bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous Kinetics of the Volume Phase Transition in Poly-N-Isopropylacrylamide Gels
Authors: Hirotsu Shunsuke
Published: October 2002

Extreme speeding-up of a large, discontinuous volume change at the volume phase transition of poly-N-isopropylacrylamide (PNIPA) gels has been realized. The gels prepared by the new method undergoes a shrinking transition faster by six orders of magnitude as compared with conventional PNIPA gels. The relaxation time of the volume shrinkage can be controlled from seconds to months on the same size of gels. A plausible mechanism of the dramatic speeding-up of the volume phase transition, as well as the mechanism of extremely slow kinetics of the conventional PNIPA gels are proposed.
Evolution of Surface Morphology and Strain in Low-Temperature AlN Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Shim Kyu-Hwan , Myoung Jaemin , Gluschenkov Oleg , Kim Kyekyoon , Kim Chinkyo , Robinson Ian K.
Published: October 2002

The evolution of stress-driven surface roughening in low-temperature (LT) grown AlN has been investigated in a wide range of film thicknesses using plasma assisted molecular beam epitaxy and atomic force microscopy analysis. The relaxation of residual strain causing morphological instability after ∼50 nm thickness represents the kinetic stabilization of LT growth. LT-AlN layers with thicknesses of ∼20 nm provide excellent surface smoothness of <0.9 nm and large relaxation, ∼94% of the lattice mismatch strain. AlN films thicker than 50 nm, for which the scaling exponents are greater than 1, revealed stress-driven surface roughening with coherent islands. The implementation of thick LT-AlN buffer layers is limited by the stress-driven surface roughening above ∼50 nm thickness.
Size-Dependent Enhancement of Third-order Optical Nonlinearity in CuBr xCl1- x Nanocrystals Embedded in Glass
Authors: Li Yingli , Ohata Manabu , Satoshi Sasaki and Arao Nakamura Satoshi Sasaki and Arao Nakamura
Published: October 2002

We have studied the size-dependence of the third-order optical nonlinearity in CuBrxCl1-x
(x=0.26±0.01) nanocrystals with radii ranging from 5.3-11.5 nm by means of degenerate four-wave mixing, time resolved luminescence and resonant luminescence experiments. The absolute value of third-order susceptibility χ(3) exhibits resonant behavior at the confined exciton level, and the resonant χ(3) increases with increasing crystallite radius R. Assuming a two-level atomic model, we have analyzed the size-dependence of χ(3) and obtained the R
2.1-dependence of the oscillator strength of confined excitons. The figure of merit increases from 0.65 to 3.4 esu·cm/s with increasing size.
Effects of Substrate Misorientation on the Formation and Characteristics of Self-Assembled InP/InGaP Quantum Dots
Authors: Guk Jeong Yong-Hwan Kwon
Published: October 2002

The structural and optical characteristics of self-assembled InP/InGaP quantum dots grown by low-pressure metalorganic vapor phase epitaxy on GaAs substrates misoriented by 0°, 2°, 5°, 6°, and 35.3° toward (111)A are investigated. The analysis through atomic force microscopy and photoluminescence (PL) shows that the formation of quantum dots strongly depends on the orientation of the substrate. It is seen that large dots are more easily formed on an exactly (001) substrate but, with the increase of the degree of misorientation, the size of dots decreases and the density increases. In addition, the PL emission energy from InP dots is observed to be strongly blue-shifted with the increase in misorientation. From power-dependent PL measurement, the change of PL spectra is observed to be closely related to the size and density of the quantum dots.
Highly Efficient Persistent Hole-Burning in Cuprous Halide Quantum Dots
Authors: Tadashi Kawazoe Tadashi Kawazoe , Yasuaki Masumoto Yasuaki Masumoto
Published: October 2002

Formation efficiencies of the persistent holes in various kinds of cuprous halides quantum dots, namely CuCl, CuBr and CuI quantum dots, embedded in glass or alkali halide crystals, were measured. The highest quantum efficiency of 0.097 was obtained at 2 K for CuCl quantum dots in glass. The persistent absorption decrease of quantum dots caused by a photon is larger than that of the most efficient ionic or molecular persistent hole-burning materials by 3 orders of magnitudes. The high sensitivity shows that the persistent hole-burning phenomenon in semiconductor quantum dots has potential for application in the multiple optical memory devices.
In Situ Monitoring of Silicon Surfaces During Reactive Ion Etching
Authors: Sakikawa Nobuki , Shishida Yoshinori , Miyazaki Seiichi , Hirose Masataka
Published: October 2002

Surface chemical reactions during reactive ion etching (RIE) of silicon in a CF4+O2 plasma have been investigated by employing in situ Fourier-transform infrared attenuated total reflection (FT-IR ATR) spectroscopy. It is shown that a surface reaction layer with a thickness of 2–4 nm is composed of SiF
X
(X=1, 2, 4 and presumably 3) and SiO
Y
(Y< 2) bonds. The SiF
X
bond concentrations in the surface reaction layer are almost independent of O2 gas concentration in the plasma because they are located mainly at the subsurface layer/Si interface. The etch rate is determined by the oxidized subsurface layer thickness and fluorine radical flux penetrating into the interface region, where the etch products SiF
X
are formed.
Low-Voltage Optical Fiber Switch
Authors: Tseng Shiao-Min , Chen Chin-Lin
Published: October 2002

In conjunction with nematic liquid crystal, an optical fiber switch directly fabricated on a single-mode side-polished fiber was successfully demonstrated. The principle of operation, fabrication and performances of the switch are presented. An operating voltage as low as 30V
p-p was demonstrated.
The Superiority of N 2O Plasma Annealing over O 2 Plasma Annealing for Amorphous Tantalum Pentoxide (Ta 2O 5) Films
Authors: Lau Wai Shing , Perera Merinnage Tamara Chandima , Babu Premila , Ow Aik Keong , Han Taejoon , Sandler Nathan P. , Tung Chih Hang , Sheng Tan Tsu , Chu Paul K.
Published: October 2002

As-deposited tantalum pentoxide (Ta2O5) films are amorphous. The films will remain amorphous after low-temperature O2 or N2O plasma annealing. High-temperature annealing will produce polycrystalline films where grain boundaries can generate leakage current. It was found that N2O plasma annealing is superior to O2 plasma annealing in terms of leakage current reduction. This can be easily explained by the lower energy required to break the nitrogen-oxygen bond in a N2O molecule compared to the energy required to break the O=O bond in an O2 molecule. We also observed that there is less Si contamination, which may lead to leakage current, in the sample with N2O plasma annealing compared to the sample with O2 plasma annealing.
Superstrate-Type Cu(In, Ga)Se2 Thin Film Solar Cells with ZnO Buffer Layers
Authors: Nakada Tokio , Kume Tomoyuki , Mise Takahiro , Kunioka Akio
Published: October 2002

We have proposed the use of ZnO as a new buffer material in superstrate-type
Cu(In, Ga)Se2 (CIGS) solar cells. Little or no interdiffusion was found at the ZnO/CIGS interface,
allowing the use of high temperatures for CIGS deposition. As a result, superstrate-type CIGS solar
cells with efficiencies reaching as high as 10% were achieved for the first time by using this buffer
material along with the inclusion of sodium sulfide (Na2S) during CIGS deposition.
Optical Recording in Ga and In-Doped Zinc Oxide Thin Films Grown by Radio-Frequency Magnetron Sputtering
Authors: Tatsuhiko Matsushita Tatsuhiko Matsushita , Akio Suzuki Akio Suzuki , Shogo Toda Shogo Toda , Takanori Aoki Takanori Aoki , Masahiro Okuda Masahiro Okuda
Published: October 2002

Thin films of Zn-Ga-In oxide have been deposited on glass substrate at room temperature by rf magnetron sputtering with three targets of Zn, ZnO doped with 7 wt% Ga2O3 and ZnO doped with 7 wt% In2O3. In the oxide films prepared by this method, the difference in the transmittance, ΔT, between the annealed state(350°C × 30 min) and the as-deposited state was 41% at 380 nm, 61% at 390 nm and 72% at 400 nm. The ability to record on these oxide films without a protection layer, using SHG of Nd:YAG laser (λ=532 nm, 6 ns, 69 mW/µm2) was confirmed.
Atomic Beam Alignment of Liquid Crystals
Authors: Chaudhari Praveen , Lacey James A. , Lien Shui-Chih Alan , Speidell James L.
Published: October 2002

We have found that liquid crystals can be aligned on a polyimide surface exposed to a low energy and neutral argon ion beam. The energy of the incident ions was varied between 75 eV and 500 eV, the integrated current density from 20 µA/cm2 to 500 µA/cm2, and the angle of incidence over which alignment was measured was between 10° and 80°. The pretilt angle of the liquid crystals could be varied between 0° and 10°, by controlling the processing conditions.
Sponge of Purified Carbon Nanotubes
Authors: Ando Yoshinori , Zhao Xinluo , Ohkohchi Masato
Published: October 2002

We first used an infrared radiation heating system in air to purify multiwalled carbon nanotubes (MWNTs) containing unnecessary carbon nanoparticles. The raw MWNTs were obtained in the cathode deposit when a graphite electrode was evaporated in hydrogen gas by DC arc discharge. The purification reached the depth of 0.1 mm from the deposit surface, which revealed highly oriented MWNTs vertical to the cathode surface. Using this methode, we can easily obtain a spongy bulk of highly oriented and purified MWNTs, with the size on the order of 10 mm2 in surface area and 0.1 mm in thickness.
Single Crystal Growth of the Icosahedral Zn-Mg-Ho Quasicrystal
Authors: Taku J. Sato Taku J. Sato , Hiroyuki Takakura Hiroyuki Takakura , An Pang Tsai An Pang Tsai
Published: October 2002

Single crystal growth of the icosahedral Zn-Mg-Ho quasicrystal has been performed using the Bridgeman method.
Composition of the starting alloy was selected as Zn46Mg51Ho3, so that the icosahedral phase directly precipitates from the liquidus phase.
A large single quasicrystal about 0.5 cm3 in size was obtained, and its composition was determined as Zn60Mg31Ho9.
The obtained quasicrystal shows an extremely high structural-perfection evidenced by the X-ray Laue reflection and neutron diffraction methods.
Theoretical Analysis of Write Errors and Number of Stored Electrons for Ten-Nanoscale Si Floating-Dot Memory
Authors: Tatsuya Usuki Tatsuya Usuki , Toshiro Futatsugi Toshiro Futatsugi , Anri Nakajima Anri Nakajima
Published: October 2002

A basic trade-off between write errors, the number of stored electrons and applied voltage
was obtained for ten-nanoscale Si floating-dot memory, which was studied as a
single electron device. For the ten-nanoscale dot size, more than seven electrons are necessary
for reliable writing at room temperature. Furthermore, to retain writing accuracy, we have to increase the applied voltage if the floating-dot size is reduced to single electron operation.
Such ten-nanoscale memory with a small number of electrons can still have a small
energy consumption of about 5×10-19 J per writing operation. This will be the new target instead of using single electron devices.
Attosecond Pulse Generation Using High Harmonics of the KrF Laser Driver Pulse
Authors: Kien Fam Le , Katsumi Midorikawa Katsumi Midorikawa , Akira Suda Akira Suda
Published: October 2002

High-harmonic generation from He atoms illuminated by high-intensity femtosecond KrF laser pulses is studied.
It is shown that single attosecond pulses as well as trains of several attosecond pulses, one per half-a-period, can be generated in the several-cycle regime of the intense driver pulse.
Deposition of Hydrogenated Amorphous Silicon under Intermittent Substrate Bias
Authors: Sakikawa Nobuki , Shishida Yoshinori , Miyazaki Seiichi , Hirose Masataka
Published: October 2002

Hydrogenated amorphous silicon (a-Si:H) was deposited using a triode-type reactor to which
an intermittent substrate bias was applied. The total bonded hydrogen content was
reduced to 2.9 at.% at a substrate temperature of 200°C, and a photosensitivity of 5×106 with a dark
conductivity of 7×10-11 S/cm was obtained. The defect density measured using a constant
photocurrent method was as low as 8.5×1015 cm-3. It is suggested that the ion flux intermittently
impinging onto the growing film surface causes ion-induced hydrogen desorption and a-Si:H
network relaxation.
Electrical Resistivity of Eu-Rich EuO Thin Films
Authors: Konno Toyohiko J. , Wakoh Kimio , Sumiyama Kenji , Suzuki Kenji
Published: October 2002

The electrical resistivity of Eu-rich EuO thin films was studied at temperatures 5≤T≤150 K and magnetic fields 0≤H≤5 T. We prepared two films with different
degrees of off-stoichiometry using the method described previously. [Jpn. J. Appl. Phys. 35 (1996) 6052] The film richer in Eu exhibited an increase in
Curie temperature of the bulk value of 70 K to approximately 150 K, and zero-field resistivity decreased from about 100 µ Ω·m at 100 K to 5 µ Ω·m at 20 K. The film's magnetoresistance exceeded -80% in the 80–90 K temperature range.
These results show that the stable reproduction of EuO films with high levels of conductivity without the addition of a third element is now possible.
Uniform RF Discharge Plasmas Produced by a Square Hollow Cathode with Tapered Shape
Authors: Taichi Fukuda Taichi Fukuda , Akio Matsuoka Akio Matsuoka , Yoshiomi Kondoh Yoshiomi Kondoh , Minoru Sugawara Minoru Sugawara
Published: October 2002

A square hollow cathode with a tapered shape (square HCT) is developed in order to produce highly uniform and dense plasmas (density ∼ 6×1010 cm-3) with a wide range of operating pressures. It is shown experimentally that the plasma density produced by the HCT is higher than that produced by a plane cathode from 0.02 Torr to 0.2 Torr. It is demonstrated experimentally that uniform plasmas can be produced by modifying the structure of the HCT for different operating pressures. It is shown that an additional outer hollow cathode is useful to compensate the nonuniformity of plasmas due to edge effects. With the use of the outer hollow cathode for the modified HCT, highly uniform plasmas are produced within almost the entire surface of the grounded square electrode.
Origin of the F-aggregate Centers in BaFX(X=Cl, Br) Single Crystals
Authors: Toshio Kurobori Toshio Kurobori , Shuichi Kozake Shuichi Kozake , Yukio Hirose Yukio Hirose , Karnati Somaiah Karnati Somaiah , Katsuyuki Inabe Katsuyuki Inabe , Masato Ohmi Masato Ohmi , Masamitsu Haruna Masamitsu Haruna
Published: October 2002

Some new experimental evidence to determine the origin of the F-aggregate centers located in the near IR region in BaFX(X=Cl, Br) crystals is demonstrated. The attribution of the F-aggregate bands to a cluster of the F(X-) centers has been confirmed through a series of measurements on their emission in IR and the process of aggregates formation in BaFCl1-x
Br
x
mixed system. The F-aggregate bands at 860 and 1100 nm are assigned to the F(X-)2 and F(X-)4 centers, respectively, in view of the equilibrium between the F(X-) centers and the F-aggregate centers.
Aggregation of Dendrimers with a Photochromic Dithienylethene Core Group on the Mica Surface-Atomic Force Microscopic Imaging
Authors: Hellmann Jörg , Hamano Mitsuo , Karthaus Olaf , Ijiro Kuniharu , Shimomura Masatsugu , Irie Masahiro
Published: October 2002

Atomic force microscopic (AFM) imaging revealed that a polyether third
generation dendrimer having a photochromic dithienylethene core group forms
regularly aligned (hexagonal alignment) droplets of more or less equal size (100–120 nm) and height of the long axis of the dendrimer (5.0±0.5 nm) on a mica
surface when the surface is rinsed with a benzene solution of the dendrimer. The
size suggests that one droplet contains around 104 dendrimers. The subtle
balance among surface hydrophilicity, hydrophobicity of solvent and dendrimers,
and structure or shape of the dendrimers is considered to control the regular
alignment.
Investigation of High-Efficiency InGaP/GaAs Tandem Solar Cells under Concentration Operation
Authors: Yang Mingju , Takamoto Tatsuya , Ikeda Eiji , Kurita Hiroshi , Yamaguchi Masafumi
Published: October 2002

The photovoltaic properties of InGaP/GaAs tandem solar cells under
concentration have been investigated for concentration application. A high
efficiency of 31.2% has been obtained for the InGaP/GaAs tandem solar cell
under 5.1 suns of AM1.5 illumination. However, as the light intensity further
increases, the efficiency is limited due to the reduction in the fill factor. The
results show that not only very high peak current density, J
p, of the tunnel
diode but also the valley current density, J
v, of the tunnel diode is necessary for
high concentration. The efficiency predictions of the InGaP/GaAs tandem cell
based on a numerical analysis suggest that a conversion efficiency of over 35%
will be obtained at 500 suns if the series resistance of less than 0.001 Ω/cm2 is
realized. Photocurrent mismatch between the top and bottom cells during
high-temperature operation has also been analyzed for the design of
concentrator cells.
Imaging of Local Charge Density in an InAs/GaAs Two-Dimensional Heterostructure by Scanning Tunneling Microscopy
Authors: Hiroshi Yamaguchi Hiroshi Yamaguchi , Yoshiro Hirayama Yoshiro Hirayama
Published: October 2002

We have studied the bias-voltage dependence of
constant-current images obtained by
scanning tunneling microscopy (STM) at 4.8 K
on an InAs thin film grown on GaAs (111)A substrates.
In-plane surface-height variation as large as 0.1–0.2 nm was detected
on the step-free region,
only with the negative sample voltages higher than -0.6 V.
Because the bias condition corresponds to the tunneling
of electrons accumulated in the InAs film to the STM tip,
we believe that the image reflects the local electron density
in InAs/GaAs two-dimensional heterostructures.
Characterization and Control of Domain Structure in SrBi2Ta2O9Thin Films by Scanning Force Microscopy
Authors: Gruverman Alexei , Ikeda Yuji
Published: October 2002

We used the piezoresponse mode of scanning force microscopy (SFM) to perform the first nanoscale observation of ferroelectric domain structure in as-grown SrBi2Ta2O9films. By lowering the loading force down to approximately 1 nN and by keeping the imaging voltage just below the coercive voltage, we managed to obtain a sufficiently high contrast between opposite 180° domains without affecting the original domain structure. Local and large-scale ferroelectric switching with subsequent readout in areas of about 0.01 µm2and 1.5 µm2, respectively, were carried out by applying pulsed- and dc-voltage bias through the conductive tip.
Selective Area Growth of GaN on Si Substrate Using SiO 2 Mask by Metalorganic Vapor Phase Epitaxy
Authors: Yasutoshi Kawaguchi Yasutoshi Kawaguchi , Yoshio Honda Yoshio Honda , Hidetada Matsushima Hidetada Matsushima , Masahito Yamaguchi Masahito Yamaguchi , Kazumasa Hiramatsu Kazumasa Hiramatsu , Nobuhiko Sawaki Nobuhiko Sawaki
Published: October 2002

Selective area growth (SAG) of GaN on (111) Si substrate was studied using AlGaN as an intermediate layer. A hexagonal dot with a (0001) plane on the top and of a 5 µm or a submicron size was obtained using a patterned dot structure of silicon dioxide (SiO2) mask. The facet structure revealed that the <1120> axis of hexagonal GaN is parallel to the <110> axis of the Si substrate. The cathodoluminescence (CL) spectrum at 133 K exhibited a strong near-band-edge emission band for the submicron dots, which suggests excellent crystallinity. Epitaxial lateral overgrowth (ELO) of GaN on the Si substrate is demonstrated.
Energy Shifts of Auger Transitions of Ga, As and N during Plasma-assisted Nitridation of GaAs (001) Surface
Authors: Aksenov Igor , Nakada Yoshinobu , Okumura Hajime
Published: October 2002

Auger electron spectroscopy (AES) is used to study the processes taking place during the
initial stages of nitridation of GaAs(001)-2×4 surface by active nitrogen species generated by
a radio-frequency (RF) plasma source. Two effects, i.e. a chemical shift and a shift of the
Fermi level due to band bending, take place during nitridation, these effects causing shifts of
the Auger transitions of Ga, As and N. The shifts are the most pronounced for nitridation
temperatures in the range 300°C–400°C, when a uniform GaN layer is believed to be
formed on the surface. The post-nitridation thermal annealing of the samples nitrided in the
above temperature range leads to re-crystallization of the GaAsN phase, formed as a result of
nitridation, into cubic GaN layer.
Morphotropic Phase Boundary in Solid Solution Systems of Perovskite-Type Oxide Ferroelectrics
Authors: Ishibashi Yoshihiro , Iwata Makoto
Published: October 2002

The origin of the appearance of the morphotropic phase boundary in the
perovskite-type oxide solid solution systems and the increase in the dielectric
susceptibilities in the vicinity of the boundary is theoretically clarified on the basis
of a Landau-type free energy function. The dielectric susceptibilities are
concretely expressed in terms of the model parameters, and found to diverge at the
morphotropic phase boundary within the present model.
Effects of NH 3 Plasma Treatment of the Substrate on Metal Organic Chemical Vapor Deposition of Copper Films
Authors: Suk Kim Young , Joon Kim Donggeun Jung , Suk-Ki Min Suk-Ki Min
Published: October 2002

Surface modification by NH3 plasma treatment enabled selective copper (Cu) chemical vapor deposition (CVD) and
changed the structure of the deposited Cu film. After NH3 plasma treatment of the substrate, Cu nucleation was suppressed
on borophosphosilicate glass (BPSG), while Cu films were formed on TiN. NH3 plasma treatment was not as effective
as N2 plasma treatment in inducing the selectivity. The lower efficiency of the NH3 plasma in inducing the selectivity
can be explained by the generation of NH++ or H species. A Cu film deposited on plasma-treated TiN showed larger grains
and enhanced (111) preferential orientation compared with that deposited on untreated TiN, which could be explained in terms
of surface energy minimization.
Extra-Side-Facet Control in Selective Molecular Beam Epitaxial Growth of InGaAs Ridge Quantum Wires for Improvement of Wire Uniformity
Authors: Fujikura Hajime , Kihara Michio , HidekiHasegawa HidekiHasegawa
Published: October 2002

For InP-based InGaAs ridge quantum wires fabricated by selective
molecular beam epitaxy (MBE) on <110>-oriented InP mesa-stripes, the origin of wire inhomogeneity and the possible methods to improve the wire uniformity were investigated in detail. The appearance of extra-side-facets on (111)A sidewalls was found to be the major reason for ridge waving, leading to wire inhomogeneity. Use of mis-oriented mesa-stripes and high-temperature growth of InGaAs buffer layer were found to be significantly effective for reducing the width of the extra-facets, resulting in the suppression of ridge waving and a marked improvement of wire uniformity. The narrow photoluminescence (PL) peak of the InGaAs ridge quantum wire formed with the present extra-side-facet control indicated the realization of a wire having the best uniformity of all the InP-based InGaAs quantum wires reported so far and comparable or better uniformity than most of the GaAs-based quantum wires reported so far.
The Strong Correlation between Interface Microstructure and Barrier Height in Pt/n-InP Schottky Contacts Formed by an In Situ Electrochemical Process
Authors: Sato Taketomo , Kaneshiro Chinami , Hasegawa Hideki
Published: October 2002

In order to investigate the correlation between the microstructure of a metal/semiconductor (M/S) interface and the Schottky barrier height (SBH), Pt Schottky contacts were formed on n-type InP by an in situ electrochemical process under various electrochemical conditions; they were then investigated using scanning electron microscopy (SEM), current-voltage (I-V) and capacitance-voltage (C-V) measurements. Electrodeposition resulted in the formation of arrays of nanometer-sized Pt particles whose distribution strongly depended on electrochemical conditions. The SBH values exhibited a strong correlation with the particle distribution, leading to a high SBH value of 0.86 eV under the condition of the most uniform distribution of the smallest particles. The result is discussed from the viewpoint of the disorder-induced gap state (DIGS) model.
Highly-Selective Dry Etching of InAlAs Over InGaAs Assisted by ArF Excimer Laser with Cl2 Gas
Authors: Takazawa Hiroyuki , Takatani Shinichiro
Published: October 2002

Highly selective etching of InAlAs over InGaAs was observed by
irradiation with a 193-nm ArF excimer laser in a Cl2 atmosphere. The
etching rate of InAlAs relative to that of InGaAs increased as the laser
fluence decreased and the Cl2 pressure increased, and the highest observed
etching rate ratio exceeded 70. The result was compared with the case of
etching with HBr gas, where no enhancement of InAlAs etching was
observed. It is speculated that the very fast InAlAs etching rate is due to the
fast Al reaction and desorption, which introduces new reactive sites on the
surface.
Schottky Characteristics of InAlAs Grown by Metal-Organic Chemical Vapor Deposition
Authors: Ohshima Tomoyuki , Moriguchi Hironobu , Shigemasa Ryoji , Goto Shu , Tsunotani Masanori , Kimura Tamotsu
Published: October 2002

Schottky characteristics of InAlAs grown by metal-organic chemical vapor deposition
(MOCVD) have been evaluated. InAlAs Schottky characteristics are strongly affected by
MOCVD growth temperature. The reverse current of InAlAs grown at 700°C is more than
one order of magnitude larger than that at 750°C. From deep-level transient spectroscopy
(DLTS) measurements, electron traps with activation energies of 0.45, 0.33 and 0.15 eV have
been observed in InAlAs grown at 700°C. The results of C-V, Hall and secondary ion mass
spectrometry (SIMS) measurements suggest that the trap is acceptor-type and seems to be
related not to impurities but to intrinsic defects. The mechanism of the large reverse current in
InAlAs grown at 700°C is believed to be due to the conduction through the trap.
Low-Noise Bias Reliability of AlInAs/GaInAs Modulation-Doped Field Effect Transistors with Linearly Graded Low-Temperature Buffer Layers Grown on GaAs Substrates
Authors: Wakita Arlene , Rohdin Hans , Robbins Virginia , Moll Nick , Su Chung-Yi , Nagy Avelina , Basile David
Published: October 2002

The low-noise bias reliability of 0.1 µm T-gate Al0.48In0.52As/Ga0.47In0.53As modulation-doped field effect transistors (MODFETs), grown on GaAs was investigated. Al0.48In0.52As/Ga0.47In0.53As MODFETs were grown on mismatched GaAs substrates by the insertion of a compositionally linearly-graded low-temperature buffer (LGLTB) layer. Transmission electon microscopy (TEM) analysis of the layers indicates that the majority of the defects are confined to the buffer layer. Although the LGLTB layer is highly defective, there is no indication that the low-bias reliability of these devices is compromised. MODFETs with a LGLTB layer show reliability under high temperature operating life (HTOL) tests at a drain bias of 1 V and 200 mA/mm, comparable to reported MODFETs grown lattice-matched to InP. The extrapolated mean-time-to-failure (MTTF), based on the drift of the zero-gate bias current, I
dss, at temperatures of 200 to 240°C, exceeds 106 h at a channel temperature of 125°C. The drift in I
dss arises primarily from a positive shift in threshold voltage. The low-bias R
d degradation behavior of these devices is also similar to devices grown on InP.
Impact Ionization Effects on the Microwave Performance of InAs Channel Heterostructure Field-Effect Transistors: the Role of Channel Quantization
Authors: Bolognesi Colombo R. , Dvorak Martin W. , Chow David H.
Published: October 2002

The shrinking channel energy gaps in millimeter-wave heterostructure
field-effect transistors (HFETs) make the devices more susceptible to
impact ionization. Until recently, the effects of impact ionization on the
microwave performance of narrow bandgap channel HFETs have largely been
ignored. We studied the effects of impact ionization and quantum
confinement on the microwave characteristics of narrow bandgap InAs/AlSb
millimeter-wave HFETs. We systematically varied the level of impact
ionization in HFETs through channel quantization and bias conditions, and
compared the microwave behavior of InAs/AlSb HFETs (with different quantum
well widths) to that of conventional GaAs metal semiconductor field effect transistors (MESFETs) fabricated to provide a
low ionization benchmark. The observed trends in the S- and Y-parameter
data enable us to identify the physical effects of impact ionization on the
microwave behavior of narrow-gap channel HFETs. We found that field effect transistor (FET)
equivalent circuit models are grossly inadequate when InAs channel HFETs
are operated under high impact ionization bias conditions.
Design and Fabrication of a Waveguide Photodiode for 1.55-µm-Band Access Receivers
Authors: Takeuchi Takeshi , Nakata Takeshi , Tachigori Masashi , Makita Kikuo , Taguchi Kenko
Published: October 2002

A waveguide photodiode that can be used in 1.55-µm-band access receivers
was designed and fabricated. We simulated the optical coupling characteristics,
focusing especially on those related to the input spot size and for waveguide-layer
structure. The results clearly showed that both high efficiency and high tolerance can
be obtained in an optimized symmetric structure used with a hemispherically ended
fiber. The fabricated device, optimized on the basis of the simulation, showed excellent
characteristics such as an external quantum efficiency of more than 95% and a
coupling tolerance of 6.5 µm in the vertical direction.
Carrier Transport Effects in 1.3 µm Multiple Quantum Well InGaAsP Laser Design
Authors: Silfvenius Christofer , Landgren Gunnar , Marcinkevicius Saulius
Published: October 2002

We have investigated the influence of
the barrier height on the
performance of InGaAsP MQW lasers emitting at 1.3 µm via
simulations, direct hole transport
time measurements and laser
evaluation. The results from the simulation showed
that very high
barriers result in an increase in hole and electron
concentrations at
the p-side of the multiple quantum well (MQW). This leads to a severe
increase in the Auger recombination rate. The
measured hole transport
time is clearly dependent on the barrier
height in the MQW. Metal
organic vapour phase epitaxy fabricated lasers with up to twelve
periods and optimised barrier heights showed
internal efficiency
values above 95%, internal losses
below 10 cm-1, threshold
densities as low as 60 Acm-2/well and T
0
values as high as
79 K in the 20–80°C temperature range.
Our conclusion is
that attention should be given to the valence band carrier
distribution when designing low threshold,
high optical output MQW
lasers suitable for elevated temperature operation.
Surface-Grating Distributed Bragg Reflector Lasers with Deeply Etched Grooves Formed by Reactive Beam Etching
Authors: Oku Satoshi , Kondo Susumu , Noguchi Yoshio , Hirono Takuo , Nakao Masashi , Tamamura Toshiaki
Published: October 2002

Two surface-grating distributed Bragg reflector (DBR) lasers, one using a 1.55-µm-wavelength InP-based material system and one using a 0.98-µm-wavelength GaAs/AlGaAs
material system, were made using the same reactive beam etching technique following single-step
growth of the layer structure for the lasers. A 800-nm-deep grooved grating with a 240 nm period
for 1.55-µm-wavelength first-order diffraction and one with a 150 nm period for 0.98-µm-wavelength first-order diffraction were formed using electron-beam lithography and Br2-N2
mixed-gas reactive beam etching. Single-longitudinal-mode operation with a side-mode
suppression ratio of over 27 dB was obtained for both lasers; the output power was more than 15 mW for the 0.98-µm one. Between 15 and 55°C, the measured temperature dependence of the
lasing wavelength for both lasers was about 0.1 nm/°C, which is one-fifth of the dependence of a
Fabry-Perot-type laser. The performance of these lasers indicates the wide applicability of the
present etching technique to the fabrication of various
wavelength-selective devices.
New Low-Temperature Processing of Metalorganic Chemical Vapor Deposition-Bi4Ti3O12 Thin Films Using BiOx Buffer Layer
Authors: Kijima Takeshi , Matsunaga Maho Ushikubo andHironori
Published: October 2002

We have developed a new buffer layer structure to form Bi4Ti3O12 thin films using
the metalorganic chemical vapor deposition (MOCVD) method at low temperature.
We confirmed that the BiO
x
buffer layer effectively lowers the crystallization
temperature and controls the composition of Bi4Ti3O12 thin films. We have succeeded
in fabricating Bi4Ti3O12 films at 400°C with good crystallinity and ferroelectric
properties. Furthermore, we found that the film orientation is varied from the c-axis to
the (117) preferred orientation with an increasing Bi/Ti composition ratio in thin films.
The 120 nm-thick films fabricated at 400°C showed a remanent
polarization P
r of 1.9 µC/cm2 and a coercive field E
c of 55 kV/cm for the film with c-axis preferred
orientation and 8.2 µC/cm2 and 90 kV/cm for the film with (117) preferred orientation,
respectively.
Annealing Behavior of Light Scattering Tomography Defect in the Denuded Zone of Si Wafers
Authors: Furukawa Jun , Kida Michio , Shimanuki Yasushi
Published: October 2002

Light scattering tomography defects (LSTDs) have been non-destructively detected in bulk and near the surface of a Si wafer by Brewster
angle illumination of infrared light scattering tomography (IR-LST). We
investigated the annealing behavior of grown-in LSTDs that exist in a layer of
0 to about 20 µm depth from the wafer surface. Grown-in LSTDs were
detected before annealing. Annealing behavior of such grown-in LSTDs was
studied by the three-step annealing to form the denuded zone (DZ) of about 40 µm. As a result, the LSTDs mostly remained in the DZ after the three-step
annealing. However, the change in the scattering intensity of the grown-in
LSTDs was detected. This change suggests that the volume and/or structure
was changed by the annealing treatment.
Picosecond Time-Resolved Spectroscopy of Exciton Systems in CuGaS2 Bulk Single Crystals
Authors: Kunihiko Tanaka Kunihiko Tanaka , Hisao Uchiki Hisao Uchiki , Seishi Iida Seishi Iida
Published: October 2002

The decay times of bound-exciton emissions in CuGaS2 bulk crystals grown by iodine transport were measured by picosecond time-resolved spectroscopy as a function of temperature. The CuGaS2 crystals examined in this study showed two bound-exciton emission lines at 2.493 and 2.496 eV at low temperatures. Experimental results were analyzed with rate equations on the exciton kinetics using two models of free-exciton oscillator strength: strength per excitonic volume and strength per CuGaS2 molecule. Reasonable values of capture center densities and capture cross sections for the free exciton for the exciton-binding centers were obtained when using the oscillator strength per free-excitonic volume. The capture cross sections were ∼10-14 cm2 and the capture center densities were ∼1016 cm-3.
Molecular Beam Epitaxial Growth of ZnSe Films on Vicinal GaAs(110) Substrates
Authors: Maehashi Kenzo , Morota Naohiko , Nakashima YasuhiroMurase
Published: October 2002

We have investigated ZnSe epitaxial layers grown by molecular beam
epitaxy on vicinal GaAs(110) substrates using reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM) and photoluminescence (PL).
ZnSe films on vicinal GaAs(110) surfaces misoriented 6° toward (111)A show poor
crystal quality and rough surface morphology with (111) facets. On the other hand,
RHEED and AFM observations reveal that ZnSe growth proceeds in a layer-by-layer
fashion on vicinal GaAs(110) surfaces misoriented 6° toward (111)B and that
the surfaces consist of regular arrays of monoatomic steps. The PL spectra are
dominated by the near-band-edge emission.
Adsorption of H on the Ge/Si(001) Surface as Studied by Time-of-Flight Elastic Recoil Detection Analysis and Coaxial Impact Collision Ion Scattering Spectroscopy
Authors: Fuse Takashi , Ryu Jeong-Tak , Fujino Toshiaki , Inudzuka Katsuhiko , Katayama Mitsuhiro , Oura Kenjiro
Published: October 2002

We have used time-of-flight elastic recoil detection analysis (TOF-ERDA)
and coaxial impact-collision ion scattering spectroscopy (CAICISS) to
investigate the structural changes of the Ge/Si(100) surface caused by atomic
hydrogen adsorption. The following conclusions have been reached. (1) When
the Ge(1 ML)/Si(001) surface is exposed to atomic hydrogen at room
temperature, the saturation coverage of hydrogen is slightly less than that
for a clean Si(001) surface. (2) The desorption curve of hydrogen for this
surface showed that the topmost layer of the surface is covered by about 0.45 ML of Ge atoms intermixed with Si atoms, and the rest of the 1 ML of Ge
atoms are incorporated in the bulk Si layer. (3) Upon initial adsorption of
hydrogen, the asymmetry of the Ge dimer is removed, forming the symmetric
Ge dimer with a slightly expanded intradimer bond length.
Measurements of Electroluminescence Intensity Distribution in the Direction of Gate Width of n+ Self-Aligned Gate GaAs Metal-Semiconductor Field-Effect Transistors
Authors: Hiroyuki Niwa Hiroyuki Niwa , Yutaka Ohno Yutaka Ohno , Shigeru Kishimoto Shigeru Kishimoto , Koichi Maezawa Koichi Maezawa , Takashi Mizutani Takashi Mizutani , Hajime Yamazaki Hajime Yamazaki , Toru Taniguchi Toru Taniguchi
Published: October 2002

We studied electroluminescence (EL) intensity distributions in the direction of gate width of n+ self-aligned gate GaAs metal-semiconductor field-effect transistors (MESFETs). Nonuniform EL was observed along the gate-width direction, suggesting the nonuniform high-field formation in the direction of the gate. It has also been found that the EL at the source side shows gentler distribution than that at the drain side. These features suggest that the nonuniform hole distribution generated by impact ionization at the drain side becomes gradual during the process of their flow into the source and gate electrodes.
Electron Paramagnetic Resonance and Luminescence Study of Sol–Gel Derived YAG:Cr Powder
Authors: Lo Jun-Ren , Ezhilvalavan S. , Tseng Tseung-Yuen
Published: October 2002

Electron paramagnetic resonance (EPR) and luminescence
studies were carried out for the sol–gel-derived YAG:Cr powders
subjected to three kinds of heat treatment processes. The results
show that powders processed using the two-step heat treatment
process with the addition of 20 wt% LiCl and by direct heat treatment
at 1500°C exhibit good luminescence
properties. The emission spectrum for the powders obtained by the
two-step process shows the R-line at 688 nm, whereas the powders
directly heat treated at 1500°C
display an additional R-line of Al2O3:Cr at 694 nm. EPR
measurements show that the presence or absence of absorption peaks
depends on the Cr3+ environment in the host lattice resulting from the
different methods of heat treatment of the powder. The EPR spectra
of YAG:Cr3+ phosphors were interpreted to indicate both Cr3+ single
ion and Cr3+–Cr3+ pair (with spin three) transitions.
Nonsteady-State Photovoltaic Current and Photoinduced Domain Switching in Poled (Pb0.85La0.15)TiO3 and BaTiO3 Ferroelectric Ceramics
Authors: Choi Dong-Gu , Kim Sung-Ryul , Choi Si-Kyung
Published: October 2002

In (Pb0.85La0.15)TiO3 and BaTiO3 ferroelectric ceramics under illumination in the absence of an external
electric field, we observed that photovoltaic current increased with illumination time. On the basis of the
absence of pyroelectric current just after light-off and the acoustic emission (AE) signals detected during
illumination, the nonsteady-state photovoltaic current behavior was attributed to the increase in remanent
polarization, related to the increase in spontaneous polarization, and photoinduced domain switching, both of
which resulted from the space charge field established by photoexcited electrons trapped at the grain
boundaries. The influence of the poling field on the photoinduced domain switching activity could be
explained in terms of the mechanical strain energy, which acted as the energy barrier for domain wall motion,
and the energy associated with the space charge field which stimulated domain wall motion.
Electron Energy-Loss Spectroscopy Study of the Metal-Insulator Transition in (V1-xCrx)2O3 (x=0.012)
Authors: Hiroyuki Abe Hiroyuki Abe , Masami Terauchi Masami Terauchi , Michiyoshi Tanaka Michiyoshi Tanaka , Shik Shin Shik Shin
Published: October 2002

Electron energy-loss spectra of (V1-x
Cr
x
)2O3 (x=0.012)
at the antiferromagnetic insulating (AFI), paramagnetic metallic (PM) and
paramagnetic insulating (PI) phases have been measured
using a high-resolution transmission
electron energy-loss spectroscopy (EELS) microscope.
The changes in the EELS spectra
at the transition from the PM phase to the AFI phase are interpreted
in a similar manner to the case of V2O3
[Jpn. J. Appl. Phys. 37 (1998) 584].
The change in the electronic structure
at the transition from the PM phase to the PI phase (Mott transition)
was revealed for the first time.
A sharp peak observed at 1.0 eV in the PM phase
did not appear in the PI phase.
The t
2g peak of
the O 1s → V 3d(t
2g) EELS spectra shows
an energy increase of 0.5 eV
at the transition from the PM phase to the PI phase.
This increase is interpreted to occur by
the splitting of the bonding e
g
π band,
which is partially filled in the PM phase,
into the fully occupied lower band and the unoccupied upper band,
and by the lifting of the unoccupied band to
an energy higher than the Fermi level in the PM phase.
The t
2g peak also shows a decrease in intensity
but an increase in the full width at half-maximum (FWHM) at the transition.
The decrease in intensity occurs due to
the decrease of the hybridization of the V 3d with the O 2p orbitals
resulting from an increase of the V–O distance.
The increase in the FWHM results from the lifting of the a
1g
* band
due to the decrease of the lattice constant c
H and
the splitting of the e
g
π and e
g
π* bands
each into two bands due to electron correlation.
Effects of Electric Double Layer and Space Charge Polarization by Plural Kinds of Ions on Complex Dielectric Constant of Liquid Crystal Materials
Authors: Sawada Atsushi , Tarumi Kazuaki , Naemura Shohei
Published: October 2002

The complex dielectric constant of a liquid crystal material, 4-cyano-4′-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The
anomalous increasing behavior was analyzed using an equivalent circuit which
takes two kinds of contributions into account: one is from the electric double layer
and the other is from the space charge polarization. It was found by numerical
calculations that these two effects exhibit different dependences of dielectric
dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge
polarization, the experimental results were best fitted by the calculated results
with five kinds of ions in terms of the diffusion coefficient. These measurements
can be applied to a precise determination of the attributes of plural kinds of ions,
such as the diffusion coefficient and the number density.
A Proposed Organic-Silica Film for Inter-Metal-Dielectric Application
Authors: Satoshi Sugahara Satoshi Sugahara , Koh-ichi Usami Koh-ichi Usami , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

An organic-silica film has been proposed, where a short alkylene group is substituted for an oxygen atom in the silicon-dioxide matrix structure. This film is expected to have not only low dielectric constant but also good thermal conductivity and adhesion strength. The ab-initio molecular orbital calculation reveals that oxidation resistance is improved in the film. Preliminary experimental results are also presented.
Surface Acoustic Wave Sensors on Proton-Exchanged Z-Cut LiNbO3
Authors: Shen Chi-Yen , Shen Yu-Tang , Horng Richard S.
Published: October 2002

Waveguides provide several advantages such as acoustic and optical
beam confinement, prolongation of delay time, and high acoustic
intensity for the acoustic devices. Using proton exchange (PE) with
benzoic acid, we have investigated the surface acoustic wave (SAW)
properties of a PE waveguide using Z-cut LiNbO3. With this tight
energy confinement, the acoustic waveguide structure enables the
guided SAW to be in a suitable mode for dilute electrolyte sensing.
Furthermore, it is noteworthy that the dielectric constant of a PE layer
can be deduced from the critical conductivity.
Electrostrictive Phenomena Associated with Polarization Reversal in Ferroelectric Polymers
Authors: Yuki Toshinao , Yamaguchi Etsuro , Koda Tomonori , Ikeda Susumu
Published: October 2002

The electrostriction effect of ferroelectric vinylidene fluoride (VDF) and
trifluoroethylene copolymers was studied by measuring their dimensional variation under an
external electric field changing beyond a coercive electric field. The relationship between
strain and polarization for the copolymer which includes a 54 mol% VDF reveals a parabolic
electrostriction relationship over the entire measurement range of the strain-polarization
relationship. The relationship for the copolymer which includes a 73 mol% VDF, however,
deviates from the parabolic relationship. The result is discussed in terms of the
thermodynamics of a ferroelectric phase transition. Furthermore, the origin of the
ferroelectricity of these copolymers is discussed.
Collective Molecular Motion during V-Shaped Switching in a Smectic Liquid Crystal
Authors: Byoungchoo Park Byoungchoo Park , San-seong Seomun San-seong Seomun , Michi Nakata Michi Nakata , Masayoshi Takahashi Masayoshi Takahashi , Yoichi Takanishi Yoichi Takanishi , Ken Ishikawa Ken Ishikawa , Hideo Takezoe Hideo Takezoe
Published: October 2002

The molecular motion during V-shaped
switching in a homogeneously aligned smectic C*-like liquid
crystal (LC) cell has been investigated by measuring the effective optical
anisotropy Δn
eff,
apparent tilt angle θapp, switching current, and second-harmonic
generation and comparing them with the simulated results based on two
extreme models, i.e., random model and collective model, where molecules
switch randomly and collectively, respectively. The comparison revealed
that the collective switching motion of LC molecules
is more reasonable than the random motion. Moreover, it was also
confirmed that the observed infrared
absorption anisotropy of the phenyl stretching mode due to LC
molecular distributions strongly supports the collective model.
From these results, it was demonstrated that LC molecules
do not switch randomly but all the LC molecules rotate
collectively on a cone under the driving field.
Gas-Source Molecular Beam Epitaxial Growth of In1-xGaxP on GaAs Using Tertiarybutylphosphine
Authors: Sai Hironobu , Fujikura Hajime , Hasegawa Hideki
Published: October 2002

A systematic study of growth was made for gas-source molecular beam
epitaxial (GSMBE) growth of In1-x
Ga
x
P using tertiarybutylphosphine (TBP), in
order to establish the conditions required to grow high-quality In1-x
Ga
x
P layers on
GaAs(100) substrates. To clarify the effect of the P
2 supply rate on growth, a
special effort was made to increase the P
2 supply by modifying the structure of the
conventional cracking cell. The alloy composition and growth rate depended
strongly on the type of cracking cell, growth temperature and TBP flow rate. The
growth was group-III-limited at low growth temperatures, but became limited by
thermal desorption of phosphorus at higher temperatures. The use of a high-efficiency cracking cell was found to be important for suppressing phosphorous
evaporation and growing high-quality InGaP layers with controlled thickness and
alloy compositions. Optimized growth led to an excellent photoluminescence (PL)
property with a narrow peak width of 15.5 meV at 77 K and 38 meV at 300 K.
These are comparable to the best data reported so far for InGaP layers grown by
any method.