bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Nanofabrication Process for InAs/AlGaSb Heterostructures Utilizing Atomic Force Microscope Oxidation
Authors: Shigehiko Sasa Shigehiko Sasa , Takatoshi Ikeda Takatoshi Ikeda , Masato Akahori Masato Akahori , Atsushi Kajiuchi Atsushi Kajiuchi , Masataka Inoue Masataka Inoue
Published: October 2002

We demonstrate a novel nanofabrication process for InAs which is shown to be readily applicable to the fabrication of InAs-based nanostructure devices that employ quantum dot or wire structures. The fabrication process is achieved by direct local oxidation using an atomic force microscope (AFM).
This is based on the oxidation of an InAs layer instead of oxidizing a GaSb surface layer which we recently demonstrated for the fabrication of InAs/AlGaSb nanostructures. Oxidation characteristics were studied and fabrication capabilities for commonly used chemical solutions were examined for the development of a simple nanofabrication process. We found that the oxidized InAs becomes insoluble to the acetic-acid-based etchant enabling a selective formation of InAs islands with a desired shape that are drawn by AFM oxidation. We comparatively describe the oxidation characteristics for both InAs and GaSb and discuss the feasibility of the new AFM oxidation process for InAs as a nanofabrication process.
Electrical Evaluation of Dry Etching Damage on the Side Wall of Mesa Structure
Authors: Yamamoto Norio , Mawatari Hiroyasu , Kishi Kenji
Published: October 2002

We propose a method for evaluating the electrical properties of damage on the sidewalls
of mesa structures. In the method, current flowing through the mesa sidewalls (I
mesa) is obtained
from the forward current-voltage (I
F-V) characteristics for Schottky barriers formed on both the
sidewalls of the mesa structures and (100) surface. In applying the method to evaluate the damage
on the sidewalls of InP mesa structures fabricated by reactive ion etching (RIE) with methane
(CH4)/hydrogen (H2), we found that Schottky barrier height φ on the mesa sidewalls is increased
by RIE. This suggests that an n-type damage layer is induced by RIE on the sidewalls. We also
found that the damage could be induced on the mesa-sidewall at least with comparable density to
that on the (100) surface, and to a depth less than that on the (100) surface.
Photoreflectance Characterization of a Channel Layer of InAlAs/InGaAs High Electron Mobility Transistor Wafers
Authors: Sugiyama Hiroki , Yokoyama Haruki , Wada Kazumi
Published: October 2002

Using room-temperature (RT) -photoreflectance (PR), we have
succeeded in characterizing InGaAs channel layers of InAlAs/InGaAs high
electron mobility transistors (HEMTs). The relationship between PR
spectra and sheet carrier density (N

s
) is discussed. The valleys observed in
the PR spectra correspond to the transitions between the quantized levels in
the valence and conduction bands. A valley shift to the lower energy side is
observed with increasing N

s
, which corresponds to the shift of the
intersubband energies. The calculation of the intersubband energies
supports the results of the PR measurements. PR spectroscopy is quite
promising for the non-destructive characterization of N

s
of InAlAs/InGaAs
HEMTs at RT.
Influence of Strain Compensation on Structural and Electrical Properties of InAlAs/InGaAs HEMT Structures Grown on InP
Authors: Letartre Xavier , Rojo-Romeo Pedro , Tardy Jacques , Bejar Moez , Gendry Michel , Py Marcel André , Beck Matthias , Bühlmann Hans Jörg , Ren Lin , Villar Constantino , Sanz-Hervas Alfredo , Serrano Jose Javier , Blanco Jose Maria , Aguilar Miguel , Marty Olivier , Soulière Véronique , Monteil Yves
Published: October 2002

Strain-compensated InAlAs/InGaAs HEMT structures, grown on InP substrate, have been
investigated in terms of structural and electrical properties. From detailed x-ray diffraction (XRD)
investigations the compensation index and the evolution of the strain state were measured. We
show that a partial and controlled strain compensation significantely improves the structural quality
and the thermal stability of HEMT structures as well as their electrical properties.
Effects of Oxidation Ambient and Low Temperature Post Oxidation Anneal on the Silicon/Oxide Interface Structure and the Electrical Properties of the Thin Gate Oxide
Authors: Cho Won-ju , Kim Yeong-cheol , Kim Eung-soo , Kim Hong-seok
Published: October 2002

Electrical properties of ultra thin gate oxide in thickness of 4 to 10 nm have been
evaluated, manufactured either by wet or dry oxidation process. The relationship
between silicon/oxide interfacial structure and the electrical properties was analyzed. In
addition, the effect of post oxidation annealing (POA) temperature on improvement of
the electrical characteristics of the gate oxide has been evaluated when the temperature
was lower than 950°C, the conventional POA temperature. The leakage current of the
ultra thin gate oxide was found to increase as the thickness decreased. The accelerated
degradation of breakdown characteristics was observed as the thickness decreased below
7 nm. The physical properties of the silicon/oxide interface were found to depend on
oxidation ambient and POA temperature. The wet oxidation process resulted in a
smoother surface than the dry oxidation process did. The POA treatment further decreased the micro-roughness of the silicon/oxide interface. The electrical properties of
the gate oxide were found to be closely related to the micro-roughness of the silicon/oxide interface. Good electrical properties were obtained for the gate oxide
manufactured by the wet oxidation process followed by the POA
treatment at 850°C.
Improvement of Internal Quantum Efficiency in 1.55 µm Laser Diodes with InGaP Electron Stopper Layer
Authors: Abraham Patrick , DenBaars JoachimPiprek , Bowers John E.
Published: October 2002

This paper investigates the effect of the conduction band offset energy at the interface between the separate confinement layer (SCL) and the p-cladding on the temperature behavior of InGaAsP lasers emitting at 1.5 µm. The performance of a laser structure incorporating an additional In0.81Ga0.19P barrier at that interface is compared to that of a regular laser structure. The results are analyzed using a comprehensive simulation software. It is shown that the current leakage at the SCL-p-cladding interface is not the dominant current loss mechanism at room temperature. However, at a higher temperature an additional InGaP electron stopper layer can efficiently reduce the electron leakage current. Finally, our measurements show that above a critical temperature the absorption loss increases dramatically.
Sidemode Suppression of Optical Add-and-Drop Multiplexer Utilizing Vertically Coupled InGaAsP Waveguides
Authors: Horita Masayoshi , Tanaka Shinsuke , Matsushima Yuichi
Published: October 2002

A sidemode suppression for a vertically and contra-directionally coupled semiconductor
waveguide-type optical add-and-drop multiplexer is investigated theoretically and experimentally,
by introducing a window function to a grating width. Grating configuration dependence of device
characteristics was numerically calculated based on the finite element method and the coupled-mode equations. It was found that the sidemode suppression ratio (SMSR) could be improved to
be more than 30 dB even by a simple linear changing of the grating width. In the device
fabrication,
a trimmed grating was formed by a multi-step exposure method, including an interferometric exposure and a laser beam direct drawing. SMSR of 18 dB was obtained for a fabricated device, and
improvement was obvious in contrast with a uniform grating. A comparison between the calculated and experimental results is also given.
Fabrication and Optical Properties of One Period of a Three-Dimensional Photonic Crystal Operating in the 5–10 µm Wavelength Region
Authors: Noritsugu Yamamoto Noritsugu Yamamoto , Susumu Noda Susumu Noda
Published: October 2002

A three-dimensional photonic crystal with one period of an asymmetric face-centered cubic structure is fabricated by utilizing a wafer fusion and a laser-beam-assisted
alignment technique. By measuring the transmission spectrum of the photonic crystal for normal incidence (<001 > direction), it is shown that ∼16 dB attenuation is successfully achieved which agrees well with the theoretical calculation.
For various incidence angles from <001 > (Γ-X') to around <110 > (Γ-K) direction, it is found that the wavelength at which the transmission becomes minimal is shifted to the longer wave-length side together with the increase of the transmission. The shift of transmission can be qualitatively explained by the change in the band structure for the propagation direction.
Silicon-Hydrogen Bonds in Laser-Crystallized Polysilicon Thin Films and Their Effects on Electron Mobility
Authors: Kitahara Kuninori , Hara Akito , Nakajima Kazuo , Okabe Masahiro
Published: October 2002

In this paper, we describe the behavior of H atoms in laser-crystallized poly-Si for
thin-film transistors on liquid crystal display panels, where H atoms were introduced by
plasma hydrogenation in order to improve mobility. Mobility was determined by the Hall
effect measurement. Si-hydrogen bonds were analyzed by Raman scattering.
By short-time hydrogenation, the introduced H atoms terminate the dangling bonds in the Si–H
configuration mainly at the grain boundaries, which results in the improvement of
mobility. With excessive hydrogenation, Si–H2 bonds are generated simultaneously with
the degradation of mobility. Si–H2 bonds are mainly formed at the in-grain defects.
Hydrogenation using the hot-wire method was also carried out and it was shown that
plasma damage does not influence the hydrogenation effects. The relationship among
Si–H2, mobility and the amount of in-grain defects was discussed, based on impurity
scattering and weak-bond models.
Photoluminescence of the MgSO4:Tb3+,Na+ Powder Phosphor
Authors: Nobuhiko Yamashita Nobuhiko Yamashita , Takuya Hamada Takuya Hamada
Published: October 2002

MgSO4:Tb3+,Na+ powder phosphors were prepared by the solid-phase reaction. The obtained phosphors were stored in evacuated glass ampoules to prevent them from being converted into hydrous magnesium sulfate by the atmospheric moisture. The photoluminescence spectra and excitation spectra were obtained at 10, 80 and 300 K. Many narrow bands were observed in both the spectra, and were attributed to the transitions within the 4f
8 electron configuration in Tb3+.
Fabrication and Microstructure of All In-plane Aligned A-Axis Oriented Superconductor/Insulator/Superconductor Junctions
Authors: Masashi Mukaida Masashi Mukaida , Masanobu Kusunoki Masanobu Kusunoki , Shigetoshi Ohshima Shigetoshi Ohshima
Published: October 2002

All in-plane aligned a-axis oriented YBa2Cu3O
x
/Gd2CuO4/YBa2Cu3O
x
superconductor/insulator/superconductor (SIS) junction structures are fabricated by a pulsed laser deposition technique and their microstructures are characterized.
An insulating barrier of Gd2CuO4 with an atomic graphoepitaxial relation is selected from a lattice-matching point of view for the b- and c-axes of YBa2Cu3O
x
at a deposition temperature of the YBa2Cu3O
x
films.
Preferred orientations and in-plane alignments of electrodes of YBa2Cu3O
x
films and barriers of Gd2CuO4 films are confirmed by X-ray diffraction spectroscopy and an X-ray φ-scan technique.
X-ray diffraction measurements revealed that all the YBa2Cu3O
x
/Gd2CuO4/YBa2Cu3O
x
films are a-axis oriented.
The c-axes of the layers are also in-plane aligned.
Measurement of Coherent Backscattering Phenomena in Emulsion
Authors: Mitani Shujiro , Sakai Keiji , Takagi Kenshiro
Published: October 2002

Coherent backscattering measurement was applied for the study of
microstructures in emulsified liquids. An enhanced component towards the
backscattering direction emerges superimposed on the diffuse light scattering from a
sample with randomly dispersed scatterers, giving evidence of the weak localization of
light in random systems. Accurate measurement of the coherent backscattering peak
gives us information on the optical transport mean free path in the sample, which leads
to an estimation of the droplet size in emulsion. A new measurement system was
developed and the clear backscattering peaks were successfully observed for various
kinds of emulsions. The key technique of the present experiment was to decrease the
laser speckle by stirring the liquid. The result obtained for heptane/AOT/water
emulsion was qualitatively related to the droplet size which could be controlled by
changing the amount of added salt. The effect of excluded volume on the scattering
mean free path was discussed.
Determination of Minority-Carrier Lifetime in Multicrystalline Silicon Solar Cells using Current Transient Behaviors
Authors: Mulati David , Fuyuki Takashi , Matsunami Hiroyuki
Published: October 2002

Mesa structures of different diameters (0.2–1.2 mm) are used to determine bulk minority-carrier lifetime based on current transients in multicrystalline silicon (Mx-Si) solar cells. Single-shot nanosecond rise time pulse testing is used for Mx-Si diodes to reveal unique information not obtained by conventional direct- current electrical testing. In this paper, effective lifetime is extracted from the recovery switching transient that is dominated by surface recombination effects. The perimeter/area ratio from different sizes of mesas removes the effect of perimeter recombination. The minority-carrier lifetime is determined as 85 µs (high efficiency, 13.37%) for sample A and 21 µs for sample B (low efficiency, 5.22%) made from the same Mx-Si ingot. The similar method gives 105 µs for Czochralski silicon (Cz-Si). The surface recombination velocities were 2800 cm/s for sample A, 5800 cm/s for sample B of Mx-Si, and 4700 cm/s for Cz-Si. This confirms that the recovery-switching transient is a suitable method for determining the minority-carrier lifetime in Mx-Si solar cells.
Short-Time DC Breakdown Phenomena in BaTiO3-Based Multilayer Ceramic Capacitors
Authors: Zhou Yuanxiang , Yoshimura Noboru
Published: October 2002

In this work, DC breakdown behavior in BaTiO3-based multilayer
ceramic capacitors is studied. It is found that the current–voltage
curves during the breakdown test change after prestressing at low
temperature, while at high temperature, the current does not show any
change. After measuring the breakdown voltage before and after
prestressing, it was confirmed that homo space charge is accumulated
near the cathode at low temperature. This causes the increase and
decrease of current with and without polarity reversal after
prestressing, respectively. However, that no space charge effect can
be observed is due to the considerable thermal effect on DC breakdown
at high temperature in multilayer ceramic capacitors.
Piezoelectric and Dielectric Properties of Fe2O3-Doped 0.57Pb(Sc1/2Nb1/2)O3–0.43PbTiO3 Ceramic Materials
Authors: Kim Jin-Soo , Kim So-Jung , Kim Ho-Gi , Lee Duck-Chool , Uchino Kenji
Published: October 2002

High-power piezoelectric materials are presently being extensively developed for applications such as
ultrasonic motors and piezoelectric transformers. In this study, the piezoelectric and dielectric properties
of Fe2O3-doped 0.57Pb(Sc1/2Nb1/2)O3–0.43PbTiO3 (hereafter 0.57PSN–0.43PT), which is the morphotropic
phase boundary composition of the PSN–PT system, were investigated. The maximum dielectric constant
(ε
33/ε
0=2551) and the minimum dielectric loss (tan
δ=0.51%) at room temperature were obtained at
Fe2O3 additions of 0.1 wt% and 0.3 wt%, respectively. The temperature dependence of the dielectric
constant and the dielectric loss was measured between room temperature and 350°C. With the addition
of Fe2O3, the piezoelectric constant d
33 and electromechanical coupling factor k
p were slightly
decreased, but the mechanical quality factor Q
m was significantly increased. The highest mechanical
quality factor (Q
m=297) was obtained at 0.3 wt% Fe2O3, which is 4.4 times higher than that of
nondoped 0.57PSN–0.43PT ceramics. The P–E and S–E loops of the samples at room temperature and
at 1.0 Hz were measured at the same time using an automated polarization measuring system.
Analysis of Carrier Traps in Si3N4 in Oxide/Nitride/Oxide for Metal/Oxide/Nitride/Oxide/Silicon Nonvolatile Memory
Authors: Aozasa Hiroshi , Fujiwara Ichiro , Komatsu AkihiroNakamura
Published: October 2002

The energy level, density and attempt to escape frequency of
carrier traps in an Si3N4 film in tunnel oxide/nitride/oxide
(ONO) multilayer for metal/oxide/nitride/oxide/silicon (MONOS)
nonvolatile memory are investigated by discharging current transient
spectroscopy (DCTS). To analyze the electrical properties of carrier
traps observed through DCTS, a new model including the tunneling
probability of the tunnel oxide film between the Si3N4 film
and an Si substrate was proposed. As a result, the electron traps in
the Si3N4 film, which are assumed to be related to the
threshold voltage decay, i.e. data retention, were found for the first
time. The energy level of the electron traps in the Si3N4
film in the ONO multilayer was 0.8–0.9 eV from the conduction band
and the density was 1–5×1018 cm-3. The
attempt to escape frequency of 2×1014 s-1 was also
obtained. The energy level of the hole traps and its density were
0.8–0.9 eV from the top of the valence band and 1–4×1018 cm-3, respectively. The magnitude of the trap density obtained from DCTS shows good agreement with that obtained from memory hysteresis characteristics. These results indicate that their carrier traps are amphoteric traps.
Molecular Rotation in an Antiferroelectric Liquid Crystal Studied by 13C-Nuclear Magnetic Resonance Spin-Lattice Relaxation Time Measurement
Authors: Tokumaru Koh , Jin Bo , Yoshida Shohei , Takanishi Yoichi , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo , Nakai Toshihito , Miyajima Seiichi
Published: October 2002

Temperature dependence of the spin-lattice relaxation time T
1 was measured in an antiferroelectric liquid crystal, 4-(1-methylheptyloxycarbonyl) phenyl-4′-octyloxybiphenyl-4-carboxylate (MHPOBC) by means of 13C-nuclear magnetic resonance (NMR). The activation energies determined by the temperature dependence of T
1 are the same for most of the carbon nuclei in the SmA and SmCA
* phases, whereas they are different for carbon nuclei at the chiral center and at the carbonyl carbons. The rotational correlation time changes continuously through the phase change from SmA to SmCA
*. Critical slowing down of the molecular rotatioin was not observed.
Domain Expansion Phenomena in Exchange-Coupled Multilayer Magneto-Optical Films
Authors: Tokunaga Takashi , Fujii Yoshio , Yamada Koichi
Published: October 2002

We investigated the readout signal waveforms from domains recorded with light intensity
modulation in exchange-coupled multilayer magneto-optical (MO) films. It was found that particular
waveforms observed with a steep leading edge were caused by a magnetic domain expansion. When
the recorded domain reached the unstable area where the wall coercivity of the readout layer was
smaller than the readout magnetic field (H
r), it was expanded by an H
r parallel to the magnetization
direction of the readout layer. When the recorded domain entered the unstable area completely, it
shrunk and collapsed. It was considered that the domain expansion and the collapse occurred rapidly,
and produced the rectangular waveforms with steep leading and trailing edges.
A New Type of Light Stabilizer for Dye Layers of Optical Disks: Tetracyanoquinodimethane Derivatives
Authors: Shin-ichi Morishima Shin-ichi Morishima , Koji Wariishi Koji Wariishi , Yoshio Inagaki Yoshio Inagaki , Michihiro Shibata Michihiro Shibata , Toshio Ishida Toshio Ishida , Hiroshi Kubo Hiroshi Kubo
Published: October 2002

A new technology to improve the light fastness of cyanine dye layers of a compact disk recordable (CD-R) or a digital video disk recordable (DVD-R) without using any singlet oxygen quenchers was discussed.
The light fastness of dicarbocyanine dye layers of a CD-R was improved by doping with
tetracyanoquinodimethane (TCNQ) derivatives of various reduction potentials
(E
1/2
RED).
The optimum potential was found to be around 0 V vs saturated calomel electrode (SCE). Doping with TCNQ derivatives was
found to be effective also for the improvement of light fastness of the carbocyanine dye layers which have optical properties suitable
for a DVD-R disk. Excessive electron demanding TCNQ derivatives (E
1/2
RED> 0),
however, showed rather poor jitter and block-error rate (BLER) after exposure to a xenon lamp as compared to a TCNQ derivative (TCNQ1) with an optimal reduction potential (ca. 0 V vs SCE).
Since TCNQ derivatives have no absorption band in a red to near infrared region,
the CD-R or the DVD-R having cyanine dye layers doped with TCNQ derivatives exhibit higher
reflectivity than those with such singlet oxygen quenchers as diimmonium salts.
The Effect of Disc Structure on the Characteristics of the Phase-Change Medium
Authors: Liao Wen-Yih , Lee Sanboh , Huang Der-Ray , Chiang Donyau , Jeng Tzuanren
Published: October 2002

The effects of disc structure on the characteristics of
the phase-change medium are investigated with a tester at the wavelength of 680 nm.
The carrier-to-noise (CNR) and erase ratio depend upon the thickness of
the upper dielectric layer and disc structure of the phase-change media.
CNR exceeds 50 dB when the thickness of the upper dielectric layer is
300 Å–675 Å and erase ratio is above 25 dB when the thickness of the
upper dielectric layer is either 300 Å or 600 Å–700 Å. CNR is 50 dB when
the Al layer is 500 Å–880 Å-thick and erase ratio is 25 dB when the Al
layer is 500 Å–650 Å-thick. The results cannot be explained by optical
simulations. The erase ratio is sensitive to the thickness of the upper
dielectric layer, which is in good agreement with the results of thermal
simulations. It is unfavorable for CNR and erase ratio when the reflective
layer is below 400 Å or above 700 Å. However, some of the structures are
useful for rewritable discs.
Water Absorption and Transient Tilt of Polymeric Substrates for Optical Data Storage Media
Authors: Bruder Friedrich , WilfriedHaese WilfriedHaese
Published: October 2002

A mechanical model for determining water absorption and transient tilt of a
polymeric optical disk is established. Experimental data on disks fabricated from
different substrate materials are in quantitative agreement with the model
predictions. Consequences of transient tilt for the readout signals of future high
density optical data storage media are discussed. Modified polycarbonates with
reduced water absorption can make transient tilt less critical for the readout signal.
This holds true especially in the case of future high-density optical data storage
media.
Time-Dependent Order-Disorder Change in Alloys
Authors: Takao Iwata Takao Iwata
Published: October 2002

The relaxation of order-disorder transition has been
treated. The thermodynamic potential of a non-equilibrium
state is discussed, with the affinity of order-disorder change
being introduced. Entropy production is written in terms
of order parameters. Thus along the line of the
Prigogine-de Groot theory in non-equilibrium thermodynamics,
time variations of order parameters as well as those of entropies
are obtained. It is shown that, in the early stages of both the
formation and decay processes of order at constant temperature,
the short-range order parameter and the amount of produced
entropy vary linearly with time.
Improvement of the Crystalline Quality of InN Layers Grown on Sapphire (0001) by Surface Nitridation
Authors: Tsuchiya Tohru , Yamano Hirofumi , Miki Osamu , Wakahara Akihiro , Yoshida Akira
Published: October 2002

Effect of substrate nitridation on the crystalline quality of InN layers grown
on sapphire (0001) is investigated. The substrate nitridation and the growth of
InN are performed using microwave-excited nitrogen as the reactive nitrogen
source. It is realized that the epitaxial InN layers can be obtained by nitriding
the substrate before the growth and that the crystalline quality of the InN layers
is strongly dependent on the temperature of nitridation. The full-width at half
maximum of x-ray rocking curve for InN (0002) diffraction of 140 arcsec is
achieved by using nitridation.
Derivation of Coupling Coefficients of Modes in Slab Couplers: Ray Theory
Authors: Tseng Shiao-Min , Zhan Jing-Hong , Chen Ding-Yuan
Published: October 2002

From the reflection and transmission of light in coupled slabs, we derive the coupling
coefficient of modes in coupled waveguides. The present result is found to be similar to that
of the conventional coupled-mode theory which requires the evaluation of the overlap integral
of modes in each individual waveguide. Our method is simple, especially for analyzing complicated
coupled waveguides.
Low-energy Ion-scattering Spectroscopic Analysis of Structural Damage in Si Substrate under Ultrathin SiO2 after Gate Etching
Authors: Matsui Miyako , Uchida Fumihiko , Enomoto TakafumiTokunaga , Umezawa Tadashi
Published: October 2002

The relationship between wafer-bias power during over-etching and
structural damage induced in Si(100) substrate under ultrathin SiO2 layers by gate etching was examined by low-energy ion-scattering spectroscopy
(LEIS) and high-resolution X-ray photoelectron spectroscopy. The
crystal structure of the topmost surface of the Si substrate was modified
when the residual SiO2 layer was 2.5 nm thick at a wafer-bias RF power of 70 W during over-etching. This structural damage was shown to be due to
ions coming from plasma irradiation because the residual SiO2 thickness
was close to the projected ion range at an ion energy of 310 eV (which was
estimated from the Vpp of the bias voltage when the RF power was 70 W).
Growth of SiC by Reaction between Thin Films and Ultrafine Particles
Authors: Chihiro Kaito Chihiro Kaito , Seiji Kimura Seiji Kimura , Yuuki Ojima Yuuki Ojima , Yasuyuki Hatayama Yasuyuki Hatayama , Daisuke Ban Daisuke Ban , Toshitaka Nakada Toshitaka Nakada , Yoshio Saito Yoshio Saito , Chiyoe Koike Chiyoe Koike
Published: October 2002

In the case of a reaction between carbon particles and SiO films, silicon carbide was produced by heating above 900°C by the diffusion of Si atoms from Si crystals in SiO films into carbon particles. In the case of that between Si particles and carbon films, silicon carbide was produced above room temperature by the diffusion of carbon atoms into Si particles. In the above two cases, the direction of atom diffusion during the reaction was different.
Low-Pressure Measurement using an Ultrasonic Sensor
Authors: Ishikawa Toshiaki
Published: October 2002

Ultrasonic waves are applied for low-pressure measurement for the first time. The pressure
dependence of ultrasonic signals over the range from 13 to 105 Pa shows a linear relation in a log-log
plot. The linear relation, however, has a bend around 103 Pa which is dependent on the distance
between the speaker and receiver sensors. Ultrasonic signals in the pressure region higher than 103 Pa
are proportional to the pressure p, whereas signals lower than 103 Pa are fitted by a power
function of p
1.5.
New Self-Convergent Programming Method for Multilevel AND Flash Memory
Authors: Yang Evans Ching-Song , Wong Wei-Jer , Wang Yen-Sen , Shen Rick Shih-Jye , Hsu Charles Ching-Hsiang
Published: October 2002

A new self-convergent programming method for multilevel AND-type flash memory is described to accurately control the dispersion of the programmed threshold voltage which is caused by the deviation of the applied voltage or the FN tunneling current.
Both channel initiated secondary electron injection (CHISEL) and avalanche hot electron injection (AHEI) following the edge FN electron ejection can be used as the self-convergent programming techniques.
However, CHISEL is shown to be better than AHEI for self-convergent operation due to faster speed, lower voltage, lower power consumption, and better oxide reliability.
Characteristics of a GaN Metal Semiconductor Field-Effect Transistor Grown on a Sapphire Substrate by Metalorganic Chemical Vapor Deposition
Authors: Egawa Takashi , Nakamura Kouichi , Ishikawa Hiroyasu , Jimbo Takashi , Umeno Masayoshi
Published: October 2002

Electron mobilities of an n-GaN layer on a sapphire substrate
grown by metalorganic chemical vapor deposition were 585 and
1217 cm2/V·s with electron carrier concentrations of
1.1×1017 and 2.4×1016 cm-3 at 300 and
77 K, respectively. A high current level of 281 mA/mm and a large
transconductance (g
m) of 33 mS/mm have been achieved
for a GaN metal semiconductor field-effect transistor (MESFET) with
a gate length of 2 µm and a width of 200 µm at
25°C. The GaN MESFET at high temperature showed degraded
characteristics: low g
m, gate leakage and poor
pinch-off. However, the GaN MESFET at 25°C, measured again
after measurement at 400°C, showed the initial
characteristic in spite of gate leakage. The GaN MESFET exhibited
the sidegating effect, which was thought to be caused by the deep
level in the undoped GaN layer beneath the channel layer. The
uniformity of the sheet resistance seems to be insensitive to the
high dislocation density in the GaN layer.
Improvement of Microwave Performance for Metal-Semiconductor Field Effect Transistors Fabricated on a GaAs/Si Substrate with a Resistive Layer at GaAs–Si Interface
Authors: Aigo Takashi , Fujita Yasuhisa , Tachikawa Akiyoshi , Ohta Yasumitsu
Published: October 2002

We report on the improvement in the microwave performance of metal-semiconductor field effect transistors (MESFETs) fabricated on GaAs/Si
with a resistive layer at the GaAs-Si interface. This layer was obtained
by using a p-type AlGaAs layer or an oxygen-doped AlGaAs layer
grown by metal-organic chemical vapor deposition (MOCVD). Correlation
between sheet carrier concentration in the resistive layer and the device
performance was studied and a marked improvement was found by
reducing the number of carriers in the layer to 4.1×1012 cm-2, which
was about 1/5 of that for standard GaAs/Si. High cutoff frequency of
22 GHz, comparable to that of MESFETs/GaAs, was obtained for
0.8-µm-gate-length MESFETs/Si with a sheet carrier concentration
of 1.5×1012 cm-2. On evaluating scattering parameters for improved MESFETs/Si, it
was found that the parasitic pad capacitance, characteristic for standard
GaAs/Si, became as small as that for MESFETs/GaAs. These results
demonstrate that GaAs/Si with a resistive layer is applicable to GaAs
electronic devices.
Evaluation of True Power Luminous Efficiency from Experimental Luminance Values
Authors: Tsutsui Tetsuo , Yamamato Kounosuke
Published: October 2002

A method for obtaining true external power luminous efficiency
from experimentally obtained luminance in organic light-emitting
diodes (LEDs) was
demonstrated. Conventional two-layer organic LEDs with different electron-transport layer thicknesses were
prepared. Spatial distributions of emission intensities were
observed. The large deviation in both emission spectra and spatial
emission patterns were observed when the electron-transport layer
thickness was varied. The deviation of emission patterns from the
standard Lambertian pattern was found to cause overestimations of
power luminous efficiencies as large as 30%. A method for evaluating
correction factors was proposed.
Optical Performance of the π Cell Compensated with a Negative-Birefringence Film and an A-plate
Authors: Mori Hiroyuki , Bos Philip J.
Published: October 2002

The π cell is known to be a fast and wide-viewing-angle liquid-crystal-display mode due to its unique director configuration. To compensate the viewing angle dependence of the positive birefringence of the π cell, we formulated the idea of using a negative-birefringence structure which has a mirror image of the director configuration of the π cell. Our calculation showed that this combination provides an excellent viewing angle, which was experimentally confirmed by applying a fabricated optical compensation film composed of a discotic layer and an aromatic polyimide layer, both of which have negative birefringence, to a test π cell. An extended Poincaré sphere analysis explained the optical effect of the compensation film and revealed that polarizers are responsible for the low contrast ratio at oblique angles. A complete viewing angle was achieved by adding a positive a-plate which suppresses light leakage at oblique incidence. Color shift upon viewing from oblique angles was also examined. Our experiment showed that the color shift of the π cell is much less than that of the twisted-nematic liquid-crystal display compensated with a similar negative-birefringence film.
Modeling of Tungsten Thermal Chemical Vapor Deposition
Authors: Kim Byunghoon , Akiyama Yasunobu , Imaishi Nobuyuki , Park Heung-Chul
Published: October 2002

Low-pressure chemical vapor deposition (LPCVD) of tungsten (W)
film on silicon (Si) substrate was performed by reducting hexafluoride
(WF6) with hydrogen. This CVD system is known for its nonlinear
dependence of growth rate on WF6 concentration. This study adopted a
simple surface-reaction model which assumes that the precursor, i.e.,
WF6, in the gas phase adsorbs on solid surfaces and then the adsorbed
WF6 molecule is converted into tungsten solid film. The two kinetic
parameters involved in the model are derived from the experimental
results. The solidification rate constant (k
s) is equal to the growth
rate at very high WF6 concentrations. The adsorption rate constant
(k
a) is derived from profile analyses of films grown in microtrenches
under very low WF6 concentrations by applying the conventional Monte
Carlo simulation code, which is valid for linear surface-reaction
systems. In the temperature range of 623 to 823 K, k
a and k
s have
activation energies of 82 kJmol-1, 66.1 kJmol-1, respectively. A newly
proposed Monte Carlo simulation for nonlinear reaction systems, in
combination with the two kinetic parameters, can quantitatively
predict the shape of film in microtrenches for a wide range of
temperatures and WF6 concentrations.
Relationship between a Standing-Wave Field and a Sonoluminescing Field
Authors: Hatanaka Shin-ichi , Tuziuti HidetoMitome , Kuwabara TeruyukiKozuka , Asai Shigeo
Published: October 2002

The relationship between a sound field and a multibubble sonoluminescing field has
been studied experimentally and analytically to clarify the sonochemical reaction field. The
variation of each field in a rectangular glass cell filled with distilled water or a luminol
solution was investigated while changing experimental conditions such as driving frequency,
applied voltage to the transducer, and thickness of the cell bottom. As for the sonoluminescing field,
the intensity of sonoluminescence (SL) was measured and its distribution was observed. As for
the sound field, sound energy density was analyzed theoretically and sound pressure distribution
was observed optically. Comparing them, it became clear that SL occurred at pressure antinodes of
a standing-wave field in the cell. There are upper and lower thresholds of the sound pressure for SL
to occur. This explains the amplitude dependence and spatial
nonuniformity of SL in a standing-wave field.
An Estimation of Continuous Large Strain Distribution Using Complex Discrete Wavelet Transform of 2-Dimensional Speckle Echo Signals
Authors: Kouji Kitamura Kouji Kitamura , Shin-ichi Yagi Shin-ichi Yagi
Published: October 2002

The conventional discrete wavelet transform (DWT) provides a significant
advantage for estimating motion in video signal. In this paper we
describe an adaptation
of a hierarchical region-based matching algorithm by
Magarey and Kingsbury [IEEE Trans. SPSI 46 (1998) 1069] to
complex speckle echo
frame pairs for strain analysis in living tissue.
From the experimental and simulation results,
we verified that the method is useful for quantitative estimation
of displacement and strain of speckle echo signals.
Analysis and Measurement of Reflectance of Moist Sand Surface Using a Four Transmitter Array
Authors: Tao Liang , Fujimoto Masao , Takano Nobuyuki , Motooka Seiichi
Published: October 2002

A one-transmitter eight-receiver (1T8R) array pattern was employed in our previous
work to measure the moisture content of sand by neural-network data processing of ultrasonic
pulse-echo signals. In order to enhance the power of the incident wave to improve the stability
of measurement of sand moisture, this paper proposes a four-transmitter five-receiver (4T5R)
array pattern. The results of theoretical estimation and experimental measurement show a
similar tendency, that the reflectance of 4T5R is markedly larger than that of 1T8R. Thus it is
verified that the new transmitter-receiver arrangement improves the measuring stability.
Preliminary Experimental Study for Surface Plasmon Thermal Wave Microscopy
Authors: Tokunaga Yoshiaki , Minamide Tsuyoshi Nakai andAkiyuki
Published: October 2002

A Preliminary experiment for surface plasmon thermal wave
microscopy (SPTWM) is reported. This is a new technique of
nondestructive evaluation of thin films using thermal waves excited by
energy conversion due to electron-phonon interaction with nonradiative surface plasmon.
Detecting Spurious Modes in Quartz Plates by Measuring Surface Charges
Authors: Watanabe Yasuaki , Tanaka Tomohiko , Goka Shigeyoshi , Sekimoto Hitoshi
Published: October 2002

In this paper, we describe a method for detecting weak spurious modes in quartz plates. This method picks up the weak modes by measuring the frequency characteristics of high-frequency charge voltages, which are excited at resonant frequencies, at many points on the plate surface. The measured results for two strip AT-cut quartz resonators show that this method can detect very small resonance modes undetectable by conventional methods.
Basic Consideration of Trident-Type Tuning Fork Accelerometers Using Coriolis Force Phenomenon
Authors: andYoshiro Tomikawa Norikazu Ishida
Published: October 2002

In this paper we deal with a new type of accelerometer using the Coriolis force phenomenon.
This accelerometer, which consists of a trident-type tuning fork resonator, is driven and its signal is detected by piezoelectric ceramics.
In this study, two kinds of accelerometers are investigated. First, the construction and operating principle of the accelerometers proposed by us are described and, next, the experimental results of prototype accelerometers are presented. The results prove that the prototypes can basically operate as accelerometers.
Properties of Leaky, Leaky Pseudo, and Rayleigh Surface Acoustic Waves on Various Rotated Y-cut Langasite Crystal Substrates
Authors: Michio Kadota Michio Kadota , Jun Nakanishi Jun Nakanishi , Takeshi Kitamura Takeshi Kitamura , Makoto Kumatoriya Makoto Kumatoriya
Published: October 2002

A leaky surface acoustic wave (LSAW) and a leaky pseudo SAW (LPSAW) of
various rotated Y-cut langasite substrates grown by the Czochralski method
were measured by an ultrasonic microscope. The measured results agreed well
with the values calculated using Ilyaeve's material constants of five kinds
of material. Rayleigh SAW transversal filters, having various aluminum (Al)
thicknesses of interdigital transducers (IDT), were constituted on
(0°, 140–150°, 24–25°) and
(12°, 150–153°, 36–37°) plates.
A temperature coefficient of frequency (TCF) of the Rayleigh SAW filters
was measured by measuring their center frequency.
It was clarified that (0°, 142°, 24.5°)
and (0°, 143°, 24°) plates at
normalized Al-IDT thickness (H
A
l
/λ) 0.0125, and
(12°, 153°, 37°) plates
at H
A
l
/λ = 0.0625 showed turnover temperatures of
25°C, 30°C and 28°C
and excellent TCFs (ΔF/F/°C = 1.83, 1.63,
and 1.95 ppm/°C).
Measured results of electromechanical coupling factor on their substrates
showed similar values (k

s

2 = 0.41, 0.42 and 0.46%) to
the theoretical ones. The
(12°, 153°, 37°) plate having the
largest coupling factor is the most suitable one for SAW devices.
Furthermore, the velocity, the coupling factor,
and the propagation loss of LSAW on air/various Y-X langasite
plates (0°, θ, 0°) were also calculated.
Polynomial Approximation of SAW Reflection Characteristics for Fast Device Simulation Tools
Authors: Koji Ibata Koji Ibata , Tatsuya Omori Tatsuya Omori , Ken-ya Hashimoto Ken-ya Hashimoto , Masatsune Yamaguchi Masatsune Yamaguchi
Published: October 2002

The paper deals with the derivation of simple polynomials characterising
surface acoustic wave (SAW) reflection by metallic gratings
with various widths and thicknesses.
Such polynomial approximation makes it possible to estimate coupling of mode
(COM) parameters
in markedly reduced computational time. For very sophisticated SAW devices,
this is of great use to develop high-speed simulation and design tools
based on the COM method.
In the present study,
it is shown how simply and accurately
the SAW reflection by aluminium gratings
on 128°YX-LiNbO3 substrates or 36°YX-LiTaO3 substrates is characterised by polynomial approximation.
Operating Characteristics of a Same-Phase Drive-Type Ultrasonic Motor Using a Flexural Disk Vibrator
Authors: Takano Takehiro , Tomikawa Yoshiro , Kusakabe Chiharu
Published: October 2002

In this paper we describe an ultrasonic motor using a flexural disk
vibrating in two degeneration modes driven by a same-phase input signal.
Its operating characteristics depend considerably on the pressing force
between the stator and the rotor. We report some experimental studies of
this effect. Measurements of the vibration mode showed that the change in
the rotational direction of the motor was caused by a shift in the vibration
axis of the mode synthesized from two degeneration modes. It is also shown
that the motor's operating characteristics can be adjusted via an electrical
element connected to the control terminal.
The Suppression of Mechanical Resonances of LiNbO3 Actuator with Oppositely-Polarized Layers
Authors: Yokoyama Hideki , Kudo Subaru , Wakatsuki Noboru
Published: October 2002

A LiNbO3 bimorph actuator can be fabricated on a single crystal plate with inverse polarized layers. The actuator shows no hysteresis and no creep. However, as a thin rectangular plate it inevitably exhibits mechanical high Q resonance. In this paper, we propose and examine a new servo-actuator with an integrated displacement velocity sensor and a feedback circuit to suppress resonance. Using a finite element method (FEM), the driving electrode was designed to drive only the first resonant mode and to suppress the second mode.
We experimentally confirmed that the electromechanical coupling of a
driving electrode to the secondary mode was negligible. Therefore, we
applied the negative feedback circuit for the servo-actuator. Optical
measurement of the displacement of the actuator confirmed no ringing
response to step impulse driving voltage.
Hall Effect Measurements of Surface Conductive Layer on Undoped Diamond Films in NO2 and NH3 Atmospheres
Authors: Gi Ri , Tashiro Kazuhiro , Tanaka Seiichi , Fujisawa Takao , Kimura Hideki , Kurosu Tateki , Iida Masamori
Published: October 2002

In order to clarify the mechanism of change in resistance of the surface conductive
layer exposed to oxidizing and reducing gases, the Hall effect measurements
of the surface conductive layer on as-grown undoped diamond films
in NO2 and NH3 gas atmospheres were carried out.
It was found that holes were generated in the surface conductive layer
by the adsorption of NO2 gas, and the adsorption of NH3 gas
resulted in the disappearance of the holes. Morever, the dependences of gas
concentration on the sheet resistivity, carrier density per unit area and Hall mobility
were observed. The mechanism of change in resistance of the surface conductive
layer in gas atmospheres could be explained by the proposed model based
on the experimental results.
Electric Properties of Zinc Oxide Epitaxial Films Grown by Ion-Beam Sputtering with Oxygen-Radical Irradiation
Authors: Tsurumi Takaaki , Nishizawa Shuichi , Ohashi Naoki , Ohgaki Takeshi
Published: October 2002

Undoped and aluminum-doped ZnO epitaxial films were grown on (001) sapphire substrates by an ion-beam sputtering method with or without the irradiation of oxygen radicals. The effect of oxygen-radical irradiation was notable in the undoped ZnO films when the growth temperature was relatively low. The irradiation improved the crystallinity and decreased the oxygen-vacancy concentration, while it induced internal stress into the films. The carrier concentration of the undoped ZnO films was decreased by the oxygen-radical irradiation, which was attributable to a decrease in the oxygen-vacancy concentration. The Hall mobility of the undoped ZnO films was as low as 1–3 cm2 V-1 s-1. The low mobility was explained by carrier scattering due to the potential barriers at the grain boundaries. The height of the potential barriers at the grain boundaries decreased with increasing carrier concentration. This behavior was well explained by a simple model assuming a single defect state at grain boundaries.
Enhancement of Electron Emission Characteristics of Platform-shaped Mo Emitters by Diamond-like Carbon Coatings
Authors: Lin Chin-Maw , Chang Shoou-Jinn , Yokoyama Meiso , Lin I-Nan , Chuang Feng-Yu , Tsai Chun-Hui , Wang Wen-Chun
Published: October 2002

The effect of diamond-like carbon (DLC) films coated by the
pulsed laser deposition technique on the electron field emission
characteristics of platform-shaped Mo emitters was investigated. It
was observed that DLC coatings can significantly enhance electron
emission. The gate-to-cathode operating voltage (for an anode current
density of 1 mA/cm2) was lowered from 50 V for uncoated
platform-shaped Mo emitters to 20 V for DLC-coated platform-shaped Mo
emitters. The lifetime of the DLC-coated emitters is at least twice
that of the uncoated ones. Moreover, the DLC-coated platform-shaped Mo
emitters exhibited durability superior to that of the DLC-coated
Spindt-type emitters, which was due to the abundance of emission sites
in the platform-shaped
Mo emitters.
Space-Correlation Analysis of Formate Ions Adsorbed on TiO2(110)
Authors: Onishi Hiroshi , Fukui Ken-ichi , Iwasawa Yasuhiro
Published: October 2002

The ability of the space-correlation analysis of scanning tunneling microscope (STM) image to deduce short-range order is demonstrated on a dilute formate ion (HCOO-) overlayer prepared on a TiO2(110) surface. A c(4×2) local order of formate ions is found at 22% of the saturation coverage, whereas the known (2×1) long-range order develops over the surface of the complete saturation coverage. The c(4×2) order is interpreted as a structure where electrostatic repulsion between formate ions is minimized. The c(4×2) order does not develop on the surface when formate coverage is increased, probably due to the formation of formate-hydroxyl-formate chains on the surface.
Si(111) Surface under Phase Transitions Studied by the Analysis of Inner Layer Structures Using Bias-Dependent Scanning Tunneling Microscopy
Authors: Li Koji Miyake , Haruhiro Oigawa Haruhiro Oigawa , Hidemi Shigekawa Hidemi Shigekawa
Published: October 2002

In both cases of quenched and HBO2-molecule-irradiated Si(111) surfaces, corner holes are observed to exist along the boundaries between 7×7 and disordered structural domains. From the analysis of the bias-dependent STM images, it was found that the corner holes included complete stacking fault and dimer structures in the second layer, i.e., a complete corner hole. This result strongly indicates that the complete corner holes play important roles in both the formation and stabilization processes of the dimer-adatom-stacking fault (DAS) structure. In addition, the formation of a structure similar to that of the corner hole was often observed at the boundaries of three out-of-phase c(2×8) structural domains in quenched surfaces, which may result in nucleuses for the formation of the complete corner hole.