bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition of SiO2 Thin Films by Combined Low-Energy Ion-Beam and Molecular-Beam Epitaxial Method
Authors: Shibata Hajime , Kimura Shinji , Takatoh Hidetaka
Published: October 2002

A combined ion-beam and molecular-beam epitaxial (CIBMBE) method
was applied for the deposition of SiO2 thin films using a
mass-separated low-energy (50 eV) O+ ion-beam and a Si
molecular-beam. From X-ray photoelectron spectra, it was confirmed
that stoichiometric SiO2 thin films were successfully formed, and
it was suggested that the chemical state of the Si atoms in the
SiO2 layers is identical (Si4+) to that in the films formed
by the thermal oxidation of Si. It was suggested that the CIBMBE is a
versatile technique for the deposition of SiO2 thin films whose
quality is comparable to that of the films formed by the thermal
oxidation method.
Gap Length Dependence of Electron Energy Distribution in Low-Pressure Ar Capacitively Coupled RF Discharges
Authors: Takashi Kimura Takashi Kimura , Kouji Kaga Kouji Kaga , Kazuyuki Ohe Kazuyuki Ohe
Published: October 2002

The electron energy distribution function (EEDF) at the midplane was measured using a Langmuir probe in symmetrically capacitively coupled RF (13.56 MHz) Ar discharges by changing the gap length from 2 cm to 10 cm over the pressure range from 0.03 Torr to 0.1 Torr, while keeping the RF current constant at 140 mArms. The EEDFs measured at pressure lower than 0.05 Torr formed a bi-Maxwellian distribution over the measured gap length. On the other hand, the EEDF structure measured at pressure higher than 0.07 Torr changed from bi-Maxwellian to Maxwellian, and to Druyvesteyn distributions with increasing gap length. The gap length dependence of the EEDF structure in the high-energy region can be explained by the transition from the stochastic to the joule heating, while that in the low-energy region can be explained by comparing the elastic collision frequency and the e-e Coulomb collision frequency.
Microwave Properties of (Ba1-xSrx)Sm2Ti4O12 Ceramics and Its Application in Dielectric Resonator Antenna
Authors: Yang Cheng-Fu
Published: October 2002

In the (Ba1-x
Sr
x
)Sm2Ti4O12
(BSST, 0≦x≦0.1) system SrO is used to substitute BaO to improve the
microwave dielectric properties of BSST ceramics. As the amount of SrO increases
from 0 to 0.06 mol%, the dielectric constant (ε
r) of BSST
ceramics decreases from 82.3 to 72.3 and the temperature coefficients of the resonant
frequency (τf) change from -21.1 to -2.36 ppm/°C, but the
quality values (Q
*
f) show no apparent change with the variation of the x
value. In the BSST system, the (Ba0.98Sr0.02)Sm2Ti4O12
ceramic reveals the maximum Q
*
f value. With the loading of a
(Ba0.98Sr0.02)Sm2Ti4O12 dielectric resonator (DR), a
circular polarization (CP) design of a DR antenna is fabricated through crossed slot of
unequal arm lengths in the ground plane of a microstrip line. The proposed CP design
results in the excitation of two near-degenerate orthogonal modes of near-equal
amplitudes and a 90° phase difference. For the proposed design applied to the
low-profile square-cross-section DR antenna of very high permittivity studied here, a
large CP bandwidth, determined from the 3 dB axial ratio of as high as 2.39%, is also
obtained.
Development of Optical Pickup for Digital Versatile Disc Using Two-Wavelength-Integrated Laser Diode
Authors: Uchiyama Mineharu , Ebihara Takeshi , Omi Kunio , Kitano Hisashi , Hoshino Isao , Mori Kazushige
Published: October 2002

A digital versatile disc (DVD)-and compact disc (CD)-compatible
optical pickup using a two-wavelength-integrated laser diode
(TWIN-LD) has been developed. The TWIN-LD has two emission points in
one chip, one for the red laser beam to read out signals from DVDs
and the other for the IR laser beam to read out signals from CDs
that are arranged along the active layer. With the application of a
TWIN-LD to the optical pickup, the necessity for four optical
components, namely, a laser diode, photodetector, holographic
optical element and dichroic prism, is avoided in comparison with
conventional optical pickups. This paper discusses some key points
for designing an optical system using a TWIN-LD, and the results of
the experiments appling the optical system to an optical pickup
7.3 mm in height.
Accurate Estimation of Aberrations of Microoptics Components through Intensity Measurements: Numerical Simulations for Best Positioning and Noise Analysis
Authors: Marcos Soto Marcos Soto , Susana Ríos Susana Ríos , Eva Acosta Eva Acosta , Valerii Voitsekhovich Valerii Voitsekhovich
Published: October 2002

In this work we analyse the accuracy in the estimation of aberrations of microoptics components through intensity measurements by means of the transport of intensity equation (TIE) retrieval scheme. Through results of numerical simulations, the position of the measurement planes of transverse irradiance as well as the separation between them is optimised in order to minimise peak to valley values of the difference between the input wavefront and the retrieved one. Random gaussian noise with zero mean is included in the calculations.
Properties of Substrate Phonon Events in Superconducting Tunnel Junctions Induced by X-Ray Absorption
Authors: Chiko Otani Chiko Otani , Tokihiro Ikeda Tokihiro Ikeda , Hiroshi Kato Hiroshi Kato , Kazuhiko Kawai Kazuhiko Kawai , Hiromasa Miyasaka Hiromasa Miyasaka , Takayuki Oku Takayuki Oku , Wataru Ootani Wataru Ootani , Hiromi Sato Hiromi Sato , Hirohiko M. Shimizu Hirohiko M. Shimizu , Yoshiyuki Takizawa Yoshiyuki Takizawa , Hiroshi Watanabe Hiroshi Watanabe , Hiroshi Nakagawa Hiroshi Nakagawa , Hiroshi Akoh Hiroshi Akoh , Masahiro Aoyagi Masahiro Aoyagi , Tohru Taino Tohru Taino
Published: October 2002

The spectra of substrate phonon events induced by illuminating with X-rays obtained with Nb-based superconducting tunnel junctions (STJs) fabricated on a sapphire substrate were examined. We constructed a geometrical model in which the collection efficiency of phonons is proportional to the solid angle subtended to the STJ from the position of the absorption. By using the Monte-Carlo simulation, we succeeded in fairly reproducing the features of the spectra obtained by our measurements. A comparison of the model spectra with the measured ones revealed that a mismatch of the acoustic impedance at the junction-substrate interface and the spatial spread of a phonon cloud play an important role in the determination of the spectra. By including these effects, we show that the measured spectra can be well reproduced by adjusting only one free parameter, the radius of the phonon cloud. We estimated this radius in a sapphire substrate to be ∼20 µm under 5.9 keV X-ray illumination.
Low-Temperature and High-Rate Deposition of SrTiO3 Thin Films by RF Magnetron Sputtering
Authors: Kohara Naoki , Yoshida Akihisa , Sawada Taisuke , Kitagawa Masatoshi
Published: October 2002

SrTiO3 thin films have been prepared by RF magnetron sputtering at the a substrate
temperature of 200°C and a high deposition rate of 35 nm/min on Al/glass substrates. The
deposition rate of the SrTiO3 thin film was controlled by RF power during the deposition. The
orientation of the films changed and the grain boundaries became sparse with increasing RF power.
Furthermore, the leakage current of the capacitors also increased with increasing RF power. As the
RF power increased, the signal intensity ratios of O2
+/O and Ti/Sr in the optical emission spectroscopy
decreased. The application of optimum working pressure resulted in recovery of the signal intensity
ratios of O2
+/O in the optical emission spectroscopy and improvement in the properties of the SrTiO3
film deposited at a high RF power. The SrTiO3 film of 300 nm thickness exhibited a relative dielectric
constant of 64 and a leakage current of 4×10-10 A/cm2
at the voltage of +3 V.
Improved Theory for Carrier Leakage and Diffusion in Multiquantum-well Semiconductor Lasers
Authors: Irikawa Michinori , Ishikawa Takuya , Fukushima Toru , Shimizu Hitoshi , Kasukawa Akihiko , Iga Kenichi
Published: October 2002

A model of carrier leakage lifetime is presented taking into account the density
of states for quantum-wells and band nonparabolicity. Rate equations are also proposed
including leakage of both types of carriers and carrier loss in both sides of optical
confinement layers. The carrier loss coefficients extracted by adopting this model on
the measured modulation bandwidth of 1.5 µm-wavelength multiquantum-well
lasers coincided with reported values within their distributions. Measured temperature
sensitivity of threshold current and that of K factor were also well explained with
the improved model using those extracted carrier loss coefficients. The dominant
causes of low characteristic temperature T
0 of present compressive-strained
multiquantum-well lasers were quantitatively considered and found to be attributed to
1) Auger carrier loss and 2) thermionic carrier leakage and diffusion delay effect.
T
0 over 150 K is expected by reducing the effect of those two factors.
Possibilities of finding an actual method to reduce the effect of the above two factors
are discussed.
An Improved Azimuthal Anchoring Energy Measurement Method Using Liquid Crystals with Different Chiralities
Authors: Yukito Saitoh Yukito Saitoh , Alan Lien Alan Lien
Published: October 2002

An improved method for measuring the azimuthal anchoring energy of liquid crystals has been developed. Without knowing the easy axes of the cells precisely, it is possible to measure their anchoring energy precisely, using the same liquid crystals but with different chiralities for the divided cells. The principles and measurements are discussed.
Twisted-Film Compensated Twist Nematic and Double Twist Nematic Modes for Achromatic Reflective Displays
Authors: Lu Minhua , Yang K. H. , Rosenbluth Alan E. , Nakasogi Teruhiro
Published: October 2002

For reflective liquid crystal displays, we report a band-shifted
double twist nematic (BSDTN) mode that have advantages of achromatic
spectral response, wider viewing angle, and faster switching than
regular uncompensated normally-black twist nematic
modes. Experimental results on a band-shifted twisted-film
compensated twist nematic (BSTFTN) mode whose display qualities are
similar to those of BSDTN are also presented. We believe that BSTFTN
can be mass-produced with high yield and low cost. Both BSDTN and
BSTFTN are suitable for Si-wafer based reflective light valves for
projection and virtual display applications.
Absorption Anisotropy for Lattice Matched GaAs/AlGaAs Multiple Quantum Well Structures under External Anisotropic Biaxial Strain: Compression along [110] and Tension along [1̄10]
Authors: Man-Fang Huang Man-Fang Huang , Elsa Garmire Elsa Garmire , Yen-Kuang Kuo Yen-Kuang Kuo
Published: October 2002

We report theoretical studies on the optical absorption anisotropy for excitonic transitions in lattice-matched GaAs/AlGaAs multiple quantum well (MQW) structures under simultaneous compression and tension applied along the [110] and
[1̄10] directions of the MQW, respectively. The analyses are based on a model that includes both the
4×4 k·p Hamiltonian and the strain Hamiltonian. The wave functions, found by solving the eigenvalue equations, are used to calculate the dipole matrix elements for excitonic transitions and evaluate the anisotropic absorption properties. The effect of variation of parameters such as well width and barrier height on the performance of the strained GaAs/AlGaAs MQW electroabsorption modulators is discussed.
Effect of Carrier Localization on Optical Gain Formation in CdxZn1-xS/ZnS Quantum Wells
Authors: Onodera Chikara , Taguchi Tsunemasa
Published: October 2002

We present a theoretical study on optical gain formation due to the localized
state in Cd
x
Zn1-x
S/ZnS strained-layer quantum wells. We have calculated
the optical gain coefficient, which is produced when carriers are localized in a quantum
disk due to potential fluctuation of the alloy in a Cd
x
Zn1-x
S well. It is
assumed in our model that the density of the localized state in this quantum disk can be
followed by Gaussian distribution function. It has been revealed that the formation of
optical gain due to the localization of carriers takes place at a carrier concentration of
about 1×1018 cm-3, which is one order of magnitude lower than that of
band-to-band transition.
Microstructural and Electrical Properties of BaxSr1-xTiO3 Thin Films on Various Electrodes
Authors: Kyung Kim Seokmin Hong
Published: October 2002

BaxSr1-x
TiO3 (BST) thin films were deposited simultaneously on various electrodes by the sputtering technique. When the substrate temperature was varied, the BST thin film on each electrode showed good crystallinity above 550°C as revealed by X-ray diffraction measurements. The surface morphology, determined by atomic force microscopy, indicated that the roughness of BST thin films on RuO2 was substrate dependent. However, BST thin films on Ru electrodes are smoother and showed no substrate dependence, probably because the precursor surface diffusion length was greater than the sinusoidal perturbations of the wavelength. From the stoichiometry analysis of the BST thin films, the largest dielectric constant was obtained at around a 0.7 molar ratio of Ba in each electrode. BST thin film on Pt/TiN/SiO2/Si showed the highest dielectric constant and the lowest leakage current among the considered samples, displaying great improvement over the thin film deposited onto Pt/SiO2/Si by insertion of a TiN barrier layer. The electrical properties of BST thin films on RuO2 were poorer than those of BST thin films on Ru, mainly because of the rough morphology originating from the rough surface of the bottom electrode.
Space Charge Distribution and Capacitance–Voltage Characteristics of Metal/Polyimide Langmuir-Blodgett Film/Metal Structure
Authors: Li Cheng-Quan , Wu Chen-Xu , Iwamoto Mitsumasa
Published: October 2002

The capacitance–voltage (C–V) characteristics of the metal/polyimide (PI) Langmuir-Blodgett (LB) film/metal structure are analyzed, taking into account the interfacial electrostatic phenomena and the presence of the interfacial electronic states. The capacitance (C) and the additional relative capacitance [(C-C
0)/C
0] at various applied external voltages (V
ex) are calculated, under the assumption that the electron acceptor density of states (DOS) at the interfaces has a Gaussian profile centered at the energy level of the lowest unoccupied molecular orbitals (LUMO). The results reveal that when a positive bias (V
ex>0) is applied to a metal/insulator (PI LB film)/metal (MIM) element, the capacitance and the additional relative capacitance decrease as the thickness of PI LB film increases, while a negative bias (V
ex<0) gives rise to slight changes of the capacitance and the additional relative capacitance. In addition, it is found that the density of space charge also experiences slight changes as the applied external bias increases. The calculated results of the C–V characteristics of the MIM element show good agreement with the experimental results.
Base Sequence Dependence of Deoxyribonucleic Acid Studied by Scanning Tunneling Microscopy
Authors: Kanno Takashi , Tanaka Hiroyuki , Miyoshi Norio , Fukuda Masaru , Kawai Tomoji
Published: October 2002

In order to identify high-order structures and pitch length of deoxyribonucleic
acid (DNA), poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) were
adsorbed on Cu(111) substrates by the pulse injection method and were observed by
ultra high vacuum (UHV) scanning tunneling microscopy (STM). In large-scale STM
images, the high-order structure of poly(dG-dC)·poly(dG-dC) has a higher
divergence and shorter dimension compared with those of
poly(dA-dT)·poly(dA-dT). High-resolution STM images revealed that the pitch
lengths of poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) adsorbed
onto the surface were longer than those possessed in the aqueous solution.
Measurement of Thermal Diffusivity of Multilayer Optical Thin Film Systems Using Photoacoustic Effect
Authors: Kwon Kyong Up , Choi Moon Ho , Kim Sok Won , Seong Dae Jin , Kim Jong Chul
Published: October 2002

In other to develop ultrahigh-power laser systems, laser mirrors
must be highly resistant to thermal shock and effectively cooled;
therefore, the study of optical multilayer systems which have high
thermal diffusivity has become important. In this study, we designed
and developed two-layer antireflection (AR) optical coating samples
and five-layer high-reflection (HR) optical coating samples on glass
substrate under different evaporation conditions of coating speed (10,
20 Å/s) and substrate temperature (50, 100, 150, 200°C),
using two dielectric materials MgF2 and ZnS which have different
refractive indices, and the through-plane thermal diffusivity was
measured using the photoacoustic effect. The thermal diffusivities of
the samples were obtained from the measured photoacoustic signals by
changing the modulation frequency of the Ar+ laser beam. The
results indicated that the thermal diffusivity is maximum when the
coating speed is 10 Å/s and substrate temperature is 150°C,
and is closely related to the morphology of the films.
Improvement of Memory Characteristics of Metal-Ferroelectrics/Insulating Buffer Layer/ Semiconductor Structures by Combination of Pulsed Laser Deposited SrBi2Ta2O9 Films and Ultra-Thin SiN Buffer Layers
Authors: Yamaguchi Takeshi , Koyama Masato , Takashima Akira , Takagi Shin-ichi
Published: October 2002

For the realization of good memory characteristics,
metal/ferroelectrics/insulating buffer layer/semiconductor-field effect transistor
(MFIS-FETs), suppression of the interfacial reaction between ferroelectrics and
semiconductors, and a higher capacitance for the buffer layer are required. In order to
satisfy the above requirements, optimization of the buffer layer structure in the MFIS
structure is performed. SrBi2Ta2O9(SBT) films deposited by the pulsed
laser deposition (PLD) technique without applying any high-temperature processes are
combined with ultra-thin SiN films, for the first time. It is found that the SiN buffer
layer is maintained as thin as 2 nm with the suppression of interfacial reactions even
after the deposition of SBT films. As a result, the memory characteristics are
significantly improved. The memory window size on the C–V curve is as large as
8 V at the gate voltage sweep width of ΔV
g=14 V. The measured
retention time of the Al/SBT/SiN/Si capacitor is longer than that of the
Al/SBT/SiO2/Si capacitor by two orders of magnitude. These improvements are
attributable to the higher capacitance and high immunity for the interface reactions
provided by the ultra-thin SiN buffer layer.
Low Temperature Recovery of Ru/(Ba, Sr)TiO3/Ru Capacitors Degraded by Forming Gas Annealing
Authors: Iizuka Toshihiro , Arita Koji , Yamamoto Ichiro , Yamamichi Shintaro , Yamaguchi Hiromu , Matsuki Takeo , Sone Shuji , Yabuta Hisato , Miyasaka Yoichi , Kato Yoshitake
Published: October 2002

A low temperature N2 post-annealing process was proposed to
improve the degradation of Ru/(Ba, Sr)TiO3/Ru capacitors due to
forming gas annealing. After N2 post-annealing at 300°C,
the leakage current degraded by forming gas annealing was completely
recovered to the initial level without affecting the SiO2
equivalent thickness of 0.51 nm. No degradation of the subthreshold
characteristics of n-channel metal-oxide-semiconductor field effect
transistors and N+P junction leakage current by the
post-annealing was also confirmed. The Ru/(Ba, Sr)TiO3/Ru
capacitor technology with this post-annealing process is suitable
for dynamic random access memories in 0.13 µm generation and
beyond.
Growth of Epitaxial SrBi2Ta2O9 Thin Films by Metalorganic Chemical Vapor Deposition
Authors: Ishikawa Katsuyuki , Saiki Atsushi , Funakubo Hiroshi
Published: October 2002

Epitaxially grown SrBi2Ta2O9(SBT) thin films were deposited on
various types of substrates at temperatures ranging from 620 to 910°C by
metalorganic chemical vapor deposition. Epitaxial SBT films with (001) orientation
were easily grown on perovskite- and rocksalt-structured substrates. The films tended
to grow at lower deposition temperatures on the substrates, which had a lower
mismatch with the film. When the film was deposited on a fluorite-structured
substrate, yttria-stabilized zirconia (YSZ), it had a fluorite phase at a wide deposition
temperature range. Epitaxially grown SBT film with (116) orientation was prepared on
(110) SrTiO3 substrate at 820°C. This film exhibited twinning.
Improved Metal Gate Process by Simultaneous Gate-Oxide Nitridation during W/WNx Gate Formation
Authors: Moriwaki Masaru , Yamada Takayuki , Harada Yoshinao , Fujii Shinji , Yamanaka Michinari , Shibata Jun , Mori Yoshihiro
Published: October 2002

The improvement of gate dielectric reliability by simultaneous gate dielectric
nitridation during W/WN
x
gate sputtering deposition was investigated. The time-to-breakdown (t
bd) of the W/WN
x
gate metal-oxide-semiconductor (MOS) capacitor was improved compared to that of the W gate by increasing the N2 flow ratio (R
N) during the reactive sputtering deposition of the WN
x
gate with an N2–Ar gas mixture. The surface nitridation of the gate dielectric of the W/WN
x
gate MOS capacitor was confirmed to occur simultaneously with the reactive sputtering
deposition of the WN
x
layer. The improvement of the gate dielectric reliability was
achieved by the nitridation, which terminated the dangling bonds formed in the gate
dielectric surface during the metal gate sputtering process. Other characteristics of
the W/WN
x
gate electrode were also demonstrated. The W/WN
x
gate provides low resistivity, a near-mid-gap work function and a good gate etch profile.
Photoluminescence of Low-Energy B+-Implanted Silicon under Ultraviolet Light Excitation
Authors: Terashima Koichi , Miyoshi Kousuke , Tajima Michio
Published: October 2002

We measured photoluminescence (PL) spectra of Si implanted with
0.5 keV B+ ions to doses varying from 1.0×1014 to
4.0×1015 cm-2. We
compared the PL spectra under ultraviolet (UV) light (the 351 and
364 nm lines of an Ar ion laser) excitation with those under visible
light (the 488 nm line of an Ar ion laser) excitation. The emission
due to the impurity band of B was observed only in the case of the
UV light excitation, indicating that the activated B atoms were
located in the shallow region of the order of 10 nm. The I1 line at
1.02 eV and the broad band consisting of two bands with peaks at
0.82 and 0.97 eV were also observed in the PL spectra. They are
related to different types of point defect clusters. Comparing the
PL spectra under different light excitations, we conclude that the
distribution of the defects induced by ion implantation is not
restricted in the shallow region of the implanted B atoms even in
the as-implanted sample. We also conclude that the 0.97 eV defect
extends to the region deeper than the region of the 0.82 eV defect
after the annealing.
New Nonvolatile Analog Memories for Analog Data Processing
Authors: Tomochika Harada Tomochika Harada , Atsushi Sato Atsushi Sato , Mitsunaga Kinjo Mitsunaga Kinjo , Yasuhiro Katayama Yasuhiro Katayama , Shigeo Sato Shigeo Sato , Koji Nakajima Koji Nakajima
Published: October 2002

For the purpose of realizing a new intelligent system using mixed signal
technology and its simplified VLSI implementation,
we develop two new nonvolatile analog memories
called “DTSDAM (dual tunnel SDAM)”
and “FBSDAM (SDAM with feedback circuit)”
based on “SDAM (switched diffusion analog memory)”.
We fabricate these two analog memories using the 4 µm
double-poly double-metal silicon technology developed
for nonvolatile analog memories.
We report the measurement results for the fabricated chips
and estimate the performance of these new analog memories.
Nitridation of GaP (100) Surfaces by rf Nitrogen Radicals and by Electron Cyclotron Resonance Nitrogen Plasma
Authors: Ootomo Shin-ya , Hashizume Tamotsu , Hasegawa Hideki
Published: October 2002

The nitridation process of a GaP (100) surface using rf nitrogen radicals
and electron cyclotron resonance (ECR) N2 plasma at 400–500°C has been investigated
by reflection high-energy electron diffraction (RHEED), in situ X-ray photoemission
spectroscopy (XPS), atomic force microscopy (AFM) and
cathodoluminescence (CL) methods. The P-stabilized (2×4) surface prepared by ultra high-vacuum (UHV) thermal cleaning was
used as an initial surface. At the initial stage of nitridation, both the P–N and
Ga–N components were formed on the GaP surface. The subsequent radical process led to
the dominant formation of strained small granular grains of cubic GaN with diameters
of 5–10 nm. Further nitridation produced much larger hemispherical GaN grains.
The surface exposed to ECR N2 plasma for 60 min exhibited an anisotropic surface
morphology with rectangular structures which aligned to the [011] direction. Clear
CL peaks originating from the cubic GaN structure were observed on
these nitrided surfaces.
Comparison of Optical Properties of GaN/AlGaN and InGaN/AlGaN Single Quantum Wells
Authors: Chichibu Shigefusa F. , Shikanai Amane , Deguchi Takahiro , Setoguchi Akiko , Nakai Rikuro , Nakanishi Hisayuki , Wada Kazumi , DenBaars Steven P. , Sota Takayuki , Nakamura Shuji
Published: October 2002

Static, field-modulated and time-resolved spectroscopies were carried out to compare the electronic states between GaN/AlGaN binary and InGaN/AlGaN ternary single quantum wells (SQWs).
The internal field that exists across the quantum well (QW) naturally induces a quantum-confined Stark effect (QCSE), namely the redshift of the QW resonance energy and decrease of the electron-hole wavefunction overlap.
The GaN/AlGaN SQW exhibited a weak emission due to QCSE. However, optical absorption and degenerate pump-probe measurements revealed that excitonic character was maintained for thin QWs with the well width nearly the same as the bulk free exciton Bohr radius even under an electric field as high as 0.73 MV/cm.
A slightly In-alloyed InGaN SQW exhibited a bright luminescence peak in spite of an effective bandgap inhomogeneity in the QW, which was confirmed by the point excitation and monochromatic cathodoluminescence (CL) mapping method.
The lateral interval of each light-emitting area was estimated from the spatial resolution of the CL mapping to be smaller than 60 nm. Such local potential minima is considered to be formed due to the presence of a structure similar to quantum-disks [M. Sugawara: Phys. Rev. B 51 (1995) 10743].
Carriers generated in the InGaN QWs are effectively localized in these regions to form localized QW excitons exhibiting highly efficient spontaneous emissions.
Fabrication and Characterization of Novel Oxide-Free InP Metal-Insulator-Semiconductor FETs Having an Ultra Narrow Si Surface Quantum Well
Authors: Yamada Masatsugu , Takahashi Hiroshi , Hashizume Tamotsu , Hasegawa Hideki
Published: October 2002

A novel oxide-free InP metal-insulator-semiconductor field-effect transistor
(MISFET) with an ultra narrow Si surface quantum well in the gate structure was
proposed and fabricated. The ultra thin Si3N4/Si interface structure was
realized by molecular-beam epitaxy (MBE) growth and partial nitridation of a
pseudomorphic Si interface control layer (Si ICL) on an InP epitaxial layer. Passivation
effect of the InP surface was monitored in situ by X-ray photoelectron
spectroscopy (XPS) and ultrahigh vacuum (UHV) contactless capacitance–voltage
(C–V) methods. A strong surface passivation effect was achieved after partial
nitridation of the Si ICL with an optimal nitridation time. The fabricated MISFET with
the Si-ICL passivation exhibited excellent gate control capability and stable operation.
The drift of the drain current was found to be as small as 1.9% after 104 s
operation.
Germanium- and Zinc-Doped P-type InAsSb Single Crystals with a Cutoff Wavelength of 12.5 µm
Authors: Gao Yu Zhu , Kan Hirofumi , Aoyama Mitsuru , Yamaguchi Tomuo
Published: October 2002

We grew germanium (Ge)- and zinc (Zn)-doped p-type InAs0.04Sb0.96 epilayers with a cutoff wavelength of 12.5 µm on n-InAs substrates by melt epitaxy (ME), and undertook a study of the properties of Ge-doped long-wavelength p-InAsSb epilayers. The quality of the epilayers was evaluated by transmittance, electroprobe microanalysis (EPMA) and Van der Pauw measurements. The results showed that the cutoff wavelength of the InAsSb epilayers with different levels of Ge doping showed no significant changes when the composition of the epilayers was kept constant. The Ge distribution, both on the surface and along the growth direction of the epilayer, is rather homogeneous. A maximum hole mobility of 1120 cm2/Vs with a carrier density of +9.18 ×1016 cm-3 at 77 K was achieved in a Ge-doped p-InAsSb epilayer. However, in the case of a Zn-doped epilayer, a hole mobility of 860 cm2/Vs with a carrier density of +2.48 ×1017 cm-3 was obtained at 77 K.
Thermal Stability of a RuO2 Electrode Prepared by DC Reactive Sputtering
Authors: Matsui Yuichi , Hiratani Masahiko , Kimura Shinichiro
Published: October 2002

RuO2 films were deposited by reactive DC sputtering, and the formation process
and the thermal stability were investigated. In the RuO2/Ti/SiO2 structure, the Ti
surface was preferentially oxidized at the initial stage of RuO2 growth. Insertion of Ru
and TiN layers between the RuO2 and Ti layers can suppress the oxygen diffusion
toward the Ti layer during the film growth. However, when the RuO2/Ru/TiN/Ti/Si
structure was heat-treated, the RuO2 was partially reduced to form RuO2-X
and the TiN
was oxidized to TiO2 while generating N2 and O2 gases, resulting in voids formation at
the RuO2/Ru interface, regardless of the heat-treatment atmosphere. We found this was
caused by internal oxygen diffusion within the stacked layers. This reaction is governed
by the transference of oxygen to the TiN and Ti layers by the difference in the Gibbs'
formation free energy, and by the oxygen diffusion enhancement.
Stabilization of PN Heterojunction between Cu(InGa)Se2 Thin-Film Absorber and ZnO Window with Zn(O, S, OH)x Buffer
Authors: Kushiya Katsumi , Yamase Osamu
Published: October 2002

Dramatic improvement of current–voltage (I–V) performance, especially
the fill factor (FF) observed in the Cu(InGa)Se2-based thin-film circuits with
Zn(O, S, OH)
x
buffer after postdeposition light soaking is discussed in this
study. Considering the composition of Zn(O, S, OH)
x
buffer and the reversible
behavior with respect to postdeposition light soaking, a model is proposed, in which
H2O molecules released by the dehydration of Zn(OH)2 in the
Zn(O, S, OH)
x
buffer are considered to play a dominant role in this behavior.
Based upon this model, attempts to stabilize the pn heterojunction by making the
reversible behavior irreversible are, for the first time, successfully achieved by
adjusting the postdeposition light-soaking conditions. The reduction of the
Zn(OH)2 concentration in the Zn(O, S, OH)
x
buffer through the combination
of heating at 130°C for at least 40 min and irradiation using a constant-light
solar simulator contributes to stabilizing the pn heterojunction and improving the
I–V performance as well as the electrical yield.
The Influence of Adjacent Preformat Pits on Magneto-Optical Signals
Authors: Umezawa Tomokazu , Horiguchi Toru , Tomie Takashi , Nakatani Kenji
Published: October 2002

Fluctuations in magneto-optical (MO) signals have been observed in
3.5-in. 640 MB MO disks which have the zone constant angular velocity (ZCAV) format.
They were found to occur at the border of each band (zone) when there were preformat
pits in the adjacent band. The fluctuations were observed in those MO disks whose
substrates were injection molded polycarbonate (PC). The degree of these MO signal
fluctuations depended on the injection molding conditions of the substrates and the
phase shift of the optical head. It is thought that such phenomena can be attributed to
tilted ellipsoids of substrate birefringence that occur around preformat pits, and which
are caused by stresses induced around the preformat pits during the injection molding
process.
The Study of Interface States in ZnO Varistors by Injection Pulse Width Dependence of Transient Response
Authors: Yasuhiro Ohbuchi Yasuhiro Ohbuchi , Toshio Kawahara Toshio Kawahara , Yoichi Okamoto Yoichi Okamoto , Jun Morimoto Jun Morimoto
Published: October 2002

The injection pulse width dependence of transient response was studied to investigate the interface states in the Bi- and Pr-type ZnO varistors in more detail using isothermal capacitance transient spectroscopy (ICTS). Although the interface states have been considered to be distributed monoenergetically or discretely, two or three different interface states of the emission process were confirmed by varying the injection pulse width at each measurement temperature. For both types of ZnO varistors, the ICTS spectrum overlapping of the interface states consists of two transient responses: the previously reported trap (Trap 1) and Trap 0 which has a faster emission process than Trap 1. For only Bi-type ZnO, Trap 2 which has a slower emission process, was successfully detected at the longer region of the injection pulse widths t
W from 1 s to 100 s. This result suggests that the formation of Trap 2 can be attributed to the existence of Bi2O3. In the case of the application of ICTS for the interface states in ZnO varistors, it is necessary to select the optimal injection pulse width which takes into account the emission processes at each measurement temperature.
Configuration Optimization of a Reflective Bistable-Twisted-Nematic Cell for High-Contrast Operation
Authors: Lee Gi-Dong , Kim Gi-Hong , Yoon Tae-Hoon , Kim Jae Chang
Published: October 2002

In this study, the configuration of a reflective
bistable-twisted-nematic (BTN) liquid-crystal cell is optimized for
high contrast and high brightness operation. We searched for the
optimum optical parameters of a reflective BTN cell by calculating
its optical performances at three wavelengths; red, green, and
blue. By studying the effect of each optical parameter on the
optical performances, we found that the angle of the polarizer is
more important than any other optical parameter in the design of a
reflective BTN cell. We fabricated a reflective BTN cell with a
wide-band retardation film, whose measured contrast ratio is 10.6:1.
Surface Treatment by Ar Plasma Irradiation in Electron Cyclotron Resonance Chemical Vapor Deposition
Authors: Hashimoto Jun-ichi , Ikoma Nobuyuki , Murata Michio , Fukui Jiro , Nomaguchi Toshio , Katsuyama Tsukuru
Published: October 2002

To reduce the surface states of GaAs and related semiconductors which originate
from native oxides on a surface, we developed a simple surface treatment method in
which the surface oxides could be physically sputtered by Ar plasma irradiation in an
electron cyclotron resonance chemical vapor deposition (ECR-CVD) apparatus. In the
experiment of Ar irradiation of a GaAs surface, we were able to determine the optimum
irradiation time at which the native-oxide-related surface states were almost removed
without damaging the irradiated surface. Then, we applied this method to an actual
0.98-µm semiconductor laser in which catastrophic optical damage (COD) failure
occurred due to the surface states of the output facet. By irradiating Ar plasma to the
output facet of the laser and removing the oxide-related surface states there, tolerance
to COD was remarkably improved compared with that of a conventional
non-Ar-irradiated one.
Cantilever Type Lead Zirconate Titanate Microactuator Utilizing Ruthenium Oxide
Authors: Lee Sun-Ho , Jeon Min-Seok , Hong Kyung-Il , Lee Jin-Won , Kim Chang-Kyung , Choi Duck-Kyun
Published: October 2002

A new and simple cantilever type Pb(Zr, Ti)O3 [PZT]
microactuator was fabricated by adopting RuO2. The RuO2
has reasonably good conductivity and stiffness and it can replace
the double layer of electrode and supporting layer to a single layer
in a cantilever beam. The RuO2, PZT and Al thin films were
deposited on the Si substrate. The patterning of the Al was carried
out by a lithography process and etched with a chemical wet
etchant. The etching of PZT and RuO2 were performed by a
reactive ion etching system. The Si was etched isotropically to form
a cantilever beam. The fabricated cantilever beam consists of Al,
PZT and RuO2, and the thicknesses of the films are 0.40, 0.25
and 0.70 µm, respectively. The beams were from 140 µm to
275 µm in length and all of them were 60 µm wide. Driving
tilt angles of the cantilever beams were almost proportional to the
applied voltages.
Asymmetrical Property of 1/f Resistance Fluctuation for Time Inversion
Authors: Akabane Hideo , Nakaya Kazuyoshi , Agu Masahiro
Published: October 2002

The 1/f resistance fluctuations of carbon fiber are observed under four
different nonequilibrium conditions controlled by the heat diffusion from the fiber to
the external environment. A higher-order correlation function of an observed 1/f time
series is analyzed and compared with those of three different types of
computer-generated 1/f time series. It is found that the higher-order correlation
function related to the time-inversion asymmetry of the 1/f resistance fluctuation
shows the same statistical property as that of a one-dimensional diffusion system.
Further more, the higher-order correlation function of the 1/f resistance
fluctuations with the same 1/f spectra is shown to be affected by the heat diffusion
from the carbon fiber.
Experimental Study of Cloud Formation by Intense Electric Fields
Authors: Teramoto Kazuhiko , Ikeya Motoji
Published: October 2002

Cloud and fog formation under an electric field has been studied experimentally
using a Wilson's cloud chamber with a supercooled atmosphere of ethanol. The threshold
electric field to generate dense clouds using parallel plate electrodes was about
4 kV/m as estimated from the generated cloud position and from a model experiment
of an electric field simulation using a water bath. Positive ions produced by the
ionization of the atmosphere condense nuclei for the generation of fogs and clouds. Old
legends and retrospective reports on earthquake fogs (EQFs) and clouds (EQCs) prior to
a major shock may be elucidated by the condensation of vapor under an intense electric
field, similar to earthquake lightning (EQL) due to electro-atmospheric arc and dark
discharges. A plume cloud like a streamer discharge was produced from a needle
electrode, which exhibited similarities to tornado-type clouds photographed before the
Kobe earthquake. Electric discharges of clouds by a wired rocket or laser-induced
lightning are suggested to terminate the electric energy for the upward vortex flow of
a tornado.
Physical Principles and Theoretical Concepts of Transient Acoustic Field
Authors: Otani Takahiko
Published: October 2002

Short impulsive acoustic waves are widely applied today to
acoustical imaging systems for medical diagnosis, nondestructive
testing and underwater geophysical survey to obtain a better range
resolution. The waveform of short impulsive waves are considerably
deformed according to the distance from the acoustic source and the
axial angle, and consequently the range resolution and the azimuth
resolution are incompatible. The transient acoustic field radiated
by a piston source and the phenomenon of waveform deformation of the
transient acoustic field are discussed. It is shown that the
directional characteristics of a transient wave depend on the
acceleration waveform as well as on the configuration and dimensions
of the radiator surfaces and that the directivity pattern is
essentially dependent on the reciprocal of sin
θ.
Coefficients of Coupled-Mode Equations for a Natural-Single-Phase-Unidirectional Transducer and an Electrode-Width-Difference-Reversal-of-Directivity Transducer on a 50° Y-24° X La3Ga5SiO14 Substrate
Authors: Koji Hasegawa Koji Hasegawa , Kiyoshi Inagawa Kiyoshi Inagawa , Masanori Koshiba Masanori Koshiba
Published: October 2002

Computed results of all the coefficients of coupled-mode equations
are presented for a natural-single-phase-unidirectional transducer (NSPUDT)
and an electrode-width-difference-reversal-of-directivity transducer
on a 50° Y-24° X
La3Ga5SiO14 substrate.
In order to determine all the coefficients,
edge frequencies of a stop-band, standing-wave distributions
at these frequencies on a substrate surface,
and static capacitances of a transducer are calculated
using the hybrid finite-element method.
Therefore,
all the effects of piezoelectric perturbation,
mechanical perturbation, and energy storage due to nonradiated bulk
waves are taken into account.
The aluminum electrode width dependences of the coefficients are investigated in
detail.
Numerical results reveal that
we can choose pairs of width and height of the active electrodes
for a distance of λ/8 with λ being
the surface acoustic wave wavelength at the center frequency between the reflection
center and the transduction center.
Our results of the transducer loss for NSPUDT agree well with previous
experimental ones.
Wavelength-Division-Multiplexed Photonic Switching System Using Integrated Acoustooptic Switches
Authors: Nobuo Goto Nobuo Goto , Yasumitsu Miyazaki Yasumitsu Miyazaki
Published: October 2002

Collinear acoustooptic (AO) wavelength separators and switches consisting of an optical directional coupler have been investigated near the wavelength of 0.6 µm. The fundamental characteristics of wavelength-selective switching are investigated at the fiber communication wavelength of around 1.55 µm for use in wavelength-division-multiplexed (WDM) networks and photonic switching systems, in comparison with those in the visible wavelength range. As applications to WDM optical systems, optical add/drop multiplexers (ADMs) for WDM network-accessing systems, matrix switches for WDM crossconnects and photonic switching systems are discussed.
Ultrasonic Measurement of Sound Velocity in Liquids by a Phase-Locked Loop
Authors: Kiyoshi Ikeda Kiyoshi Ikeda
Published: October 2002

This paper describes a new ultrasonic technique for measuring the velocity of sound in liquids which relies on a phase-locked loop method to automatically eliminate dependence of the result on temperature. An empirical equation using NaCl solutions as test liquids within a concentraion range of 0.0–5.0% and a temperature range of 15–45°C was obtained by analyzing the various sound velocities by the least squares method.
An empirical equation was derived to design a compensatory voltage-controlled oscillator (Comp VCO) which would automatically eliminate the strong temperature dependence of the measured sound velocity in liquids. The sound velocity after eliminating temperature dependence was easily obtained from the output frequency of the Comp VCO by multiplying the coefficient. A system with a Comp VCO circuit was applied to NaCl solutions of varying concentrations and was shown to yield velocities accurate to within 0.024% independent of temperature variations of ±1.3°C at approximately 24.9°C.
Detection of Ultrasonic Mechanical Vibration of a Solid Using Fiber Bragg Grating
Authors: Takahashi Nobuaki , Yoshimura Kazuto , Takahashi Sumio
Published: October 2002

Based on the intensity modulation of laser light propagating
through a fiber Bragg grating (FBG) attached to a Pb(Zr, Ti)O3
(PZT) vibrator, the detection of mechanical vibration is
demonstrated. The output of the sensor is stable and the involved
harmonic component is small. It is considered that the sensor
operation is linear. The sensitivity depends on the slope of the FBG
transmission spectrum curve at the operating wavelength and is
higher for a steeper slope. Since not only an FBG has little
influence on the object being measured because of its smallness and
light weight but also its frequency characteristics are thought to
be better than those of a PZT vibration sensor, an FBG is expected
to provide us with an important tool of practicality for measuring
mechanical vibration.
Grain Bulk Modulus of Marine Sediment
Authors: Kimura Masao
Published: October 2002

In this study, the value of the grain bulk modulus of marine sediment has been
investigated. Glass beads are used for the sand model. The value of the grain bulk
modulus for glass beads is obtained from the measured values of longitudinal and shear
wave velocities in glass beads. The value of the grain bulk modulus is also estimated
from the measured values of the longitudinal wave velocity in a heavy liquid suspension
of glass beads. From the above results, it is seen that the measured values of the grain
bulk modulus are nearly the same as Stoll's value of the grain modulus.
Moreover, it is suggested that the unjacketed bulk modulus may not be the same as the
grain bulk modulus.
A Method of Tissue Elasticity Estimation Based on Three-Dimensional Displacement Vector
Authors: Naotaka Nitta Naotaka Nitta , Tsuyoshi Shiina Tsuyoshi Shiina
Published: October 2002

For assessing the tissue elastic properties based on 3D information of displacement and strain induced by static deformation, we propose an estimator of 3D displacement vectors. This method is composed of the combination of the weighted phase gradient method (WPG), which utilizes the gradient of the plane obtained from the phase shift at each receiving element on the 2D array, and combined autocorrelation method (CA), which is phase domain processing without aliasing. Large displacements required for highly accurate measurements can be measured by this method. In addition, we develop a tissue elasticity reconstruction method using the measured 3D displacement vectors. Computer simulations reveal that our methods are valid for evaluating the elastic structures of tissues based on 3D information.
Suppression of Floating Body Effects by Controlling Potential Profile in the Lower Body Region of Silicon-on-Insulator Metal-Oxide-Semiconductor Field Effect Transistors
Authors: Sato Yasuhiro , Tsuchiya Toshiaki
Published: October 2002

This paper describes a promising way to suppress floating body
effects (FBE) in fully depleted (FD) silicon-on-insulator
metal-oxide-semiconductor field-effect transistors (SOI MOSFETs),
which is applicable to the complementary MOS (CMOS) structure. The
FBE is suppressed by controlling the potential profile by supplying
an adequate positive substrate voltage (V
SUB). FD SOI
NMOSFETs show a strong dependence of V
T on
V
D in the higher V
D range, which is
induced by the FBE. The accumulation in the body of holes generated
through impact ionization raises the body potential, and hence
lowers V
T. A positive V
SUB improves the
anomalous subthreshold slope, and thereby weakens the dependence of
V
T on V
D. This is
mainly because the positive V
SUB lowers the potential barrier height for holes in the lower body region, which enhances the flow of holes
in the body into the source, and thus suppresses the increase in
body potential. The decrease in the potential barrier height for
holes is supported by two-dimensional device simulation. Supplying a
positive V
SUB causes hardly any changes in the characteristics of SOI P-channel MOSFETs (PMOSFETs). Therefore, supplying a positive
voltage to the substrate is useful for the SOI CMOS structure.
Enhancement of Open Circuit Voltage via Light soaking in Amorphous Silicon Solar Cells
Authors: Isomura Masao , Kondo Michio , Matsuda Akihisa
Published: October 2002

The increase in open-circuit voltage (V
oc) due to
light soaking was investigated in amorphous silicon solar
cells. The light-induced increase in V
oc appears when
i-layers are prepared in H2-diluted plasma
(H2/SiH4>10). It is necessary that more than
two-thirds of the i-layer thickness be formed under such hydrogen
dilution. This phenomenon is not related to p/i interface effects
but reflects the bulk properties of the dilution layer. The increase
in V
oc is caused by the voltage shift of dark I–V
characteristics. The change of V
oc is determined by the
balance between the shift of dark current and the reduction of
photocurrent due to the light-induced defects. The voltage shift
suggests an increase in the diode barrier height of the pin
junction; however, the increase in built-in potential in the active
layers (i-layers) is not observed in our experiments. The advantage
of this effect is seen with sufficiently thin i-layers, because
conventional light-induced degradation is negligible. The increase
in V
oc improves conversion efficiency by 2% after light
soaking in the case of 500 Å i-layers.