target has 3 stages:
1.
develop fundamental devices (1998-2003)
2.
develop innovative devices with special purposes (2003-2007)
3.
create innovation in various systems (by 2010)
Stage 1 research may divide into two groups:
1.
research fundamental devices with new substrates and new processing
2.
research fundamental devices by using available processing techniques
This project started in October 1998 with its half-year budget set at ¥320 million and an anticipated project
budget set at nearly ¥7.5 billion. Presently 10 companies wish to join. Six to 8 universities collaborate with
ETL, but the exact number depends on the budget.
LPCVD
ETL researchers have found that LPCVD improves the quality of 3C-SiC epilayers on Si with atomically
smooth surfaces as compared to APCVD. They plan to demonstrate the quality by fabricating a Schottky
device. They use LPCVD-grown 3C-SiC epilayers as the substrates for the growth of cubic III-nitrides.
SiC Interfaces
Dr. Shiro Hara presented SiC interfaces and metal electrodes for 6H-SiC (0001). A graph showed the
Schottky barrier height versus metal work function for titanium, molybdenum, and nickel. A 5% HF etch is
used for cleaning along with boiling water (new process with oxygen dissolved in pure water). This lowers
the contact resistivity.
Hot Ion Implant
Dr. Kobayashi presented information on hot ion implant. For 2-3 years ETL has focused on SiC process and
conduction control (device processes). He said that it is difficult for proper p-types (use Al or B) in SiC, but
the n-type is easier and N2 is appropriate. Aluminum sublimation occurs in a high dose implant. He
discussed Poisson annihilation for defect control and stated that no implant has been used at ETL for GaN.
DRAFT – HTE Site Reports - DRAFT
7
III-Nitrides
ETL grows crystals by Molecular Beam Epitaxy (MBE), but this technique has not been the best. ETL uses a
new plasma to improve the growth rate. It uses surface science for hexagonal epilayers on sapphire and
cubic layers on GaAs and 3C-SiC. The optical properties of cubic III-nitrides are used for characterization.
The h-GaN (hexagonal-GaN) is 0.2eV larger than the c-GaN (cubic-GaN). The future plan is to evaluate the
function of III-nitride heterostructures, wide bandgap materials with large band offset, large saturation drift
velocity, a small dielectric constant, and chemical and thermal stability.
Diamond Films
High pressure and high temperature synthesize diamonds. Impurity problems over large areas are a concern.
The two methods ETL evaluated for epi (crystalline) are hetero-epi growth and homo-epi growth. ETL has
found that homo-epi growth produces a high quality, atomically flat film. For clean epitaxy, ETL researchers
recommend the following:

Keep plasma away from the chamber wall to reduce bombardment

Use a very low base pressure

Use independent control of substrate temperature and plasma power
ETL presented dependence of CH4 concentration (CH4 /H2). It compared concentration percentages at 6
hours’ deposition time from 0.05%, 0.15%, 0.3%, 0.5%, 1% (defect loaded), and 2.0%. At 0.05%, the
homogeneous material is clean. Going to 0.025% reveals an atomic force image of a 200-nm x 200-nm film
with an atomically flat surface in the whole region of the substrate–but this process takes 42 hours’
deposition time.
ETL showed current density versus voltage curves for an Al/diamond (001) Schottky barrier diode with b =
1.58eV.
For a B-doped CVD diamond (using B[CH3]3), ETL presented the temperature dependence of Hall mobility
compared to natural diamond.
REFERENCES
Arai, K. et al. 1997. Prospect of hard electronics: what and how approach. (paper). Oct .
Balakrishnan, K., et al. 1997. Structural analysis of cubic GaN through X-ray pole figure generation. (paper). October.
Balakrishnan, K., et al. 1998. Study on the initial stages of heteroepitaxial growth of hexagonal GaN on sapphire by
plasma assisted MBE. (paper). March.
Feuillet, G., et al. 1997. Surface reconstructions and III-V stoichiometry: the case of cubic and hexagonal GaN. (paper).
Feuillet, G., et al. 1997. Arsenic mediated reconstructions on cubic (001) GaN. Feb.
Hara, S., et al. 1997. Control of Schottky and ohmic interfaces by unpinning Fermi level. (paper).
Ishida, Y. et al. 1997. Atomically flat 3C-SiC epilayers by low pressure chemical vapor deposition. (paper).
Ishida, Y. et al. CVD growth mechanism of 3C-SiC on Si substrates. (paper).
Kobayashi, N., et al. 1997. Ion-beam-induced epitaxial crystallization (IBIEC) and solid phase epitaxial growth (SPEG)
of Si1-xCx layers in Si fabricated by C-ion implantation. (paper).
Okumura, H. 1998. Arsenic surfactant effects and arsenic mediated molecular beam epitaxial growth for cubic GaN.
(paper). June.
Okumura, H. et al. 1994. Epitaxial growth of cubic and hexagonal GaN by gas source molecular beam epitaxy using a
microwave plasma nitrogen source. (paper).
Okumura, H. et al. 1997. Growth and characterization of cubic GaN. (paper).
Okumura, H., et al. 1997. Bandgap energy of cubic GaN. (paper).
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Okumura, H., et al. 1998. Analysis of MBE growth mode for GaN epilayers by RHEED. (paper). March.
Okumura, H., et al. 1998. Growth of cubic III-nitrides by gas source MBE using atomic nitrogen plasma: GaN, AlGaN
and AlN. (March)
Reddy, C., et al. The origin of persistent photoconductivity and its relationship with yellow luminescence in molecular
beam epitaxy grown undoped GaN. (to be published in APL).
Takahashi, T., et al. Surface morphology of 3C-SiC heteroepitaxial layers grown by LPCVD on Si substrates. (paper).
Tanaka, Y., et al. Hot implantation of Ga+ ion in SiC. (paper). Dec.
Teraji, T., et al. 1997. Ideal ohmic contact to n-type 6H-SiC by reduction of Schottky barrier height. (paper). May.
DRAFT – HTE Site Reports - DRAFT
Site:
Furukawa Electric Co., Ltd.
Yokohama Research & Development Laboratories
4-3 Okano 2-chome, Nishi-ku, Yokohama
Kanagawa Prefecture 220, Japan
Tel: (81) 453 11 1219 Fax: (81) 453 16 6374
Date Visited:
9 June 1998
TTEC Attendees:
T. P. Chow (report author), S. DenBaars, P. M. Stipan, C. Uyehara
Hosts:
Dr. S. Yoshida
Dr. J. Suzuki
9
INTRODUCTION
The Furukawa Electric Co. Ltd. was founded in 1884 and reorganized in 1920. Its present sales amount to
¥56.6 billion (approximately $400 million), and it has 10,000 employees. Its major business activities
include many industrial and consumer products, such as electric and magnetic, superconducting and optical
fiber cables, automotive parts and accessories, metal alloys, electronic and optical materials, components and
system products. Its R&D activities can be divided into 5 categories:
1.
information systems centering on optical technology
2.
electronics exploration progressing rapidly into even wider ranges of applications
3.
new materials and functions
4.
energy studies to support the foundations of industrial development
5.
advanced automotive electric equipment and parts
The Yokohama R&D Laboratories is one of Furukawa’s 7 research laboratories and has been at its present
location since 1987. The lab has about 300 employees and occupies a total land area of 22,000 m2.
STATUS OF ACTIVITIES
Furukawa Electric is a subsidiary of the Furukawa group, which also includes the Fuji Electric and Fujitsu.
Fuji Electric is a major supplier of silicon power device modules, and Fujitsu is a major computer and
integrated circuit company. Furukawa’s products include many industrial and consumer products, like
superconducting cables, memory alloys, optical devices and modulators. Four engineers, including Dr.
Yoshida, discussed the technical details of the program and answered most of the TTEC panel’s inquiries.
Furukawa is interested in both GaN and SiC.
Furukawa has been conducting epitaxial growth of GaN on sapphire substrates since 1986 using gas source
MBE. One reason for using MBE as the growth method is that Furukawa had already been using GaAs MBE
for many years. Furukawa’s interests in GaN include optical laser diodes as well as high frequency, high
voltage power devices. Additionally, it would like to serve as a GaN epi supplier to other companies (within
its group). It has a load-lock MBE system that utilizes DMHydrazine and NH 3 as precursors. Dr. Yoshida
and Dr. Suzuki commented that the growth of GaN on silicon is difficult because the film is under tension
and often cracks. Their growth experiments have been mostly done on 2-inch (0001) substrates. No growth
has been observed at temperatures below 800C with these precursors. A typical FWHM of 50 arcsec has
been measured, indicating very high quality epi layers. The FWHM is even sharper when undoped layers are
grown with a V/III precursor ratio increased by a factor of 3 and a substrate temperature of 850C.
Photoluminescence (PL) measurements of InGaN films with a 1% indium concentration indicate that the
commonly observed yellow band emission in GaN is absent. Mg-doped GaN films exhibit a sharp 430-nm
emission, but again an emission in the yellow wavelengths. Typical hole concentrations are in the 1-2x1017
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/cm3 range at room temperature. GaN was etched in ECR plasma with CH 4/Ar/H2 (15:7:5). Mg-doped films
are etched twice as slowly as undoped or Si-doped films. AlGaN films are etched at a 40% slower rate. A
selectivity of about 10 has been obtained over SiO2.
These process technologies have been employed to fabricate a lateral MESFET that is capable of
withstanding high temperatures. Pt-gate GaN MESFET with oxide passivation has been tested up to 500C.
After 500C annealing, a high gate-to-source leakage appears. Tungsten (with a small percentage of silicon)
has also been tried as the Schottky gate, but the device fails after 500C treatment. Schottky gate reliability
testing at 400C for 900 hours results in substantial degradation in gate-to-drain leakage. Ti/Al ohmic
contact stressing at 550C has shown no change in the abrupt interface. Besides MESFET, GaN MISFETs
with AlN as a gate insulator have been fabricated and yield BV larger than 100 V. A GaiV rpn bipolar
junction transistor has also been operated at 300°C.
REFERENCES
Detailed written comments to the TTEC HTE-Study Technical Issues.
Company profile and research laboratory brochures.
Yoshida, S. 1997. J. Appl. Phys. 81:1673.
Yoshida, S. 1998. J. Cryst. Growth. 191:278.
Yoshida, S., and J. Suzuki. 1998. Jpn. J. Appl. Phys. Lett. 37:L482.
Yoshida, S., and J. Suzuki. 1998. J. Appl. Phys. 84:2940.
DRAFT – HTE Site Reports - DRAFT
Site:
Institute of Space and Astronautical Science
Ministry of Education
3-1-1 Yoshinodai, Sagamihara
Kanagawa, Japan
Tel: (81) 427 59 8325 Fax: (81) 427 59 8463
Date Visited:
9 June 1998
TTEC Attendees:
T. P. Chow (report author), S. DenBaars, P. M. Stipan, C. Uyehara
Hosts:
Prof. Michio Tajima
Prof. Kazuyuki Hirose
11
INTRODUCTION
The Institute of Space and Astronautical Science (ISAS) belongs to the Ministry of Education. Its members
perform many research projects related to space exploration. Its mission is similar to that of the NASA Jet
Propulsion Laboratory of the United States.
The panelists met Prof. Tajima of ISAS in the Ministry of Education. Professor Tajima mentioned a national
project on low-loss power devices organized by ETL under Dr. Arai. Its focus is mainly SiC, and many
power device manufacturers support it. Since this project will be overseen by ETL, which the TTEC panel
would visit the next day, Prof. Tajima told the panel to seek the details while it was meeting Dr. Arai and his
colleagues at ETL. Prof. Tajima has organized many national conferences on high temperature electronics,
and he gave the panel the proceedings of all but one. He mentioned several Japanese companies working on
SiC that the panel was not visiting. These include Hoya, which makes 3C-SiC epi layers on Si substrates,
Hitachi, Fuji Electric, and Toshiba.
Prof. Tajima has given invited lectures on high temperature electronics applications. These include
geothermal probing and exploration of the inner planets and the sun. He introduced to us the background of
his laboratory by showing a 30-min video on space phenomena. Some of the highlights were the northern
lights and X-ray astronomy.
Prof. Tajima’s background is in semiconductor physics, particularly impurity and defect analysis, largediameter wafers, SOI wafers, GaAs, InP, and Si/Ge.
His previous material studies include
photoluminescence (PL) mapping of production-grade 6H- and 4H-SiC bulk and epitaxial wafers. By using
a microcomputer-controlled PL system, he and his colleagues have characterized p-type bulk and epitaxial
wafers and found a nonuniform distribution of unidentified deep levels on the wafer. Prof. Hirose, his
colleague present at the meeting, is an interfacial specialist on the SiO 2/Si system. There is no packaging
expert at ISAS. Prof. Tajima’s interests in high temperature electronics generally concern space exploration.
In particular, high temperature devices are needed for a Venus probe that will be dropped from an orbiting
satellite. Venus is covered with clouds of sulfuric acid, and the surface temperature is about 450C. The
temperature below the clouds, at an altitude of 20 km, is about 350°C. A balloon floating below the clouds
can explore the mystery of the 4-day rotation of Venus. A 5-kg probe will be used, and 1 kg would be saved
without the cooling system. The electronics need to be operating for 1-2 weeks.
The mission was one of the strongest potential project candidates planned for 1999, which would have been
an appropriate window for Venus. Unfortunately, the project was not accepted by ISAS, and the next target
launch has not been decided. Nevertheless, interest in the Venus mission is still very high, and feasibility
studies are underway.
Prof. Tajima indicated that due to budgetary uncertainties, he was not sure about the exact scope and nature
of the high temperature device activities that will take place at ISAS. The power level at which high
temperature devices will be considered is > 100 W. Characterizations of wide bandgap materials and siliconon-insulator are the main emphases. Besides the active devices, Prof. Tajima expressed concern about the
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temperature limitations (<200C) of passive components, such as capacitors. He mentioned Kyocera, a
company which develops high temperature ceramic packages in Japan. Also, he believes that the basic
parameters of the wide bandgap semiconductors are not known well enough, but ISAS will not determine
them. Prof. Tajima’s group will continue to collaborate with universities and industrial companies. He has
also proposed to perform device and material research in SiC.
The Japanese space market is much smaller than the U.S. market. A large number (>10) of Japanese
companies will participate in the National Project on Low-Loss Power Devices, but the expected SiC market
may be a small though important niche.
REFERENCES
Film on space exploration and ISAS.
Proceedings of most of the previous ISAS Research Meeting on High Temperature Electronics.
DRAFT – HTE Site Reports - DRAFT
Site:
Ion Engineering Institute Corporation
2-8-1, Tsuda-Yamate, Hirakata
Osaka 573-0128, Japan
Tel.: (81) 720 59 6651 Fax: (81) 720 59 6299
Date Visited:
10 June 1998
TTEC Attendees:
R. C. Clarke (report author), V. Dmitriev, M. S. Shur, U. Varshney, H. Morishita
Hosts:
Dr. Masanori Watanabe, Research Manager
Tomio Oyama, Research Manager
Yasuo Suzuki, Research Manager
Tomoaki Yoneda, 1st Project Research Lab
Tadao Toda, Chief Researcher, Sanyo Electric Co. Ltd.
Toshitake Nakata, President, SiC Semiconductors
2-52-1, Amanogahara-cho, Katano, Osaka, 576-034, Japan
13
INTRODUCTION
Its corporate literature states, “Ion Engineering Center Corp. (IECC) and Ion Engineering Institute
Corporation (IERIC) were established in 1998 in New Kansai science city in Japan. Main projects are
surface modification to improve corrosion and wear resistance of materials, high temperature SiC devices for
combustion control systems, refractory coatings on C/C composites, hardness enhancement for plastics, and
optosensors on the basis of inorganic and organic hetero-nano-systems. New challenges for microfabrication by ion implantation by using a vacuum arc evaporator and mimetic bio-materials synthesis with
biocompatibility are proposed.”
Professor Dmitriev gave a presentation of the status of SiC high temperature materials and electronics in the
United States. Mr. Chris Clarke discussed microwave power devices formed of SiC, and Professor Michael
Shur discussed the modeling and fabrication of GaN-based electronics.
RESULTS OF 1997 R&D ON COMBUSTION CONTROL SYSTEMS FOR ENERGY
CONSERVATION
Objectives and Content of R&D
Demand for more advanced and optimal combustion control systems has been growing, from the viewpoint
of both energy conservation and effective energy use. Realization of a control device operable at high
temperatures is needed. The objectives of this R&D are to develop basic technologies for realizing a silicon
carbide-based control device (hereinafter referred to as a “SiC device”) that would meet the above-mentioned
requirement, to manufacture the SiC device on a test basis, and to realize an energy-saving combustion
control system technology incorporating the SiC device. More specifically, to achieve an advanced and
optimal combustion control system, R&D is underway on the following basic technologies, with the aim of
realizing a SiC device operable in high temperature environments:

basic technology for manufacturing SiC wafer

basic technology for p-n conductivity control

basic technology for the SiC device

combustion control system technology
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THE OUTLINE OF 1997 R&D RESULTS
R&D on Basic Technology for SiC Device Fabrication
Crystallinity of commercially available SiC wafers has been characterized by X-ray topography.
Dislocations in SiC wafers exist randomly. The dislocation density is about 1x10 3~2x103/cm2, which is
about 100 times higher than that of an Acheson 6H-SiC crystal. In addition, SiC wafers are warped, and
radius of curvature for wafers is less than 18 m.
Ion Engineering Research Institute Corporation (IERI)
IERI has characterized the electric property of the thermal oxide layer by ion irradiation onto the Si face of
6H-SiC. The I-V characteristic indicates a high breakdown field and high resistivity of the oxide layer, and
the C-V characteristic and DLTS measurement indicate residual damage by ion irradiation near the interface
region of SiO2/SiC.
4H-SiC Schottky rectifiers with vanadium-implanted guard rings have been fabricated by using highly
resistive regions at the periphery of Schottky contacts. The reverse characteristics of 4H-SiC Schottky
rectifiers with guard rings improve in comparison with the rectifiers without guard rings. A maximum
breakdown voltage of 1630 V has been achieved. The breakdown field of the Schottky rectifier is very close
to the ideal value of 4H-SiC.
IERI has confirmed a p-type layer synthesis by Sc+ implantation into an n-type SiC layer. As the solubility of
Sc in SiC is very low, the annealing after Sc + implantation causes the out-diffusion of Sc to get away from
the surface of SiC. The C-V characteristic and SIMS measurement indicate that the electrical activation of
implanted Sc in SiC is around 50%.
Technical Development for SiC Single Crystalline Wafer Process
Nippon Steel Corporation (NSC)
NSC has examined the validity of Rutherford backscattering spectrometry (RBS) to characterize the
thickness of the damaged layer that should be removed in the final polishing process. Transmission electron
microscope (TEM) observations and thermal oxidation followed by HF dip reveal that the RBS estimation of
the thickness by the surface energy approximation is valid for relatively shallow damage (less than 70 nm).
However, RBS is rather limited for a thick, damaged layer. The recovery of the ratio of the aligned to the
random yields is favorable for the characterization of deep damage. RBS has proven to be a powerful tool,
capable of characterizing the thickness and crystallinity of a thin surface-damaged layer.
NSC has also studied the possibility of chemomechanical polishing technology in the final polishing process.
CMP technology for Si seems to be effective in reducing polishing induced damage. Although many
problems still remain to be solved, progress in CMP technology for SiC could lead to the realization of a
damage-free polishing technology in SiC wafer production.
The next subject in the slicing process has been to clarify problems for application to 2-inch crystals. Heavy
wear of the diamond blades has been observed in 2-inch wafer slicing. It is necessary to prevent the diamond
from wearing. More study should be undertaken.
R&D on SiC Sensor Devices
Matsushita Electrical Industrial Corporation
The HREELS measurement indicates that the 6H-SiC (0001) Si3x3 reconstruction is formed by additional
Si atoms that have one dangling bond each. Monohydridation of the 6H-SiC (0001) Si3x3 is achieved by
annealing it at 600C in a hydrogen atmosphere. Surface structure controls epitaxial growth, in which the
6H-SiC (0001) Si3x3 surface is at a temperature of 1050C. Heteroepitaxial CVD/MBE 3C-SiC films
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exhibit strong anisotropic electrical characteristics. Stacking faults observed with microtwins by TEM cause
the strong anisotropic characteristics of the heteroepitaxial CVD/MBE 3C-SiC.
R&D on High Temperature and High-Speed SiC Devices
Sanyo Electric Corporation (SEC)
SEC has conducted evaluations at high temperature on the prototype of a 6H-SiC MESFET with an Au-gate
and confirmed operation at temperatures as high as 400C. At high temperatures, both drain current and
transconductance (gm) values drop to half of that at room temperature. High temperature characteristics for
the Schottky gate diode indicate no significant reverse current leakage.
SEC has also developed a mesa-etching technology for the tapered structure of device edges in order to avoid
broken gate wires. Then it has sought to improve element characteristics by producing a 4H-SiC MESFET
prototype with a Pt-gate that diffuses very little Pt into the SiC at high temperature. As a result, SEC has
achieved a gm of 12.5 mS/mm, a pinch-off voltage of -7V, and a drain breakdown voltage of 140 V at room
temperature using an element with a channel length of 1 m, a channel width of 60 m x 2, a channel
thickness of 0.2 m, and a source drain distance of 4 m. SEC has also confirmed high temperature
operation at up to 400C for the 4H-SiC MESFET with a Pt-gate. Both the 6H- and 4H-SiC MESFETs
indicate hysteresis characteristics during both heating and cooling that are probably due to RIE-caused
changes in the SiC surface.
Finally, SEC has studied UV sensors, ion implanted nitrogen into p-type 6H-SiC as well as Al into n-type
6H-SiC. It has fabricated a narrow junction measuring just 0.2 m depth and confirmed diode characteristics
as part of an overall strategy aimed at integrating MESFETs and UV sensors.
Technical Developments on SiC Devices for Combustion System Control
Mitsubishi Electric Corporation
Mitsubishi has studied ion-implantation techniques for deep p-n junctions. It has implanted Al ions with a
high energy of 1.0-7.0 MeV onto a 4H-SiC substrate heated to 1000C for the first time. SIMS has been
used to examine a Al depth profile where the Al was implanted to the depth of 3 microns with a dose density
of 1.0 x 1019/cm3. RBS characterization indicates that the implantation causes irregularity of the SiC crystal.
The irregularity of the SiC implanted at 1000C decreases drastically compared to that obtained from room
temperature implants.
Mitsubishi also has studied ohmic n-type contact electrodes formed of Ni. The electrodes have been
deposited by electron-beam evaporation and annealed by rapid lamp annealing. Mitsubishi has also precisely
characterized the contact resistance using TLM. The contact resistances are ~1.0 x 10 -4cm2 and 4.0 x 10-5
cm2 for the carrier density of 8.0 x 1018/cm3 and 1.0 x 1019/cm3, respectively. The temperature of
annealing must be more than 960C to reduce contact resistance.
Mitsubishi has also studied treatments before epitaxial crystal growth. The surfaces of SiC substrates have
been treated by several methods, such as polishing, RIE, thermal oxidation, HF etching, and, thermal etching,
and have been observed by AFM. The use of RIE after polishing is most suitable for forming a flat surface.
Thermal etching forms a surface with crystal steps at regular intervals. The best condition for thermal
etching is an atmosphere of hydrogen, a substrate temperature of 1400C, and 30 minutes etching time.
R&D on Combustion Control System
Ion Engineering Research Institute Corporation
Ion Engineering has measured the temperature and wavelength dependencies of SiC photosensors. The
wavelength dependency measurement indicates that the SiC photosensor has a sensitivity between 200 and
400 nm and has a maximum sensitivity at 250 nm with a quantum efficiency of 0.8. This result shows that
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the sensitivity of the SiC photosensor is better than that of a Si photosensor for UV detection and that it holds
its function above 200C. However, the results indicate that the temperature and wavelength dependencies
change from device to device. In order to stabilize its sensitivity, the manufacturing method of SiC devices
needs to be refined.
A prototype of flame detector has been fabricated with the SiC photosensor evaluated above. The ignition of
a butane gas flame triggers the functioning of the detection circuit. The detector picks up UV luminescence
and sets off an alarm.
R&D ON FUNDAMENTAL STUDY FOR SiC SEMICONDUCTORS
Fundamental Study of Silicon Carbide by New Crystal Growth Method
Faculty of Engineering and Design, Kyoto Institute of Technology
The purpose of this research is to make high quality SiC epitaxial layers for devices having high breakdown
voltages. For device applications, a thick epitaxial layer is required. In the conventional CVD method,
growth rate of SiC is only about 3 m/h. This study has used a CST method (Close Space Technique) that
enables researchers to obtain thick epitaxial layers safely, simply, and more quickly.
In the CST method, an epitaxial layer is grown by sublimation. The method is basically the same as the
conventional sublimation method for boule growth of SiC. One big difference in configuration is the
distance between source and substrate. The SiC source and the substrate are closely spaced by thin graphite
spacers. Using such a configuration, unwanted free carbon from the graphite wall is minimized, and growth
is promoted under a quasi-equilibrium condition. Source materials include a 3C-SiC polycrystalline plate
with high purity and Acheson and commercially available wafers with 3.5 and 8 off (0001) toward <1120>.
On the on-axis substrate, the surface morphology depends on the polarity of the substrate. Surface
morphology of epitaxial layers grown on Si-face are smoother than the C-face. Though growth rate on the Cface is higher than on the Si-face, the morphology is rougher.
On the off-axis substrate, the surface becomes rather smooth compared with the on-axis substrate. Under a
growth pressure of 760 Torr and a growth temperature between 2200-2400C, growth rate is between 40 and
~200 m/h. The epilayer on off-axis substrate has a mirror-like morphology. However, under microscope, a
stripe-like morphology perpendicular to the <1120> off-direction appears. Researchers have also
investigated surface morphology dependence on growth parameters such as temperature and distance
between source and substrate. Photoluminescence measurement has confirmed that the epitaxial layers are of
high quality.
SiC Thin Film Formation by Ion Beam Techniques
Osaka National Research Institute, AIST
Researchers have developed new methods for SiC thin film formation using ion beams: negative and positive
ion beams deposition, negative ion beam self-sputtering, and vacuum arc plasma for its components. The
results are summarized as following: Increasing the ion beam current allows for direct ion beam deposition
of SiC in the negative and positive ion beams deposition technique. In the negative ion beam self-sputtering
technique, RBS reveals no impurities in the deposited Si and SiC films. The initial stages of growth have
also been observed, and multilayers have been formed using vacuum arc plasma.
Doping Technology by Nuclear Reaction Methods
Department of Nuclear Engineering, Kyoto University
Researchers have studied the neutron irradiation effects on 4H- and 6H-SiC crystals using electron spin
resonance (ESR), optical absorption, resistivity, and Hall effect measurements. Neutron irradiations have
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been carried out using a research reactor (KUR), a fast source reactor (YAYOI), a fast neutron source (FNS),
and an electron linac (Linac). Optical absorption and ESR spectra of 4H-SiC crystals irradiated by fast
neutrons have been measured at liquid nitrogen temperature. A broad absorption band can be observed at
about 780 nm in 4H-SiC. An ESR spectrum labeled Tl center is observed in fast neutron irradiated 4H-SiC.
The origin of the 780-nm band and Tl center have been tentatively attributed to an electron-trapped silicon
vacancy. The irradiation temperature effect for the production rate of the 780-nm absorption band has been
investigated. Results show that the production rate at 15ºK is lower than the one at 360ºK. Isochronal
annealing of neutron irradiated 4H-SiC shows that resistivity is annealed at two stages (373ºK, 523ºK) and
that about 40% resistivity is recovered.
Characterization of SiC Single Crystals by Raman Spectroscopy
Osaka University
Study of basic properties of SiC at high temperatures is important for the development of SiC devices, and a
number of electrical parameters for p-type materials should also be investigated. Establishing an optical
method for characterizing thin top layers for the study of epitaxial and ion-implanted layers is an urgent
problem. For these targets, researchers have performed mainly microscopic Raman studies and obtained the
following results: Firstly, spectral profiles of optical phonon bands have been observed in detail up to
1200C. Researchers have found that phonon-phonon interactions determine the profiles and that the effects
of thermal carriers can be neglected. The results have been applied to assessment of temperature in SiC
diodes in operation. By analyzing LO-phonon-plasmon coupled modes in heavily-doped n-type samples,
Osaka University researchers have deduced temperature variation in carrier concentration and mobility.
Secondly, researchers have observed a very weak carrier-concentration dependence for the coupled mode in
p-type samples. The intensity of the inter-valence-band transition in the low frequency region and the Fano
interference feature can be used as measures of hole concentration. Finally, a Raman microprobe system for
ultraviolet laser excitation has been developed. Researchers have tested its performance using ion-implanted
SiC samples and confirmed its superiority to systems with visible laser excitation for surface
characterization.
Optical Characterization of SiC Crystals
Institute of Space and Astronautical Science (ISAS)
High temperature electronics is regarded as a key technology for space exploration. SiC is one of the most
promising materials for high temperature electronic devices. The purpose of this study is to improve the
crystalline quality of SiC wafers through the accurate analysis of impurities and defects in SiC by
photoluminescence (PL) method. Deep-level PL has been investigated in 4H-SiC wafers utilizing below
bandgap excitation. The excitation with a photon energy of 2.54 eV induces well-defined vanadium-related
lines. Microscopic mappings of these emissions reveal that the intensities increase around macrodefects such
as cracks and hexagonal defects, although their intensity patterns are substantially different. ISAS engineers
suggest that the gettering effect of the macrodefects is responsible for microscopic intensity variations. The
strain field draws impurities and point defects participating in the deep-level PL processes towards the
macrodefects. Better understanding of the gettering effect is crucial for advanced device fabrications as is
true for state-of-the-art silicon devices.
Study on Modification of SiC Electrical Properties Using a Pulsed Laser Irradiation Method
Nagoya Institute of Technology
A p-n junction has been formed in n-type SiC by Al doping at the surface region by controlling the dopant
activation using the pulsed laser irradiation method. Similarly, a W ohmic electrode with a flat surface on ntype SiC for operation at high temperature has been formed. Furthermore, Nagoya Institute researchers have
attempted to apply the CAICISS method to analyze crystallinity within thin surface layers of SiC.
The results of these investigations are shown as follows:
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
CAICISS method is able to analyze the crystallinity of thin surface damaged layer induced by lapping
SiC that was not observed by RBS measurement method.

The formation of a W ohmic electrode with a flat morphology on SiC has been achieved using laser
irradiation with a beam homogenizer.

The laser irradiation method in SiC can be used to effectively modify electrical characteristics by
changing the dopant profile and concentration through the use of controlled laser energy density and
number of laser shots.
R&D on Study of Crystalline Surface Using STM and Silicide Electrode
Okayama University
4H- and 6H-SiC (0001) Si surfaces have been studied by scanning tunneling microscopy (STM), Auger
electron spectroscopy (AES), low energy electron diffraction (LEED), photoelectron spectroscopy (PES),
etc., where clean specimen surfaces have been prepared by chemical treatment followed by heat treatment in
an ultrahigh vacuum. Depending on the combination of chemical etchings and heat treatment temperatures,
1x1, 3 x 3, and 63 x 63 structures have been observed. Atomic structural models have been proposed
for reconstructed surfaces. Au- and Cu-deposition processes have been studied on these cleaned surfaces.
They have been found to form islands at the beginning of the deposition, and the island forming tendency has
been found to be higher in Cu than Au.
R&D on Doping into 6H-SiC
Department of Electronic Science and Engineering, Kyoto University
The impurity incorporation mechanism in chemical vapor deposition (CVD) of SiC has systematically been
investigated. Donor-type impurities such as N and P are more efficiently incorporated on a C-face whereas
the doping efficiency of acceptor-type impurities such as Al and B is higher on a Si-face. Effects of substrate
orientation and surface polarity on impurity incorporation have been revealed. The concentrations of N, Al,
and B atoms drastically decrease with increasing growth temperature, which may be ascribed to the enhanced
desorption of impurity atoms from a growing surface at high temperature. Al and B ion implantation into ntype SiC epilayers have been studied. A nearly perfect electrical activation ratio (>90%) could be attained by
high temperature annealing at 1550-1600C for Al and 1700C for B ion implantation. Mesa p-n junction
diodes formed by either Al or B ion implantation exhibit high blocking voltages of 950-1070V, which are 8090% of the ideal value predicted in the diode structure. These diodes are operational even at a temperature of
400C. B-implanted diodes show higher blocking voltages and lower leakage currents on average.
However, one severe drawback of B-implanted diodes is their poor forward conduction.
REFERENCES
Inoue, M., Y. Suzuki, and T. Takagi. 1997. Review of Ion Engineering Center and related projects in ion engineering
research institute. NIMB Nuclear Instruments and Methods in Physics Research B. pp. 1-6.
Toda, T., Y. Ueda, and A. Ibaraki. 1998. Characteristics of 4H-SiC MESFET with a Pt gate. International workshop on
hard electronics. February 3-4. Tsukuba, Japan.
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Site:
19
Japan Atomic Energy Research Institute (JAERI)
1233 Watanuki-cho Takasaki,
Gunma, 370-12 Japan
Tel. (81) 273 46 9420
Fax: (81) 273 46 9687
Date Visited:
25 July 1998
TTEC Attendees:
R. C. Clarke (report author), V. Dmitriev, M. S. Shur, U. Varshney, H. Morishita
Hosts:
Dr. M. Hagiwara, Director General
Dr. I. Nashiyama, Deputy Director, Dept. of Material Development
Dr. H. Itoh, Senior Scientist
Mr. Yoshikawa, Senior Scientist
Dr. T. Ohshima
Dr. Kojima
INTRODUCTION
In its pamphlet “Development of Radiation-Resistant Semiconductor Devices for Space Applications,”
JAERI states, “Artificial satellites in the Van Allen Belt are exposed to energetic radiation. These satellites
are equipped with many varieties of semiconductor devices, which are very sensitive to different types of
radiation. Thus, the mission life and reliability of satellites are limited by the radiation damage inflicted on
the devices. Using JAERI’s ion beam irradiation facility (TIARA) adapted for simulating the radiation
environment of space, we have been studying radiation effects on semiconductor devices for space
application and developing new radiation resistant semiconductors.”
Dr. Hagiwara, the Director General of the institute, indicated that JAERI has been engaged in the
development of space and radiation hard high temperature devices. JAERI is a semi-national laboratory, a
92% government funded facility that is open for the use by industrial and small business partners.
WHY SiC?
For space applications, the United States seems to be ahead in the high temperature radiation hard electronics
that will be needed. SiC is being pursued to demonstrate 100 times the alpha ray resistance that Si presently
is capable of. SiC will find applications in total dose tolerance and single upset event resistance with major
targets being the high temperature and high power device area. The institute estimates and demonstrates the
technical potential of SiC and encourages private sectors to adopt this technology. Japan Science and
Technology Corporation (JST) acts as a liaison for commercialization of inventions from the government
sector. When private companies wish to use JAERI inventions, collaboration occurs. JAERI also
collaborates with the electrotechnical laboratory under MITI. There is no collaboration with the United
States at the moment. Some work in cooperation with the University of Erlangen in Germany is in process.
Silicon-based device technologies lack the radiation hard qualities required of space electronics.
Takasaki Radiation Chemistry Research Establishment
Various R&D activities of radiation applications are conducted using large Co-60 irradiation facilities and
accelerators for electron and ion beams. Through these activities, many useful results have been produced in
such fields as environmental conservation and upgrading of polymers using electron beams and gamma rays.
Further R&D of advanced radiation technology is in progress by fully utilizing the ion beam irradiation
facility.
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Professor Dmitriev gave a presentation of the status of SiC high temperature materials and electronics in the
United States. Chris Clarke discussed microwave devices formed of SiC and Professor Michael Shur
discussed the modeling and fabrication of GaN-based electronics.
WHAT IS THE CRYSTAL ORIENTATION OF SiC, GaN, AND AlN GROWTH?
Mostly a 6H (0001) orientation on the Si face is needed for the substrates to grow nitrides.
ARE THERE ANY RADIATION RESEARCH STUDIES ON THE RADIATION RESISTANCE OF
NITRIDES?
Radiation hardness is a new area, but the bond strengths of nitrides are very high, which provides both wide
bandgap and radiation hard properties. Dr. John Zolper has performed ion implantation studies at Sandia.
Some implantation studies for making p-n junctions in nitrides at the Russian Ioffe Institute have been
reported, but p-type doping is difficult at present.
Dr. Nashiyama gave an excellent presentation of the ongoing radiation studies in semiconductor devices
being performed at the JAERI. Interest is focused on the radiation effects in solar cells, radiation effects on
MOS devices, and the observation of single event upsets using focused ion beams. Of particular attention
was the demonstration of the radiation tolerance of SiC devices such as MOS structures, SRAM/flip flop, and
radiation testing using both single event upset and total dose tolerance.
INDIVIDUAL RESEARCH
Dr. Itoh
Dr. Itoh, senior scientist, is working on the radiation effects in SiC to study the following:

electrical effects

defects structure and annealing

ion implantation including hot implantation and co-implantation
He has studied co-implantation in collaboration with University of Erlangen. Researchers have examined the
effects of carbon or silicon co-implants in the modification of impurity incorporation and lattice annealing.
Co-implantation
Dr. Itoh has added carbon implantation to boron or aluminum implants in 4H-SiC. Implant annealing was
performed at 1700ºC under an argon atmosphere.
Activation of aluminum and boron implants improve when additional carbon is used. The optimum dose of
co-implanted carbon is 1e 18 cm-3 for a 5e 18 cm-3 aluminum or boron dose.
Hot implantation (800°C) also improves aluminum activation.
K. Ohshima
Hot implantation (1200°C) of phosphorus is being investigated primarily because this impurity can be
created in SiC by neutron transmutation and because it provides exceptionally uniform doping. Activation of
hot-implanted phosphorus atoms has been shown with up to 5e 19 cm-3 doping using 1400°C anneals for 20
min.
For severe environments such as space MOSFETs are being investigated. SiC MOSFETs are formed in 6HSiC epitaxial layers on SiC substrates. Using 1200°C implants, no further annealing is needed. Gate oxides
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21
have been grown wet at 1100°C for 1hr. Using a gate length of 10 microns and 200 µm wide, transistors
show Vth of 3.41 V. Gamma-ray and ion irradiation studies will be performed on these devices.
Mr. Yoshikawa
Mr. Yoshikawa conducts 6H-SiC MOS structure studies. This work investigates the oxide trapped charges in
SiC MOSCAPs with the intent of employing SiC MOS devices in radiation hard environments. An oxide has
been formed at a depth of 100 nm on 6H-SiC, doped at 5e 17 using 1 hr, 1100°C wet oxidation. The oxide
has been slant etched using the gradual dipping technique into a buffered HF etch solution, and an array of
aluminum dots has been patterned on the wafer surface with oxide thicknesses varying from 10 nm to 100
nm. Devices exposed to gamma radiation (190 K Gy) reveal the presence of trapped charges by subsequent
CV measurements near the SiO2 -SiC interface and at a distance of 40 nm from the interface.
Dr. Kojima
To provide large area 3C SiC substrates for devices, Dr. Kojima is growing 3C SiC on Si substrates using
low pressure CVD and using propane, silane and TMA for aluminum doping of p-type films. He also uses
(100-200 Torr) van der Waals forces to reduce stress at the silicon SiC interface during growth. He has
grown films as thick as 20 microns in an attempt to reduce defects in the film.
An extensive laboratory tour to view the ion implant machines and growth equipment followed the
discussions.
REFERENCES
Abe, K., T. Ohshima, H. Itoh, Y. Aoki, M. Yoshikawa, I. Nashiyama, and M. Iwami. 1997. Hot implantation of
phosphorus ions into 6H-SiC. Proceedings of International Conference on Silicon Carbide, III Nitrides and Related
Materials. ICSIII-N’97, August 31-September 5, Stockholm Sweden.
Itoh, H., A. Kawasuo, T. Ohshima, M. Yoshikawa, I. Nashiyama, S. Tanigawa, S. Misawa, H. Okumura, and H. Yoshida.
1997. Intrinsic defects in cubic silicon carbide. Phys. Stat. Sol. (a):162, 173.
Itoh, H., T. Troffer, and G. Pensl. Co-implantation effects on the electrical properties of boron and aluminum acceptors
in 4H-SiC. 1998. Materials Science Forum. 264-268:685-688.
Itoh, H., T. Ohshima, Y. Aoki, K. Abe, M. Yoshikawa, and I. Nashiyama. 1997. Characterization of residual defects in
cubic silicon carbide subjected to hot-implantation and subsequent annealing. J. Appl Phys. 82 (11) 1 December.
Itoh, H., T. Troffer, C. Peppermuller, and G. Pensl. 1998. Effects of C or Si co-implantation on the electrical activation
of B atoms implanted into 4H-SiC. Appl. Phys. Lett. 73 (10):1427.
Ohshima, T., A. Uedono, H. Itoh, K. Abe, R. Suzuki, T. Ohdaira, Y. Aoki, M. Yoshikawa, T. Mikado, H. Okumura, S.
Yoshida, S. Tanigawa, and I. Nashiyama. 1997. Study on thermal annealing of vacancies in ion-implanted 3C-SiC
by positron annihilation. 1997. Proceedings of International Conference on Silicon Carbide, III Nitrides and
Related Materials. ICSIII-N’97, August 31-September 5, Stockholm Sweden.
Ohshima, T., A. Uedono, K. Abe, H. Itoh, Y. Aoki, M. Yoshikawa, S. Tanagawa, and I. Nashiyama. N.d.
Characterization of vacancy-type defects and phosphorus-donors introduced in 6H-SiC by ion implantation.
Submitted to Appl. Phys. A.
Yoshikawa, M., K. Saito, T. Ohshima, H. Itoh, I. Nashiyama, S. Koshida, H. Okumura, Y. Yakahashi, and K. Ohnishi.
1996. Depth profiles of trapped charges in oxide layer of 6H-SiC metal-oxide semiconductor structures. J. Appl.
Phys. 80 (1) 1 July.
Yoshikawa, M., H. Itoh, Y. Morita, I. Nashiyama, S. Misawa, H. Okumura, and S. Yoshida. 1991. Effects of gamma ray
irradiation on cubic silicon carbide metal oxide semiconductor structure. J. Appl. Phys. 70 (3) 1 August.
22
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Site:
Kyoto University
Semiconductor Science and Engineering Laboratory
Department of Electronic Science and Engineering
Yoshidahonmachi, Sakyo
Kyoto 606-8501, Japan
Tel.: (07) 57 53 5340 Fax: (07) 57 51 1576
www: http://matsunami.kuee.kyoto-u.ac.jp/
Date Visited:
9 June 1998
TTEC Attendees:
V. Dmitriev (report author), R. C. Clarke, H. Morishita, M. S. Shur, U. Varshney
Hosts:
Dr. Hiroyuki Matsunami, Professor
Dr. Tsunenobu Kimoto, Associate Professor
Dr. Jun Suda, Research Associate
INTRODUCTION
The research team headed by Prof. Matsunami has made great contributions in the development and
understanding of SiC growth techniques. The laboratory has developed blue LEDs based on SiC epitaxial pn structures. Currently, silicon carbide activity is focused on SiC bulk and epitaxial growth and high power
device development. Kyoto University researchers have developed a world-recognized epitaxial technique
for the growth of high quality CVD SiC material, namely step-controlled epitaxy. They have performed
detailed investigations on the growth mechanisms and surface morphology of SiC grown by step-controlled
epitaxy. High voltage (1750 V) Schottky barriers on Ti/4H-SiC were demonstrated using CVD-grown SiC
material. Al and B ion implantation in SiC is under investigation (1070 V mesa p-n diodes have been
fabricated). The laboratory is involved in the MITI-funded Combustion Control Systems Project. Recently,
a new project on GaN growth on sapphire and SiC substrate has begun.
STATUS OF ACTIVITIES AND COMMENTS
Professor Matsunami described aspects of the work in the laboratory. The research team includes 3
professors, 3 PhDs, 9 graduate students, and 6 undergraduate students. The laboratory is focusing on the
following research topics:

growth and characterization of SiC

development of SiC power devices

ultra-thin insulators for Si MOS devices

growth and characterization of GaN

III-V photonic devices on Si substrates
The laboratory is equipped with the following growth and processing machines (a laboratory tour was
provided):

setup for bulk SiC growth by sublimation

CVD growth machine for SiC epitaxy

device processing: evaporators, RIE equipment, oxidation equipment, photolithography, and rapid
thermal annealing

SiC MBE growth machine

GaN MBE growth machine
The laboratory is working in close cooperation with the Kyoto University Venture Business Laboratory
(KUVBL). The KUVBL was founded in 1997 with the financial support of the Japanese government in
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23
order to promote research on “An Atomic and Molecular Approach for the Development of Advanced
Electronic Materials” and to imbue younger researchers with the “venture” spirit. The KUVBL has state-ofthe-art characterization equipment including XPS, AFM, STM, X-ray diffractometers, and a Hall
measurement station.
QUESTIONS AND ANSWERS
Q.
How is high temperature electronics defined in Japan? What materials and products are included in
that definition? What role does the Japanese government play in supporting education, basic research,
applied research, and product development in high temperature electronics?
A.
Definition: electronics involving devices that can operate at high temperatures
materials: SiC, GaN, partly Si and their devices.
education: no special support
basic research: almost no support
applied research: For 6 years in the Kansai area, MITI has supported a local project on SiC to realize
a monitoring system for the control of combustion
Q.
Is your organization involved in any government high temperature and/or high power electronics
program?
A.
MITI provides sub-support for high temperature electronics through the Ion Engineering Research
Laboratory. The Ministry of Education has promoted research in conductivity control both in-situ and in ionimplantation high power electronics through its program “Control of Widegap Semiconductors and
Application to Energy Electronics.”
Q.
Does the company view materials and/or devices for high temperature and/or high power electronics
based on SiC and group III nitrides as products to sell? What “roadmap” do you see for high temperature,
high power electronics (similar to the famous “roadmap” for Si MOSFET technology)?
A.
High power SiC electronic devices can be sold on a commercial basis. Roadmap would be as
follows: the first 5 years would be spent on basic research.
Q.
What high temperature and/or high power component/system is your organization targeting for
development and introduction over the following time scale:
A.
1-5 years
- SiC Schottky devices
5-10 years
- SiC switching devices (MOSFET, IGBT etc.)
>10 years
Q.
In meeting these applications areas, what gaps exist in the current technology base in SiC and group
III nitrides? What are the major issues to be overcome in the following general areas?
A.
material growth, wafer quality
device fabrication, MOS interface, acceptor implantation
packaging
reliability, oxide reliability
systems integration and performance testing.
Q.
What temperature range would you consider for high temperature electronic operations?
24
DRAFT – HTE Site Reports - DRAFT
A.
250-350oC
Q.
What power level would you consider for high-temperature devices?
A.
100-1000 W
1-10 kW
Q.
In your organization, what percentage of the overall investment in wide bandgap semiconductor
electronics is directed at the development of:
A.
material growth
45%
device manufacturing processes
40%
device design and modeling
5%
packaging
0%
device testing
10%
Q.
What wide bandgap semiconductor material has the best potential for high temperature and/or high
power electronics? What semiconductor material for high temperature electronics do you expect to dominate
the market?
A.
SiC
Q.
What are the most important material characteristics for substrate material for wide bandgap
electronics?
A.
defect density
cost
size
Q.
What are the most important material characteristics for epitaxial material for high temperature and
high power electronics?
A.
defect density
electrical properties
growth rate
Q.
What are the main issues in manufacturing materials for high temperature electronics?
A.
high quality substrate
Q.
Does the university grow substrate and/or epitaxial material for high temperature electronics? What
methods are used? What technology has the best prospect for production of bulk and epitaxial materials for
high temperature electronics? Does the university buy substrate and/or epitaxial material for high
temperature electronics?
A.
grow substrate for some purpose: seeded sublimation
grow epitaxial material: CVD
buy substrates, but not epitaxial material
DRAFT – HTE Site Reports - DRAFT
25
Q.
What device building blocks (ohmic contacts, Schottky barriers, p-n junctions, device isolations,
etc.) do you consider to be bottlenecks for high temperature devices fabricated in SiC and group III nitride
materials?
A.
oxide reliability for SiC
Q.
What is the relative importance of unipolar devices (MOSFETs, MESFETs, SITs, etc.) compared to
bipolar devices (BJTs, HBTs, etc.) for devices fabricated in SiC and group III nitrides? What is the role of
super switching in high temperature, high power devices? What are specific issues in developing high
temperature sensors?
A.
depends on the kind of application
super switching?
Q.
Are the key material parameters for SiC and group III nitrides known well enough for the design of
high temperature, high power electronics?
A.
no
Q.
What are U.S. strengths in R&D for high temperature electronics?
A.
support from various financial sources
SUMMARY
This research group is leading in SiC technology. The continuing need in basic materials research, including
research and development on micropipe-free substrates, doping, and surface preparation techniques, was
emphasized several times during the discussion. New methods for bulk SiC growth should be considered.
Commercialization of SiC devices, probably power Schottky diodes together with Si IGBT power switches
and high frequency/high power devices for microwave application, is expected in 5 years. Those power
devices will be used in the early stages; then later power electric systems will need SiC devices. Prof.
Matsunami sees the largest market for SiC high temperature devices in the automotive industry in the future
when mature technologies for SiC devices have been established, but he is concerned about the cost of SiC
materials and devices.
REFERENCES
A 3C-SiC/Si 6-inch-diameter epitaxial wafer fabricated by HOYA Company was demonstrated.
Itoh, A., and H. Matsunami. 1997. Single crystal growth of SiC and electronic devices. Critical Reviews in Solid State
and Materials Sciences. 22:111-197.
Lab tour and KUVBL tour.
Matsunami, H., and T. Kimoto. 1997. Step-controlled epitaxial growth of SiC: high quality homoepitaxy. Materials
Science and Engineering. R20:125-166.
26
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Site:
Matsushita Electronics Corporation (Panasonic)
Corporate Research & Development
Electronics Research Laboratory
3-1-1 Yagumo-Nakamachi, Moriguchi
Osaka 570-8501, Japan
Tel.: (81) 726 82 7536 Fax: (81) 726 82 7783
Date Visited:
8 June 1998
TTEC Attendees:
V. Dmitriev (report author), R. C. Clarke, H. Morishita, M. S. Shur,
U. Varshney.
Hosts:
Masaru Kazumura, Director, Electronics Research Laboratory
Daisuke Ueda, Ph.D., General Manager
Yorito Ota, Ph.D., Manager
Kaoru Inoue, Manager
Takeshi Fukuda
Katsunori Nishii, Senior Staff Engineer
Hiroyuki Masato, Engineer
Toshinobu Matsuno, Staff Engineer
INTRODUCTION
Matsushita Electronics Corporation (MEC), a part of the Matsushita Electric Industrial Co. Ltd. (Panasonic),
was founded in 1952. Currently, MEC has 14,500 employees. Company sales are ¥482 billion (approx. $3.4
billion). The company is strictly limited to consumer electronics (“High volume at zero cost”).
The Electronic Research Laboratory performs R&D on compound semiconductors, mainly GaAs. The
laboratory has 4 divisions: GaAs IC, GaAs MMIC, GaAs Process, and New materials (SiGe, SiC, GaN).
The work on SiC and GaN is focused on the development of high frequency, high power electronics for
communication base systems.
GENERAL DISCUSSION
A roadmap for high power, high frequency devices was presented. For the year 2010, high frequency, high
power SiC and GaN devices are considered as products. For device production, 3-inch SiC substrates are
viewed as sufficient. A possible device application for SiC will be more than 100 W at L-band devices for
communications (base stations). SiC is considered a better substrate for nitrides (lasers and FETs) due to
better nitride epitaxial quality.
MEC does not have its own bulk growth capability and is not working on bulk growth of SiC. The
laboratory does not have SiC epitaxy (SiC epitaxial structures were bought from Cree). The laboratory
works on MOCVD of GaN and is planning to start MBE growth of GaN. Flip-chip technology is not
considered as being good for high frequency GaN FETs.
The SiC market is estimated to be about 10% of the high temperature electronics market. SiC has no
competitor for future high power electronics. GaN devices will work at lower power levels than SiC, but at
higher frequencies.
SiC and GaN are internal MEC projects; the laboratory does not have government funds.
In general, wide band gap semiconductor research will continue to grow in Japan. Currently, wide bandgap
semiconductor research is only several percents of the compound semiconductor R&D.
DRAFT – HTE Site Reports - DRAFT
27
After discussion, a report on ohmic contacts to 6H-SiC was presented. The main idea was to perform laser
annealing to improve ohmic contacts to n-type 6H-SiC (Nd-Na ~4.2E18 cm-3). For Pt, Au, Ti, and Ni
contacts, MEC obtained contact resistivities of 1e-4 ohm cm-2, 2e-3 ohm cm-2, 4e-5 ohm cm-2, and 8e-4 ohm
cm-2 , respectively.
REFERENCES
Hashimoto, T., et al. 1996. Inheritance of zinc-blende structure from 3C-SiC/Si(001) substrate in growth of GaN by
MOCVD. J. Crystal Growth. 169:185.
Ishida, M., et al. 1997. Growth of GaN thin films on sapphire substrate by low pressure MOCVD. Mat. Res. Soc. Symp.
Proc. 468:69.
Ishida, M., et al. 1997. Bowing parameter of unstrained InGaN grown by low pressure MOCVD. Technical Report of
the Institute of Electronics, Information, and Communication Engineers. ED97-127, CPM97-114 (1997-10):57.
28
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Site:
Meijo University
High Tech Research Center
1-501 Shiogama-guchi, Tempaku-ku,
Nagoya 468-8502, Japan
Tel.: (81) 528 32 1151 ex. 5064 Fax: (81) 528 32 1244
Date Visited:
12 June 1998
TTEC Attendees:
J. H. Maurice (report author), T. P. Chow, S. DenBaars, P. M. Stipan, C. Uyehara
Hosts:
Dr. Isamu Akasaki, Professor, Dept. of Electrical and Electronic Engineering,
(Professor Emeritus, Nagoya University)
Dr. Hiroshi Amano, Associate Professor, Dept. of Electrical and Electronic
Engineering
INTRODUCTION
Meijo University, a private university, is one of the largest universities in central Japan. It has 6 faculties and
14 departments covering all the fields of the social and natural sciences, as well as interdisciplinary fields. It
has a graduate school and a junior college division and also provides special course study. It began in 192628 as Nagoya Advanced Science and Technology School; in 1951 it was established as Meijo University. It
has 3 campuses in the Nagoya area, and its slogan is “Towards the Age of Human Renaissance.” In 1996,
the High Tech Research Center at Meijo was the first of its kind in Japan to focus on HTE.
Professor Akasaki is an important pioneer in the field of semiconducting GaN and related devices, a wellrecognized and highly accomplished figure in his field. The focus of his research activities is group-III
nitride semiconductors, their crystal growth, and their electrical and optical properties.
STATUS OF ACTIVITIES
There was a brief discussion of the research activities of Prof. Akasaki’s team. According to the materials
provided, Meijo’s focus is on the structural and optical properties of strained quantum wells in III-V nitrides
and their application to short wavelength lasers. Some recent projects and work include the following:

GaN-based super bright blue LEDs (450 nm, 20 mA, 12% quantum efficiency

nitrides grown by MOVPE

growth and characterization of GaN by hydride VPE

growth of cubic and hexagonal GaN by gas-source MBE

optical properties of strained layers in AlGaN & GaInN on GaN

quantum-confined Stark Effect due to piezoelectric fields in GaInN strained quantum wells

exciton effects in quantum wells

mechanism of stimulated emission in GaN and the effect of alloying

TEM characterization of GaN films on sapphire and GaAs substrates grown by hydride VPE

faulted structures in GaN grown on GaAs substrates
MAIN POINTS OF DISCUSSION: QUESTIONS AND ANSWERS
Q.
How is the vision of HTE defined in Japan?
A.
As rad-hard, high temperature, high frequency, high switching voltage/power for engines
(automotive, aerospace), the high saturation velocity of electrons. Also what Akasaki named in 1988
DRAFT – HTE Site Reports - DRAFT
29
“Frontier Electronics.” The future of photonic devices, for example, is in TV screens or in monitoring (e.g.,
atmospheric pollution monitoring).
Q.
Is your organization involved in any government HTE programs?
A.
Yes, under the Ministry of Education, Science, Sports and Culture of Japan, this High Tech
Research Center (HTRC, see above, established in 1996) is one of several such centers, its focus being HTE.
There is also involvement with projects under the Japan Society for the Promotion of Science (JSPS) and the
New Energy and Industrial Technology Organization (NEDO, a MITI member), which funds research for
combustion control systems for energy conservation. The 3 big Japanese projects for nitrides are the HTRC,
JSPS, and NEDO.
Q.
How long will it take to develop the materials?
A.
It’s hard to say, as there are bigger (more important) improvements occurring, but there is still no
substrate.
Q.
What are the major issues? What is the most difficult problem?
A.
Material growth.
Q.
What temperature range would you consider for HTE operation?
A.
The metallization is limited: At 600°C, the metallization becomes unstable, and at 800°C, it
sublimates.
Q.
What power level would you consider for high-temperature devices?
A.
100 W at several tens of GHz. The power level is always frequency dependent, and everyone is
always hungry for frequency and power.
Q.
What wide bandgap semiconductor material has the best potential for wide bandgap electronics?
A.
Diamond, nitrides, and SiC. The n-type doping is difficult to prepare in diamond, though the p-type
is easy. SiC has MOS capability, yet using it is difficult because it cannot make heterostructures. There is
also the SiC substrate problem. Nitrides can be grown on sapphire, much more cheaply than SiC at present.
If SiC substrate becomes cheaper and more available—if Cree cut its price, say—this might boost research.
Dr. Akasaki said that (at the time of the panel’s visit) nitride looks best. Judging from the past few specialty
conferences, GaN work constitutes 55% of all semiconductor research.
Q.
What are the most important material characteristics for substrate material for wide bandgap
electronics?
A.
Clearly defect density.
Q.
What are the most important material characteristics for epitaxial material for wide bandgap, high
temperature, high power electronics?
A.
Of doping uniformity, thickness uniformity, growth rate, interfaces, defect density, electrical
properties, surface properties, and cost—none of the above. The most important characteristic of the material
must be its uniformity, reproducibility, and consistency in producibility. Of course defect density at the
interfaces and doping uniformity fall under this.
Q.
What are the main issues in manufacturing materials for HTE?
A.
Clearly, defect control.
30
DRAFT – HTE Site Reports - DRAFT
Q.
Does Meijo University grow material for HTE? If so, by what methods?
A.
Yes, nitride, by MOCVD.
Q.
Is MOCVD superior to MBE?
A.
Yes, as it’s easier to do (the vapor pressure of nitride compared to As).
Q.
What device building blocks (e.g., ohmic contacts, Schottky barriers, p-n junctions, device
isolations, etc.) do you consider to be bottlenecks for high temperature devices fabricated in SiC and groupIII nitrides?
A.
Ohmic contacts, but also device isolation is not easy.
Q.
Is ion implantation for doping possible in GaN?
A.
Doubtful. Prof. Akasaki attempted 20 years ago both p- and n-type implantation—both with no
good results at that time.
Q.
What are the specific features of interconnects, passive components, and packaging for high
temperature operations? What are the barriers for the development of passive components for HTE?
A.
Resistors and capacitors. Interconnects suffer reliability problems and so are not that easy. The key
parameters for SiC and group-III nitrides for the design of high temperature, high power electronics are
breakdown voltage, thermal-conductivity, saturation velocity, and turn-on resistivity.
Perhaps as in the United States, there is a three-way split among industry, academia, and government
regarding GaN work. For SiC, the split is perhaps 40% government and 35% industry.
COMMENTS
Materials

nitrides:
most promising.

GaN:
95% optoelectronics, 5% electronics

SiC:
100% electronics (little hope in optoelectronics for SiC)
Issues

material growth

defect density control particularly
REFERENCES
Oyo-Butori International reprint of an interview with Prof. Akasaki
High-Tech Research Center Annual Report (volume of consolidated recent research, written in Japanese)
Lab tours (from window):
Phillips Expert System for X-ray diffraction characterization
MOCVD systems for nitrides
MBE
Analysis Room (buffer layer work, FIB, Hitachi TEM)
Clean Room
Lab Facility: approx. 500 m2
DRAFT – HTE Site Reports - DRAFT
31
Site:
Nagoya Institute of Technology
Department of Electrical and Computer Engineering
Research Center for Microstructure Devices
Gokiso-cho, Showa-ku
Nagoya 466-8555, Japan
Tel.: (81) 527 35 5544 Fax: (81) 527 35 5546
Date Visited:
12 June 1998
TTEC Attendees:
P. M. Stipan (report author), T. P. Chow, S. DenBaars, C. Uyehara
Hosts:
Dr. Masayoshi Umeno, Professor, Director, Dept. of Electrical and Computer
Engineering, Research Center for Microstructure Devices, NIT
Dr. Takashi Egawa, Associate Professor
Dr. Hiroyasu Ishikawa, Assistant
Dr. Kalaga Murali Krishna
Dr. Takashi Jimbo, Professor, Dept. of Environmental Technology & Urban Planning,
Graduate School of Engineering, NIT
Dr. Tetsuo Soga, Associate Professor, Dept. of Environmental Technology & Urban
Planning, Graduate School of Engineering, NIT
INTRODUCTION
The Nagoya Institute of Technology (NIT) had the first MOCVD reactor in Japan. At the time of the TTEC
panel’s visit, it had six and claimed that Japan had about 300. In 1984, NIT was first to have GaAs on
silicon. The Research Center for Microstructure Devices was founded in 1993 with its new building set up in
1997 (530 m2). Its main aim is to produce III-V compound semiconductors on silicon. It is doing basic
device science, continuing to research crystal growth of GaN (grown by MOCVD), and analyzing the
electrical and optical characteristics of III-V compounds. It plans to combine the advantages of silicon and
gallium nitride. Researchers are confident about producing GaN on Si since they have been successful with
many evaluations of GaAs on Si.
As a note, Prof. Umeno was Vice President of NIT last year, with Prof. Jimbo serving as the director of this
research center. Now, Prof. Umeno has come back to head this research center.
STATUS OF ACTIVITIES
Professor Umeno wants the speed of GaN combined with the benefits of silicon. His goal is to have the
material characteristics of stable oxide—high density, fast speed, a robust and lightweight large diameter
wafer—at low cost. He feels this can be accomplished by 3-D structures. There are problems though with
high density dislocations (>10e6 cm-2). Large residual tensile stress (2 x 10e9 dyn/cm2) leads to rapid
degradation of LED or laser diodes.
But as NIT pointed out, in 1984 it was successful with GaAs grown on silicon. Oki, IBM, MIT, and the
University of Illinois (to name a few) have used this technique. NIT’s GaAs on a Si solar cell was 22.1%
efficient. Researchers are working towards 40% efficiency with a monolithic tandem solar cell.
Dr. Ishikawa described an oil research company that is interested in a 200C high pressure light emitting and
detecting device. NIT is working with GaN material, but the main problems are the buffer layer and the soft
oxide. The bow of the wafer needs to be reduced by selective epitaxial growth.
Dr. Egawa discussed GaN on silicon. He is evaluating GaN on sapphire. But Si is less costly so it is more
desirable, especially since NIT’s work with GaAs is on Si. NIT has InGaN/AlGaN laser diodes. Dr. Egawa
32
DRAFT – HTE Site Reports - DRAFT
described the sources for various elements: Ga, Al, In, N, Si, Mg, and Zn. A graph showed GaN versus Mg
flow rate. Maximum hole concentration is 1.5 x 10e 18 /cm3 with hole mobility of 6 cm2/Vs.
He then described an aging test under DC current. It is used as a laser life test.
A GaN MESFET has been developed on sapphire. It has mesa etching (Reactive Ion Etching used – BCl3).
The Schottky contact was Pt/Ti/Au (10/40/100 nm). S=1.77, =1.04 and b (Schottky barrier
height)=0.89eV.
AlGaN layer = 0.2m
GaN layer = 2.0 m
Sapphire layer
When the Al concentration is increased, researchers observe cracks. But they do not see any polarization
dependency on the laser diode.
In the very near future, NIT will try SiC—or diamond. Its visiting scientist from India, Dr. Krishna,
presented the following information on amorphous carbon for electrical applications. He has started carbon
on a silicon heterojunction and achieved 2.1% efficiency. At first, he experienced a problem with thick
carbon peeling off. He moved from sputter to pulsed with good results and will present his findings at a
Vienna conference. He is now researching diamond on silicon.
Table Nagoya.1
Research Field and Some Equipment From Lab Tour
Field of Research
Main Equipment
Atomic layer epitaxy
Atomic layer epitaxial equipment
Physics of microstructure materials
Atomic force microscope
Optoelectronic integrated circuits
Fabrication system of nanostructure electron device
3-D integrated circuits
Deep level transient spectroscopy excimer laser
Micro-sensors
Reactive ion etcher
Precision machining for crystalline materials and
ceramics
Film-thickness measuring system
Planarization polishing for wafers
Chemical-mechanical polishing machine
Jeol transmission electron microscope
Hitachi scanning electron microscope
Seiko focused ion beam
NIT researchers believe that the big problem with GaN on Si is material epitaxy. They are focusing on
MOCVD processing. First, they need to grow high quality material; then they want to build devices. They
are planning a blue laser (AlGaN using LPCVD is thought to be the best).
MESFET N-type ohmic contact only is no problem. The high temperature behavior of the Schottky contact
is difficult. NIT has observed hysteresis curve MOS on GaN. It used SiN and SiO 2 by plasma and e-beam.
The plasma is the best method because the e-beam-deposited SiO2 was very porous. NIT has not observed
any e-beam damage though. Its experiences show that defects cause GaAs on Si to degrade rapidly. InGaN
works longer than GaAs on Si even when defect densities are the same.
DRAFT – HTE Site Reports - DRAFT
33
Professor Jimbo presented information on blue light. Originally, researchers thought that only the II-VI
compounds could emit blue light, but this is not the case.
REFERENCES
Nagoya Institute of Technology. 1997. Overview of Institute. Brochure.
NIT. Research Center for Micro-Structure Devices. (in Japanese) On processes and equipment. Pamphlet.
Technical Report at Research Center for Micro-Structure Devices. 1998. Volume 5, March. Booklet of activities from
last year.
34
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Site:
NEC Corporation
34 Miyuakigaoka
Tsukuba,
Ibaraki 305, Japan
Tel.: (81) 298 50 1149
Fax: (81) 298 50 1106
Date Visited:
10 June 1998
TTEC Attendees:
S. DenBaars (report author), T.P. Chow, P.M. Stipan, C. Uyehara
Hosts:
Dr. Akira Usui, Senior Manager, Optoelectronic Device Lab
Dr. Yasuo Ohno, Senior Principal Researcher, Ultra High-Speed Device Lab
BACKGROUND
NEC’s main business activities center on computers and communication products. The development of
human communication and culture is the company’s vision for the 21st century. In fiscal year 1997, NEC
had sales of $39 billion. The main product areas are as follows:

communications systems and equipment

computers and industrial electronics

electronic devices
Of particular interest for this report is the fact that NEC is one of the leading producers in the world of
compound semiconductor devices for communications (FETs) and photonics (laser diodes). The research for
these devices is done both at the research labs in Tsukuba and at NEC factories such as NEC Kansai
Electronics.
TECHNOLOGY DISCUSSION
Wide Bandgap Electronics
NEC is quite interested in both electronic and optoelectronic applications of wide bandgap semiconductors.
Currently NEC is focusing on GaN as researchers believe it will be the least expensive wide bandgap
material to commercialize. The GaN electronic effort was started in 1997, but Dr. Ohno had a clear picture
of the areas where he believed GaN will compete. Dr. Ohno has worked on silicon- and GaAs-based FET
devices for the last 15 years. He believes the main advantage of wide bandgap semiconductors are the large
breakdown voltage, the small Schottky gate leakage (low off-state leakage), and the small hole generation
rate (low on-state voltage). The high breakdown field and high frequency performance of GaN make it
attractive as a microwave power communication device. The higher allowable operation temperature of GaN
was also mentioned as a benefit since it allows for higher heat removal due to the increase in the temperature
gradient. In particular NEC company targets for the microwave power GaN high electron mobility transistor
(HEMT) are as follows:

100 W CW RF power GaN is targeted for 50-100 GHz region

100 W part and 500 W module

drain current density of 0.5 A/mm

low gate leakage

p-type GaN (important for on-state resistance)
Dr. Ohno believes that the GaN electronics market is primarily for high frequency satellite and
communication base station applications. For cellular phone applications, the competition will be fierce with
Si LDMOS coming to a 5 GHz power region soon. Other potential applications of wide bandgap electronics
DRAFT – HTE Site Reports - DRAFT
35
are microwave ovens and anti-collision radar for automobiles and boats. The non-toxic nature of GaN makes
it an attractive alternative to GaAs devices, and it would meet ISO 14000 specifications.
Wide Bandgap Optoelectronics
The optoelectronics effort, in particular the blue GaN laser effort, has been ongoing for several years at NEC.
Dr. Usui has achieved remarkable success in pioneering the defect reduction in GaN using a lateral epitaxial
overgrowth (LEO) method. Dr. Usui uses the acronym FIELO for facet initiated epitaxial lateral overgrowth
to describe the NEC technique for defect reduction in GaN. In this technique, having the growing facet steer
the edge defect parallel to the surface reduces defects so that they cannot propagate on the surface. The
defect density is reduced from 1E+9/cm2 to less than 1E+7/cm2. He has even made “bulk like” GaN
substrates by lifting off thick GaN epitaxial films from the sapphire substrate using a proprietary technique.
These bulk like GaN films are 100 to 200 microns thick and 1cm by 1cm wide. Such low defect films can be
used to make conventional type edge emitting lasers. Dr. Usui has developed a hydride vapor phase epitaxy
(HVPE) method for depositing the thick LEO films on sapphire substrates. The films are grown at 1000°C
and are 100 to 200 microns thick after a few hours. The best X-ray line width is 150 arcseconds, and
mobilities of 863 cm2/V sec and 2780 cm2/V sec have been obtained at 300K and 77K, respectively. The
two areas Dr. Usui mentioned that NEC is interested in are the blue laser for DVD applications and the white
LED for lighting and LCD backlighting. For the white lighting applications of GaN, Dr. Usui mentioned the
large Japanese government supported program to develop more energy efficient light sources. The blue
DVD laser will have wide ranging applications in the future high information society in which DVD drives
will be found in DVD-ROM for road maps, DVD drive for home computers, and DVD for home
entertainment. Other potential consumer applications that require higher output powers at lower costs are
blue and green laser diodes for projection displays and laser printing. NEC’s research in these areas is first
rate, and these products will no doubt be achieved.
36
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Site:
Nichia Chemicals Industries Ltd.
491 Oka, Kaminaka
Anan, Tokushima 774, Japan
Tel.: (81) 884 23 7787 Fax: (81) 884 23 1802
Date Visited:
8 June 1998
TTEC Attendees:
S. DenBaars (report author), T. P. Chow, P. M. Stipan, J. H. Maurice, C. Uyehara
Hosts:
Dr. Shuji Nakamura
Mr. S. Mukai
BACKGROUND
Nichia Chemical Industries Ltd. is the world’s leading manufacturer of GaN-based blue, green, and white
LEDs and phosphors for lighting and CRTs. The company is very entrepreneurial and was founded in 1956
by Nobuo Ogawa to develop fluorescent lamp phosphors. The company has gained worldwide recognition
for Dr. Shuji Nakamura’s achievements of bright blue, green, and white LEDs and, more recently, long life
CW blue laser diodes. Dr. Nakamura started the GaN effort in 1989 at a time when all the other
optoelectronic companies were pursuing II-VI technology. This foresight has allowed the company to
develop a large technology lead in nitride semiconductor technology.
Due in large part to its technical accomplishments in GaN materials and devices, Nichia has grown very
rapidly recently: In 1997 it had sales of approximately $330 million, compared to 1995 sales of
approximately $200 million (Nichia 1997). The company is privately held and proud to be a major employer
for the people of Shikoku Island.
TECHNOLOGY DISCUSSION
GaN Light Emitting Diodes
Nichia controls the market for wide bandgap GaN LED devices and is selling approximately 20 million
LEDs every month. At the time of the TTEC panel’s visit, the best external efficiency Dr. Nakamura has
achieved for the blue and green LEDs is 10% and 12% external quantum efficiencies, respectively. The
white LEDs are approximately 5% efficient and have a luminous efficacy of 10 lumens/watt, which is
becoming competitive with existing incandescent sources. Nichia is only interested in the optoelectronic
applications of GaN and is not pursuing high temperature electronic applications.
When asked about the high temperature performance of GaN LEDs, Dr. Nakamura mentioned that the newly
developed amber LEDs are far superior to conventional AlGaInP amber LEDs. The wavelength shift as a
function of temperature is much smaller in GaN than in GaAs-based LEDs. He showed a comparison of
InGaN to AlGaInP-based LEDs at an elevated temperature of 80°C in which the InGaN LED light output is
decreased by only 20%, whereas the AlGaInP LED light output is down by 70%. This excellent temperature
performance for GaN-based LEDs in comparison to conventional GaAs-based LEDs is also seen when GaNbased LEDs are compared to GaP green and AlGaAs red LEDs (Nakamura and Fasol 1997). The InGaN
yellow LEDs are not as bright as transparent substrate AlGaInP LEDs, but their performance rivals absorbing
substrate AlGaInP LEDs. At 20 mA, the new yellow LED is 4 candela and has an external efficiency of
3.3% at 594 nm (Mukai et al. 1998). Dr. Nakamura has successfully operated the GaN LEDs at maximum
temperatures of 120°C for a packaged lamp and 300°C for a bare chip. Recently, Nichia developed a 2%
efficient UV (372 nm) LED. UV LEDs are expected to find new applications in UV plastic curing, lighting,
sterilization, medical, and counterfeit currency detection. Nichia’s LED products have many new markets.
Dr. Nakamura emphasized that GaN is the most “environmentally friendly” LED material available. In
comparison to toxic GaAs LEDs or even mercury-containing fluorescent lamps, GaN offers a truly safe
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37
lighting solution. Dr. Nakamura is very optimistic that the GaN LED will improve the energy efficiency of
lighting and be beneficial to the environment.
GaN Blue Laser Diodes
Nichia was the first company in the world to successfully achieve a blue laser diode in a GaN materials
system. Initially the GaN lasers lasted only a few seconds, but reliability has improved dramatically to a
point where Dr. Nakamura has achieved CW operation for up to 4000 hours at room temperature. Elevated
temperature testing at 50°C has projected that the actual lifetime is in excess of 20,000 hours at 2 mW. The
highest CW output power previously achieved was 400 mw. A key development in obtaining reliable CW
laser performance has been defect reduction by using an epitaxial lateral overgrowth GaN (ELOG) substrate.
In this technique a silicon dioxide mask is propagated by block dislocation, and a “defect free” film is
achieved in the laterally overgrown region. After 100 microns of growth, a fully coalesced GaN thin film is
achieved, and a proprietary process removes the sapphire substrate. The ELO process will be described in
more detail in the section on GaN materials. Laser diodes with InGaN/GaN multiple quantum well (MQW)
active regions are then grown on top of this virtual bulk GaN substrate. The active regions are then defect
free and can survive under high current operation (3 kA/cm2). The panel was shown a CW blue laser diode
housed in a small held package being run off a watch battery. Dr. Nakamura believes that a blue laser diode
product will be available soon from Nichia. Nichia is developing the laser for use in the largest market first,
that being the next generation of high density digital versatile disc (DVD) optical storage systems. Current
estimates are that the reduction in spot size that can be achieved with blue GaN lasers will yield a storage
capacity of 15 GB per conventional size compact discs, enough for recording a full-length motion picture in
high resolution mode.
When asked what the most important technology for high quality GaN is, Dr. Nakamura mentioned crystal
growth. In particular, Nichia’s proprietary 2-flow metalorganic chemical vapor deposition (MOCVD) is one
of the key technologies for achieving high quality GaN materials and devices. The defect reduction
technique of ELOG defect free substrate also plays a major role in achieving long life reliable laser diodes.
GaN LED Traffic Signals
One of the most impressive demonstrations of GaN technology the panel saw during its Japan trip was the
LED traffic signal demonstration. Nichia had constructed a large outdoor display comparing LED-based
signals to incandescent-based signal heads. The brightness, color, and viewing angle of the LED traffic
signals was as good or better than the conventional 70 watt (Japan) incandescent light-bulb plus filter. The
savings in energy is tremendous (See Table Nichia.1), and the payback period based on energy savings alone
is 1 to 3 years. Given that the solid-state reliability and lifetime of the LED signal head is at least 5 years,
maintenance costs and safety are much improved for LED traffic signals. The impact of this energy savings
alone is enormous, and if all the traffic signals in Japan were switched to LEDs, the move would save the
construction of at least one nuclear power plant. This clearly is an area where GaN technology will have an
impact on the public.
Table Nichia.1
Traffic Signals Comparison to 70 W Japanese Standard
Color
Power in
LEDs
Savings
On-Time
Red
Yellow
Green
17 W
36 W
7W
53 W
24 W
63 W
55%
5%
45%
COMPANY TOUR
The panel was allowed to visit the impressive product showroom of Nichia and to witness some recently
developed products. Along with Nichia’s wide range of GaN LED colors, a full-color large screen LED TV
was on display. Nichia LEDs have been used to build even larger screen (building size) LED TVs. These
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can be seen at major Shinkansen (bullet train) stations like Nagoya (See Fig. Nichia.1). The LED TV is
particularly impressive because of the wide range of colors afforded by the color purity in the green (520 nm)
and blue (470 nm) LEDs, in comparison to less color-pure phosphors. Nichia has also developed a white
foot-lamp and overhead multi-color reflector lamp. Other emerging products using GaN LEDs are a compact
color scanner, a LCD backlight, an automobile dashboard backlight, and UV LEDs for counterfeit currency
detection. During the product discussion, Dr. Nakamura also displayed Nichia’s most recent product
successes, including a CW blue laser pointer, amber LEDs, and newly developed UV LEDs.
Fig.Nichia.1. LED TV
REFERENCES
Mukai, S., H. Narimatsu, S. Nakamura. 1998. Amber InGaN-based LEDs operable at high ambient temperatures. Jap.
J. Appl. Physics. p. L479.
Nakamura, S., and G. Fasol. 1997. The Blue Laser Diode. Heidelberg, Germany: Springer Verlag, p. 184.
Nichia. 1997. Company Profile. Company Information Brochure.
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Site:
Satellite Venture Business Laboratory
Dept. of Electrical Engineering
Tokushima University
2-1 Minami-Jyosanjima-cho
Tokushima 770, Japan
Tel.: (81) 886 56 7446 Fax: (81) 886 56 9060
Date Visited:
8 June 1998
TTEC Attendees:
S. DenBaars (report author), T.P. Chow, P.M. Stipan, J.H. Maurice, C. Uyehara
Hosts:
Prof. Shiro Sakai
Dr. Katsushi Nishino
Dr. Yoshiki Naoi
39
BACKGROUND
The Satellite Venture Business Laboratory (SVBL) at Tokushima University is 1 of 24 national labs created
from the Ministry of Education’s supplementary budget to stimulate the creation of new ideas and new
businesses. The SVBL at Tokushima University is a 4-story world-class facility that opened in June 1997
with research focused on the “Nitride Photonic Semiconductor.” Key strengths of SVBL are the excellent
materials characterization facilities, bulk GaN crystal growth, and thin film deposition. Currently, there are
several Ph.D. candidates, master’s, and bachelor’s students, and 4 foreign post-doctoral researchers working
on wide bandgap semiconductors. The SVBL facility is establishing an international reputation and
welcomes visits from outside faculty and researchers.
TECHNOLOGY DISCUSSION
The discussion centered on recent results obtained in Professor Sakai’s group and on applications of nitrides
in electronics. The group is pioneering in bulk GaN crystal growth by sublimation. It has achieved bulk
GaN crystal a few mm in diameter. It has also deposited epitaxial layers on these crystals by MOCVD.
These bulk crystals have lower defect densities than GaN grown on sapphire. One particularly interesting
discovery from the SVBL group is the role of defects on the cathodoluminscence (CL) properties of GaN.
Professor Sakai and his students recently observed that defects do indeed lead to dark spot regions. In a
comparison of GaN grown on sapphire and bulk GaN, they observed almost no dark spots on the bulk like
film. The number of dark spots on the GaN on sapphire appears to correlate with the defect density measured
by TEM. Therefore by growing on bulk GaN crystals, one can expect the optical properties to be improved
in the future. This work was reported at the 2nd International Conference on Nitride Semiconductors (ICNS2) and was well received by the community (Suguhara et al. 1998). In addition to the bulk GaN work,
Professor Sakai is developing 2-inch GaN wafers in his MOCVD system, which can then be supplied to
outside researchers. In the course of his crystal growth research, he has found that when grown on sapphire,
GaN low temperature buffers are better than AlN buffers. When asked about MBE technology for GaN
growth, Professor Sakai strongly believes that MOCVD has higher quality and will lend itself to massproduction better.
While the focus of the University of Tokushima is on photonic applications of the nitrides, Professor Sakai is
quite knowledgeable and interested in the electronic applications as well. An interesting position that
Professor Sakai and other Japanese researchers disclosed to the panel is that the “environmentally friendly”
nature of GaN and SiC, as opposed to GaAs, is a big incentive for commercial acceptance in the Japanese
market. He cited the example of the many cellular phones being used in Japan that contain toxic GaAs chips,
which may one day be replaced with GaN or SiC chips. Another application is in the area of “hard
electronics.” This term applies to semiconductors that can tolerate harsh environments and be run at high
powers and high temperatures. He emphasized if the cost of the new wide bandgap devices can be made
competitive, then consumers may favor the safer compounds.
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LAB TOUR
The panel was given an extensive lab tour of all the SVBL facilities at Tokushima University. Inside a large
clean-room, complete processing facilities for blue lasers and LEDs are housed. Two large crystal growth
systems, one a MOCVD system and the other a bulk GaN sublimation system, were in full operation. The
panel viewed a 2-inch diameter wafer grown in the MOCVD system. It appeared to have a clear mirror-like
surface with no signs of large defects. The characterization facilities were excellent, containing high
resolution TEM, cathodoluminescence, SEM, secondary ion mass spectroscopy (SIMS), multicrystal X-ray
spectrometry, Auger spectrometry, and a low temperature photoluminescence setup.
REFERENCES
Suguhara, T., H. Sato, M. Hao, Y. Naoi, Y. Kurai, S. Tottori, S. Yamashita, K. Nishino, S. Sakai. 1998. Jap. J. Appl.
Phys. 37 (4a):L398.
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Site:
Sony Corporate Research Center
174, Fujitsuka-cho, Hodogaya-ku
Yokohama-shi 240-0031, Japan
Tel.: (81) 453 53 6866 Fax: (81) 453 53 6905
Date Visited:
11 June 1998
TTEC Attendees:
J. H. Maurice (report author), T. P. Chow, S. DenBaars, P. M. Stipan, C. Uyehara
Hosts:
Dr. Hiroji Kawai, Chief Research Scientist, N Project
Dr. Masco Ikeda, Project Leader, N Project
Mr. Hiroshi Ooki, General Manager, Materials Research Laboratory
41
INTRODUCTION
Our hosts first provided a briefing on the Sony Research Center’s business structure. The center has
electronic components and devices groups. Structurally, there are two companies: a semiconductor company
and a components and computer peripherals company. Mr. Ooki briefed the panel on the center’s structure
and general activities (details under that heading, below). Within the bigger picture, the focus then moved to
work within three entities:

Materials Research Lab

GaN work (N Project)

Kuboto Lab
Regarding high-temperature electronics and wide bandgap work, the center is primarily a GaN facility.
Discussion of its GaN work included a comparison with GaAs and a tour of the GaN (or “N”) project area.
STATUS OF ACTIVITIES AND COMMENTS
Growth is the most important issue to the N Project people, indeed the main focus of work at the facilities
toured. Process is next in importance. For that, the researchers particularly follow the lead of Dr. DenBaars’
work. In fact, an engineer at Sony (Dr. Uchida) is currently working in Dr. DenBaars’ University of
California at Santa Barbara group.
The core of Sony’s technical presentation was based on a GaAs and GaN comparison of key material
parameters for the two semiconductor materials:

drift velocity

velocity overshoot

transport time

band line-up & Ec (for various Al concentrations in respect systems)

physical properties
The advantages a GaN-based FET offer are as follows:

high peak velocity

high saturation velocity

high electric-field transport

high EC

high 2D electron gas concentration (“2DEG”)

high breakdown voltage
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GaN offers these characteristics in a stable material with large-area substrate (sapphire) available. For
transport devices, 2DEG in GaN is highly desirable since with reduced dimensionality, electron mobility
becomes high. This cannot be done in SiC.
Cornell University researchers in this area (under Prof. Lester Eastman) have calculated a transit-time
comparison of the two materials (GaAs vs. GaN). Dr. Kawai mentioned that Sony’s results of 230 mS/mm
of transconductance for GaN FETs is too low and that it is smaller than calculated. The drift velocity must
be much higher, and he attributes the problem to surface roughness and dislocations, as well as poor contacts.
That is, growth issues remain a central concern.
Some of the problem areas (bad features) are:

less high quality epilayers

low thermal conductivity of sapphire substrate

conventional processing techniques (problematic here)
All in all, the implications of the comparison for FETs is that the piezoelectric effects in the AlGaN/GaN
system’s heterostructure allow for a built-in 2DEG effect, thus making a high-temperature, high-power GaN
FET device both attractive and possible. Since GaN could then replace GaAs, certainly it can compare with
GaAs in devices.
Among the challenges to meet for device fabrication are the following:

low field mobility (dislocation limited by 10 9 cm-2 dislocations)

ohmic contacts & ohmic deep alloying

etching

implantation doping
Is high electron mobility transfer (HEMT) the best structure for a transport device? Well, given the wide
bandgap, the built-in 2DEG concentration, and the high Schottky barrier height, if no deep levels are in the
AlGaN layer, then a hetero MIS-HFET is possible, and Sony proposes such. (The MISFET is not created by
an inversion structure, though an inversion mode is very possible.)
Evident from plots of the conduction-band lineup in the Sony metal/AlN/n+GaN/AlGaN structure, the
channel carrier decreases as the AlN thickness decreases. Using a very thin A1N layer, Sony researchers
thus have succeeded in fabricating the first GaN IG-HFET. They expect AlN/GaN HFETs to be the most
promising structures for HTE and high frequency devices.
Regarding blue laser work, Sony’s continuous (CW) blue laser had not been made public at the time of the
TTEC panel’s visit; that is, no details had yet been published, and information was shared by verbal mention
only. Sony projects that an optical storage device using blue lasers will be available in 2000 or 2001.
Many device structure improvements have been made in Sony’s blue laser diodes. Among these are the
following:

operating voltage
Vop <5 V

threshold current density
Jth 500 Amps/cm2

dark spot density
DSD < 3 x 103cm-2
This is for a blue-green ZnMg /ZaSSe /ZnCdSe /ZnSSe /ZnMgSSe structure. In the future of next-generation
optical disk systems, they must have a low power consumption, a lifetime greater than 10,000 hours, and an
optical output power of approximately 30 mW. The systems must also feature a high quality laser beam.
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43
GENERAL ACTIVITIES
The Materials Research Center has 4 divisions. These are the 1) Materials Research Lab (with a staff of
about 80 researchers), 2) Magnetic Recording Research Lab, 3) Frontier Science Research Lab (which
includes advanced devices), and 4) Display Technology Lab. Activities within the Materials Research
Center include:

II-VI semiconductor compounds

GaAs optoelectronic integrated circuits (OEIC)

High-frequency devices

Li-ion batteries

Solar batteries

Organic electro-luminescence (EL, on large area, single substrate, thin films)

Dye polymer recording materials

Display materials
At the Kuboto Laboratory, there are optoelectronic (OE), nonlinear optic (NLO), and solid-state laser
(materials processing) labs. Projects at the Kuboto Lab include the aforementioned GaN work and also a
ferroelectrics lab. Kuboto also includes the Center for Environmental Technology (staff of about 50), the
Center for Materials Analysis (which is primarily involved with characterization), and the Center for
Technical Information. As for activities within the Center for Environmental Technology, they include
reclamation technology (based on polystyrene with the citrus-based oil, limonene, and flocculants from
polystyrene), ecological materials (such as lead-free solder, biodegradable plastics, and cellulose-based
molds, and life-cycle assessment (of energy-related materials such as solar cells). Researchers there have
developed a new recycling system for the foam packaging material EPS (or expanded polystyrene) and foam
molds using limonene. EPS is mostly air (with a 1/20 volume ratio). Recovered waste EPS is dissolved by
limonene at the recycling plant. The limonene and high-quality polystyrene are recovered in the process.
LAB TOUR
Sony has many MOCVD reactors, all of which are constructed and maintained there. The researchers
mentioned that horizontal 2-flow, in their opinion, is the superior growth method. A photoluminescence test
station is used in situ, basically as a monitoring tool between growth steps of GaN epilayers. The station
measures conductivity via electron mobility. An X-ray “double crystal X-ray” diffractometer measures
lattice spacing and mismatch via strain.
MAIN POINTS OF DISCUSSION
Q.
What is the future market for microwave power devices?
A.
The most promising application Sony researchers see is industry use in base-station-to-base-station
communications. This is highly desirable as digital systems are spreading and fewer stations will be needed.
The high frequency range for GaN (from 2.5 GHz to 30 GHz) means that GaN-based microwave power
devices could also replace vacuum tube technology. GaN has bigger consumer applications than GaAs. SiC
does not have as many consumer applications. SiC may become a replacement for Si devices only. In the
20-30 GHz range, many and varied laser and LED consumer applications exist.
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In lighting devices, a microwave lamp is available (from Fusion, a U.S. company, stateside). In this lamp,
microwaves stimulate sulfur, and light is emitted very efficiently. Maybe microwave devices can be used for
this. Currently microwaves are produced in a magnetron tube. A much smaller generating device would be a
very good thing. Another consumer application lies in cellular car-to-car communications, since high levels
of microwave radiation are not good for anyone. Another application is a personal uplink to space satellites,
which requires high frequency and high power.
The amount of value added to a device is important in assessing consumer applications.
Q.
Between the fabrication process and material growth, which is the main issue at present for HTE?
A.
Both are experiencing problems.
REFERENCES
Imanaga, S., and H. Kawai. 1997. Novel AlN/GaN insulated gate heterostructure field effect transistor with modulation
doping and one-dimensional simulation of charge control. Journal of Applied Physics. 82 (II):5843-5858. Reprint.
Kawai, H., M. Hara, F. Nakamura, and S. Imanaga. 1998. AlN/GaN insulated gate heterostructure FET with regrown n*
GaN ohmic contact. Electronics Letters. 34 (6, 19 March):592-393. Reprint.