bluuebunny/crossref_metadata_2025 huggingface dataset:
Possibility for the Discrimination of Submonolayer InAs and GaAs Grown on Tilted GaAs Substrate
Authors: Noh Joo-Hyong , Asahi Hajime , Hiromichi Watanabe Hiromichi Watanabe , Shun-ichi Gonda Shun-ichi Gonda
Published: October 2002

InAs submonolayers grown on tilted (001) GaAs substrates by gas source migration enhanced epitaxy are studied by plan-view scanning tunneling microscopy and scanning tunneling spectroscopy. Two contrasting areas are observed on the terrace. The bright stripe (InAs area) width is observed to increase with the amount of In supplied during growth. The difference between the contrasting areas is also observed in the I-V curve; the slope d I/d V is dependent on the bright and dark areas and shows the same values in each area, although the onset voltage for the current rise is the same in both InAs and GaAs regions.
High-Tc Superconductor-Insulator-Superconductor Heterostructures with Highly Resistive Insulator Layers
Authors: T. Frey T. Frey , J. Mannhart J. Mannhart , J. G. Bednorz J. G. Bednorz , E. J. Williams E. J. Williams
Published: October 2002

Trilayers in which a dielectric or ferroelectric film such as SrTiO3, BaTiO3 or Ba

x

Sr1-
x

TiO3 separates two layers of a high-T
c superconductor are required for many device applications of high-T
c materials. To clarify the mechanism limiting the insulation properties of the insulating layer, the microstructure of such samples was analyzed using transmission electron microscopy. These studies suggest that diffusion along threading dislocations or along grain boundaries in the insulating layer lowers its resistivity. Substitution of the insulating monolayer with a bilayer increases the resistivity from ≃1011 to 3×1013 Ω· cm (at 2×105 V/cm, below 100 K). To our knowledge, this is by far the highest resistivity achieved in such heterostructures.
Polarity-Dependent Multicolor Organic Electroluminescent Device
Authors: Masayoshi Yoshida Masayoshi Yoshida , Akihiko Fujii Akihiko Fujii , Yutaka Ohmori Yutaka Ohmori , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

A multicolor organic electroluminescent (EL) device utilizing poly(9, 9-dihexylfluorene) (PDHF) and N, N'-bis(2, 5-di-tert-butylphenyl)-3, 4, 9, 10-perylenedicarboximide (BPPC) has been successfully realized. The multicolor EL device emits either blue green or red light depending on the polarity of applied voltage. Both emissions have comparable intensity at the same injection current. By driving with AC field both blue green and red emission can be observed.
Multiple-Peaked Structure in the Nonlinearity Coefficient of ZnO Varistors
Authors: M. Bartkowiak M. Bartkowiak , G. D. Mahan G. D. Mahan , F. A. Modine F. A. Modine , M. A. Alim M. A. Alim
Published: October 2002

Computer simulations of the current conduction through the granular microstructure of polycrystalline ZnO varistors are used to explain the multiple-peaked structure observed in the nonlinearity coefficient measured as a function of voltage for low-voltage varistors and for varistors with microelectrode contacts on their surface. Two-dimensional Voronoi networks with random mixtures of electrically nonlinear and ohmic elements are used to model the varistors. It is shown that the statistical dispersion of the grain sizes has no significant effect on the nonlinearity coefficient. The multiple-peaked structure is caused by a small amount of randomly distributed grain boundaries with ohmic behavior, i.e., linear current-voltage characteristics of low resistivity. The observed reduction of the maximum nonlinearity coefficient of polycrystalline varistors, relative to that of isolated grain boundaries, is attributed to the presence of varistor microjunctions with poor nonlinearity.
Crystallization of Boric Acid on Low-K Glass+ Ceramic Green Tapes
Authors: Jau-Ho Jean Jau-Ho Jean
Published: October 2002

Crystallization at room temperature on the surface of low-k glass+ceramic green tapes, containing a low-softening-point borosilicate glass and a high-softening-point high silica glass has been investigated. Results of diffuse reflectance Fourier transform infrared (FTIR) and Raman microprobe spectra show that the crystals are boric acid, formed by reaction of the boric oxide in the borosilicate glass with water in an ambient atmosphere. A faster and greater degree of crystallization is observed with increased level of relative humidity in the ambient atmosphere. To minimize the formation of boric acid crystals on the green tapes, a relative humidity of 15% or less is required.
Surfactant-Induced Bond Strengthening in As-Grown Film Surfaces
Authors: Nakamura Jun , Konogi Hidekazu , Osaka Toshiaki
Published: October 2002

The role of surfactant (Sb) in the two-dimensional (2D) growth of Ge films on Sb-adsorbed Si(111) surfaces is investigated using the discrete variational (DV)-Xα cluster method. The results show that the Sb surfactant strengthens bonds between Ge atoms of the film surface, to the extent of those in bulk Ge, and enables them to realize an sp3-like configuration. This indicates why the critical thickness is increased in this system: the surfactant-induced bond strengthening renders the film surface hard like that of bulk Ge, induces dislocations to nucleate at the surface, and enables the Ge film to grow in a defect-free state, as expected based on the self-annihilation mechanism proposed by Horn-von Hoegen et al.. [M. Horn-von Hoegen et al.. Phys. Rev. Lett. 67 (1991) 1130].
The Morphology of Lamellar C70 Single Crystals as Studied by Atomic Force Microscopy
Authors: Jiang Lei , Iyoda Tomokazu , Kino Nobuhiro , Kitazawa Koichi , Hashimoto Kazuhito , Fujishima Akira
Published: October 2002

C70 single crystals were grown using the vapor phase transport technique. Lamellar growth was evident on the surfaces of some crystals. The bulk structure of these crystals was confirmed to be hexagonal closed-packed (hcp) by X-ray diffraction. The surface morphology of the lamellar crystals was investigated using atomic force microscopy (AFM). In the lamellar growth areas, micrometer sized (0001), (10*BAR*1*BAR*0), and (01*BAR*1*BAR*0) faces were observed in low resolution AFM images. For the first time, AFM images have been obtained for all of these faces. The AFM images revealed that lamellar growth originates in regions in which three types of faces can co-exist near the edges of the crystal. A monolayer-spreading growth mechanism was inferred from the layered structure images. High resolution images were obtained on the (0001) and the (10*BAR*1*BAR*0) faces. It was observed that the molecules on the (0001) face were arranged in a slightly distorted hexagonal arrangement, with an average nearest-neighbor distance a=10.5±0.3 Å. On the (10*BAR*1*BAR*0) face, the molecules were arranged in a distorted rectangular unit (with α=75°±3°), with a=10.5±0.3 Å and c=19.0±0.3 Å. On both faces, a long-axis disorder of the surface C70 molecules was suggested. The surface molecular arrangements were able to be resolved, exhibiting a distorted hcp structure.
Four-Domain Twisted Nematic Liquid Crystal Display Fabricated by Two Alignment Layers with Low and High Pretilt Angles
Authors: Chen Jianmin , Bos Philip J. , Johnson David L. , Kelly Jack R. , Kim Nam-Deog , Crow John
Published: October 2002

A new 4-domain (4-D) twisted nematic (TN) configuration which requires two different alignment layers with different pretilt angle is proposed. The detail processes for realization of this 4-D TN are given. The optical simulation of the viewing angle characteristics shows this 4-D TN display has a homogenous viewing angle feature. The optical averaging effect from different subpixels is confirmed by our testing cells.
A New Metallic Langmuir-Blodgett Film Formed with BO 2-(MeO) 2TCNQ, where BO is Bisethylenedioxytetrathiafulvalene and (MeO)2TCNQ is Dimethoxytetracyanoquinodimethane
Authors: Kazuyoshi Ogasawara Kazuyoshi Ogasawara , Takehiko Ishiguro Takehiko Ishiguro , Sachio Horiuchi Sachio Horiuchi , Hideki Yamochi Hideki Yamochi , Gunji Saito Gunji Saito
Published: October 2002

Based on the unique nature of bisethylenedioxytetrathiafulvalene (BO), a stable, highly conductive Langmuir-Blodgett film was developed using a charge-transfer (CT) complex of BO and dimethoxytetracyanoquinodimethane ((MeO)2TCNQ). A clear negative temperature-derivative of the conductivity was observed down to 180 K, indicating the establishment of the macroscopic metallic conduction. The paramagnetic spin susceptibility indicates that the metallic phase is retained down to 50 K and the CT complex molecules are highly oriented in the stacking direction.
Effects of GaAs-Surface Roughness on the Electron-Beam Patterning Characteristics of a Surface-Oxide Layer
Authors: Tomonori Ishikawa Tomonori Ishikawa , Nobuyuki Tanaka Nobuyuki Tanaka , Máximo López Máximo López , Isamu Matsuyama Isamu Matsuyama
Published: October 2002

We have studied the effects of the roughness of a GaAs epitaxial surface on the characteristics of a surface oxide layer, which is used as a resist-mask in “ in situ electron-beam (EB) lithography”. The oxide layer formed on a microscopically rough surface resulted in degraded threshold characteristics of EB patterning and in an indented pattern edge. On the other hand, when we formed it on a flat epitaxial surface, obtained by step-flow growth using a misoriented substrate, the threshold characteristics were remarkably improved, and the resulting pattern exhibited a sufficiently sharp edge. These improvements are helpful for fabricating nanostructures by in situ EB lithography.
Nanolithography Using Fullerene Films as an Electron Beam Resist
Authors: Tetsuya Tada Tetsuya Tada , Toshihiko Kanayama Toshihiko Kanayama
Published: October 2002

Electron beam (e-beam) irradiation has been found to reduce the dissolution rate of evaporated C60 films in organic solvents such as monochlorobenzene, which shows that this material acts as a negative e-beam resist with a sensitivity of 1×10-2 C/cm2. It has higher dry-etch durability than conventional novolac resists. Its applicability to nanofabrication has been demonstrated by fabricating Si pillars of 20–30 nm diameter using electron cyclotron resonance microwave plasma etching and dot patterns defined in the C60 film as etching masks.
Polysilicon Thin-Film Transistors Processed at Low Temperature ( \Leq600°C) Using Solid-Phase Crystallization in Wet Oxygen Atmosphere
Authors: Hamada Hiroki , Sasaki Akihumi , Yuji Okita Yuji Okita , Tatuhiko Niina Tatuhiko Niina
Published: October 2002

The spin density and oxygen concentration of polysilicon films have been successfully reduced using a novel solid-phase-crystallization (SPC) method in an ambient of wet oxygen. The threshold voltage (V
th), subthreshold swing (S) and field-effect mobility (µ FE) for thin-film transistors (TFTs) processed at ≦600° C using the polysilicon films were 2.0 V, 0.27 V/dec, and ∼35 cm2/ V·s, respectively. This performance was achieved with one-third less plasma hydrogeneration time than that of the conventional SPC method in an ambient of nitrogen.
A Possible Three-Terminal Amplifier Device in the Terahertz Frequency Range Using Photon-Assisted Tunneling
Authors: Masahiro Asada Masahiro Asada
Published: October 2002

A new electron device with nanometer-thick multilayer heterostructure is proposed for amplification of an electromagnetic wave. The device is composed of the input part utilizing photon-assisted tunneling and the output part utilizing radiation from a charge density wave modulated at the input. A simple analysis shows that amplification up to the terahertz frequency range is possible in the device.
Photoconductive Behavior in Smectic A Phase of 2-( 4'-Heptyloxyphenyl)-6-Dodecylthiobenzothiazole
Authors: Masahiro Funahashi Masahiro Funahashi , Jun-ichi Hanna Jun-ichi Hanna
Published: October 2002

A new liquid crystalline photoconductor, 2-(4'-heptyloxyphenyl)-6-dodecylthiobenzothiazole exhibiting a smectic A (SmA) phase between 90° C and 100° C was synthesized and its photoconductive behavior was characterized by steady-state current-voltage measurements under ultraviolet illumination. A large photocurrent with a clear response to the illumination is observed in SmA and isotropic liquid phases in contrast to a very small photocurrent in the polycrystalline phase. The experimental results suggest electronic conduction in the SmA phase of calamitic liquid crystal.
Studies of the Bistability of Highly Twisted Nematics
Authors: Li Jianlin , Charles D. Hoke Charles D. Hoke , Philip J. Bos Philip J. Bos
Published: October 2002

The bistable electro-optic effect of highly twisted nematic liquid crystals was studied. A numerical relaxation technique was used to minimize the free energy density of a liquid crystal medium. The director configurations at an applied field, especially the mid-cell director, may be significantly different depending on the initial conditions. The elastic energy of the liquid crystal medium was used to describe its bistability. The effects of cell twist angle, elastic constants, thickness to pitch ratio, dielectric parameter, and surface pretilt angle were studied.
InGaN-Based Multi-Quantum-Well-Structure Laser Diodes
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Hiroyuki Kiyoku Hiroyuki Kiyoku , Yasunobu Sugimoto Yasunobu Sugimoto
Published: October 2002

InGaN multi-quantum-well (MQW) structure laser diodes (LDs) fabricated from III-V nitride materials were grown by metalorganic chemical vapor deposition on sapphire substrates. The mirror facet for a laser cavity was formed by etching of III-V nitride films without cleaving. As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs produced 215 mW at a forward current of 2.3 A, with a sharp peak of light output at 417 nm that had a full width at half-maximum of 1.6 nm under the pulsed current injection at room temperature. The laser threshold current density was 4 kA/cm2. The emission wavelength is the shortest one ever generated by a semiconductor laser diode.
Fabrication of Multilayered Conducting Polymer Heterostructure by Self-Assembly Technique and Its Optical and Electrical Properties
Authors: Tsuyoshi Kawai Tsuyoshi Kawai , Takahiro Yamaue Takahiro Yamaue , Kazuya Tada Kazuya Tada , Mitsuyoshi Onoda Mitsuyoshi Onoda , Sung-Ho Jin Sung-Ho Jin , Sam-Kwon Choi Sam-Kwon Choi , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

A using multilayered conducting polymer heterostructure is fabricated by the self-assembly technique with a negatively charged conducting polymer, poly(3-α-carboxylmethylthiophene), and a positively charged conducting polymer, poly(dihexyldipropargyl ammonium bromide), and its optical and photovoltaic properties are studied. Photoluminescence from the positively charged conducting polymer is quenched markedly in the multilayered heterostructure system. The enhanced photovoltaic effect observed in a junction device with Al and ITO electrodes is explained in terms of photoinduced charge separation at the interface of conducting polymers.
Characteristics of SiOF Films Formed by Remote Plasma Enhanced Chemical Vapor Deposition with SF6 Gas
Authors: Yu Byoung-Gon , Kim Kwang-Ho , Kyung-Soo Suh Kyung-Soo Suh , Jong Tae Baek Jong Tae Baek
Published: October 2002

The dielectric SiOF films were deposited by a simple technique which was SF6 gas addition to the TEOS based and SiH4 based Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD). The deposition rate decreased with increasing of the SF6 flow rate about 30 sccm. The refractive index decreased with increasing SF6 flow rate. The etch rate decreased down to 20 sccm, while in the case of above 20 sccm somewhat increased with increasing with SF6 flow rate. The peak position of the Si–O stretching mode gradually shifts to higher wave number with increasing of the SF6 flow rate. The dielectric constant decreased to 3.3. Gap filling and planarizability of the dielectric film formed by the TEOS with SF6 gas is better than that of the films made with conventional TEOS based.
Device Characteristics of Polycrystalline Si0.84Ge0.16 Thin Film Transistors Grown from Si2H6 and GeH4 Source Gases
Authors: Kim Jin-Won , Ryu Myung-Kwan , Kim Ki-Bum , Hwang Chang-Won , Bae Byung Seong , Han Min-Koo , Sang-Joo Kim Sang-Joo Kim
Published: October 2002

Polycrystalline Si0.84Ge0.16 alloy film was made by solid phase crystallization (SPC) of an amorphous film deposited using Si2H6 and GeH4 source gases by low pressure chemical vapor deposition (LPCVD). The grain size of the film was about 540 nm and the preferred orientation was (111). Both n-channel and p-channel polycrystalline Si0.84Ge0.16 thin film transistors were successfully fabricated using a high temperature process. The field-effect mobilities of n- and p-channel devices were 13 and 29 cm2/V·s, which were improved to 33 and 38 cm2/V·s, respectively, after electron-cyclotron resonance (ECR) hydrogen plasma treatment.
Measurement of Band Discontinuity at ZnSe/GaAs Boundary Using Free Electron Laser
Authors: Nishi Kazuhisa , Ohyama Hideaki , Suzuki Toshiji , Tsuneo Mitsuyu Tsuneo Mitsuyu , Takio Tomimasu Takio Tomimasu
Published: October 2002

We investigated the band discontinuity at the ZnSe/GaAs boundary using the free electron laser internal photoemission (FEL-IPE) technique. This technique is based on photocurrent spectroscopy utilizing the tunability and intense peak power of the FEL operative in the infrared range. We have found the threshold of the photocurrent near the photon energy of 110 meV which can be identified as the band discontinuity in the ZnSe/GaAs heterojunction.
Preparation of YBa2Cu3O7-δ Thin Films by Metal-Organic Chemical Vapor Deposition Using Liquid Sources
Authors: Ito Yoshiaki , Yoshida Yutaka , Mizushima Yasuyuki , Hirabayashi Izumi , Nagai Hisashi , Takai Yoshiaki
Published: October 2002

YBa2Cu3O7-δ (YBCO) thin film was fabricated by metal-organic chemical vapor deposition (MOCVD) using newly developed liquid MO-sources (MO=metal-organic). The melting points of the MO-sources are lower than those of conventional MO-sources, and they have stable vapor pressure even in the liquid state. The MO-sources contain fluorine; however, when water was added to the flowing oxygen gas, the fluorine-to-oxygen ratio of the films was reduced to less than 0.08 at% as determined by secondary ion mass spectroscopy (SIMS). The reproducibility of the composition and the superconducting properties of the prepared films was excellent compared to that of films fabricated using conventional MO-sources.
Optical Signal Inverter Derived from Negative Nonlinear Absorption Effects
Authors: Maeda Yoshinobu , Seiichi Ikeda Seiichi Ikeda , Masatoshi Migitaka Masatoshi Migitaka
Published: October 2002

Using a modulated laser diode, dependence of a negative nonlinear absorption effect on both the wavelength and the sample length was observed in an erbium doped yttrium aluminum garnet crystal which has a four-level energy structure. The effect was seen at wavelengths of 787.4 to 788.6 nm in excited state absorption spectra which showed a peak corresponding to the transition from 4
I
13/2 to 2
H
11/2 in Er3+ for sample lengths greater than 2.0 mm. An optical signal inverter which had a negative input-output characteristic was realized using the negative nonlinear absorption effect.
Actual Emitting Region in Organic Electroluminescent Diodes with Multilayer Structure
Authors: Tatsuo Mori Tatsuo Mori , Kouji Obata Kouji Obata , Teruyoshi Mizutani Teruyoshi Mizutani
Published: October 2002

The EL mechanism of organic light-emitting diodes (organic LEDs) with a multilayer structure was studied by the dye-doping method. The actual emitting region of the specimen was found to be in some, not all, of the emission layers near the cathode. It shifted from the emission layer beside the cathode to one beside the anode depending on applied current, and it extended over several emission layers with the increase of current. In addition, the EL efficiency per current density in the specimen was 1/10 lower than that in the double-layer specimen. We discussed the possibility of the effect of exciton confinement.
Study of Hydrogen Ion Bombardment Effect on the Growth of Si:H Films Prepared by Hydrogen Plasma Sputtering of Silicon
Authors: Yong SUN Yong SUN , Ryusuke NISHITANI Ryusuke NISHITANI , Tatsuro MIYASATO Tatsuro MIYASATO
Published: October 2002

Hydrogen ion bombardment effects on the growth of hydrogenated silicon films prepared by reactive hydrogen plasma sputtering of silicon are studied by controlling the local plasma conditions near the growing film surface. It is found that the hydrogen ion bombardment affects the film growth rate by means of a balance between the hydrogen ion flux density and the coverage of film growth intermediate at the growing surface. Hydrogen ion bombardment enhances film etching for low coverage, but promotes film deposition for high coverage of film growth intermediate at the growing surface.
Highly Conductive P-Type ZnTe:As Grown by Atmospheric Metalorganic Chemical Vapor Deposition Using Trimethylarsine
Authors: Atsushi Kamata Atsushi Kamata , Hiroaki Yoshida Hiroaki Yoshida
Published: October 2002

Highly conductive p-type ZnTe was grown by atmospheric metalorganic chemical vapor deposition (MOCVD). The source materials were dimethylzinc and diisopropyltelluride. Arsenic was doped into ZnTe with trimethylarsine. The carrier concentration depended on both the growth temperature and VI/II ratio. The highest carrier concentration measured in Hall measurements was 1.3×1019 cm-3, which is the highest ever reported for MOCVD-grown ZnTe. Low-temperature photoluminescence spectra showed strong As-related bound exciton lines and donor-to-acceptor recombination lines.
New III–V Compound Semiconductors TlInGaP for 0.9 µm to over 10 µm Wavelength Range Laser Diodes and Their First Successful Growth
Authors: Asahi Hajime , Yamamoto Kazuhiko , Iwata Kakuya , Oe Shun-ichi Gonda
Published: October 2002

New III–V compound semiconductors TlInGaP (thallium indium gallium phosphide) lattice-matched to InP are proposed for 0.9 µm to over 10 µm wavelength range laser diodes and their first successful growth is reported by gas-source molecular beam epitaxy. A type-I band lineup and a larger band discontinuity in the conduction band than in the valence band are expected for their heterostructures. They also have the potential to exhibit a temperature-independent band-gap energy (wavelength), which is promising for the fabrication of lasers that can be used in wavelength division multiplexing (WDM) optical fiber communication. Grown layers exhibit (2×4) surface reconstruction and have mirror-like surfaces. Phase separation is not observed in this material system by X-ray diffraction measurement.
Shift in Threshold Voltage and Schottky Barrier Height of Molybdenum Gate Gallium Arsenide Field Effect Transistors after High Forward Gate Current Test
Authors: Kimura Tamotsu , Shigemasa Ryoji , Tomoyuki Ohshima Tomoyuki Ohshima , Seiji Nishi Seiji Nishi
Published: October 2002

The threshold voltage and the Schottky barrier height of InGaAs/AlGaAs HEMTs or GaAs MESFETs with molybdenum Schottky gates were observed to shift after high forward gate current tests, and the shift was recovered by subsequent heat treatment. Experimental results show that this phenomenon is characteristic of molybdenum Schottky gates on GaAs, and it is related to the deep traps near the interface between molybdenum and GaAs or within the GaAs channel layer. Such deep traps were introduced due to the electron irradiation effect during the electron beam deposition of the molybdenum (Mo) on GaAs. Insertion of a thin Ti layer between Mo and GaAs was found to be effective for suppressing the shift.
High-Conversion-Efficiency Solar Cell Using Fluorescence of Rare-Earth Ions
Authors: Ryouhei Nakata Ryouhei Nakata , Naoaki Hashimoto Naoaki Hashimoto , Katsuyasu Kawano Katsuyasu Kawano
Published: October 2002

An experiment was performed to obtain a high-conversion-efficiency solar cell by shifting UV-region sunlight to the visible region, in which the optical absorption and emission properties of rare-earth Eu activator ions were exploited. A thin disc of CaF2:Eu single crystal was used as an alternative to the antireflection (AR) film in a solar cell. The effectiveness of rare-earth ions was examined. Their relative efficiencies were found to be higher at Eu concentrations from 0.001 to 2 mol%, with a maximum value of 1.5 at 0.05 mol%, than those of nondoped crystal when subjected to low illuminance by a Xe-lamp-based solar simulator. For the purpose of putting the crystal to practical use as an AR film, rare-earth ions were implanted into CaF2 crystal at a dose of 1014–1015 ions/cm2 and an energy of up to 140 keV.
Orientation of Carbon Nanotubes Using Electrophoresis
Authors: Kunitoshi Yamamoto Kunitoshi Yamamoto , Seiji Akita Seiji Akita , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

Electric field orientation of carbon nanotubes has been demonstrated using electrophoresis in isopropyl alcohol. The carbon nanotubes move towards the cathode during this process. The nanotubes align along the electric field due to the anisotropy of their electrophoresis velocity. The mobility has been estimated to be higher than ∼5×10-5 cm2· V-1· s-1. The results suggest that it is possible to purify and handle carbon nanotubes using electrophoresis.
Anisotropy of Nonrubbed UV Curable Polymer Films Inducing Liquid Crystal Alignment
Authors: Rumiko Yamaguchi Rumiko Yamaguchi , Susumu Sato Susumu Sato
Published: October 2002

Nonrubbed UV curable polymer surfaces for liquid crystal alignment are made by copying the aligning function of a stretched or rubbed polyethylenterephthalate (PET) film surface. Optical anisotropy is generated and the surface topology is found to be isotropic on an alignment surface prepared using the stretched film. Both topological and optical anisotropies are generated on the surface where the rubbed PET film surface is copied. The azimuthal anchoring energy of the latter surface is larger than that of the former surface.
A Contribution of Vibrationally Excited Cl 2 Molecules to GaAs Reactive Ion Etching in Cl 2/Ar
Authors: Stanislav A. Moshkalyov Stanislav A. Moshkalyov , Munemasa Machida Munemasa Machida , Sergei V. Lebedev Sergei V. Lebedev , Delton O. Campos Delton O. Campos
Published: October 2002

The experimental results on GaAs RIE in Cl2/Ar are considered within the framework of the ion–neutral synergy model. It has been shown, that the model gives a good agreement with the etch rate data obtained for low Cl2 partial pressure, but fails at the increased chlorine percentage. A possible contribution of vibrationally excited Cl2 molecules to GaAs etch rate has been considered.
Reduction of Threshold Current Density of Wurtzite GaN/AlGaN Quantum Well Lasers by Uniaxial Strain in (0001) Plane
Authors: Masakatsu Suzuki Masakatsu Suzuki , Takeshi Uenoyama Takeshi Uenoyama
Published: October 2002

The uniaxial strain effect in the (0001) plane on the electronic and optical gain properties of wurtzite GaN/AlGaN quantum well lasers is investigated on the basis of k·p theory. In order to obtain the required physical parameters, the first-principles band calculations are used. It is found that the uniaxial strain in the (0001) plane causes much lower threshold current density than the biaxial strain does. The relation between the uniaxial strain's direction and the optical polarization is clarified as well. As a result, we predict that the uniaxial strain in the (0001) plane is one of the preferable approaches for the efficient improvement of the GaN-based lasers performance.
Preparation of Ceramics (RCa)Ba2Cu4O8 (R=Y, Ho, Er, Tm and Yb) by Conventional Solid-State Reaction
Authors: Tatsumi Masakazu , Nishi Miho , Takenori Shigeta Takenori Shigeta , Seika Yamamoto Seika Yamamoto
Published: October 2002

Bulk superconductors of Ca-doped RBa2Cu4O8 (R124, R=Y, Ho, Er, Tm and Yb) were synthesized at 1 atm oxygen pressure. Although little undoped Yb124 material was obtained by a conventional solid-state reaction method, a single-phase sample was obtained upon Ca doping. The solubility limit of Ca increased with decreasing ionic radius of R. The zero-resistant temperature (T
c0) for Ca-doped R124 increased with increasing Ca content. The highest T
c0 (=85.4 K) was obtained for the 5% Ca-doped Yb124 sample. In addition, T
c0 of undoped Yb124 ceramics was estimated to be about 80 K from the result for Ca-doped samples.
Flux Pinning and Vortex Dynamics in K3C60 Crystals
Authors: Lee Ming-Way , Shi Jen-Bin , Chun-Shan Chen Chun-Shan Chen
Published: October 2002

AC susceptibility measurements were carried out on K3C60 crystals. The complex susceptibility χ=χ′+χ′′ shows dependence on dc magnetic-field amplitude H
dc and ac amplitude h
ac. The temperature where χ′′ is maximal, T
p, exhibits a weak dependence on ac frequency f: T
p rises with increasing f. Increasing H
dc or h
ac enhances the effect. The inverse temperature, T
p
-1, roughly obeys the linear relationship T
p
-1≈-5×10-5
H
dcln
f+b(H
dc), where b is a constant and SI units are used. This is in qualitative agreement with the predictions of the thermally activated flux creep model. This suggests that in the experiment flux lines are pinned at pinning sites and ac losses are mainly due to flux pinning losses. The temperature T
p is found to obey an empirical scaling law (1-T
p/T
c)3/2≈4×10-4
H
dc[ln
(f
0/f)+25]+1.4×10-2. The scaling relationship is in good agreement with the predicted equation based on the model of thermally activated flux motion.
Doping Effect on the Electric Current and Molecular Structure of a Vinylidenefluoride-Trifluoroethylene Copolymer
Authors: Hayashi Kohtaku , Tsubakihara Hiroshi , Uichi Kubo Uichi Kubo
Published: October 2002

This paper describes the doping influence of the ionic rhodamine 6G (R6G) dye on the electric current of the Vinylidenefluoride-Trifluoroethylene (VDF-TrFE) copolymer induced by irradiation from a TEA CO2 laser. The current of the nondoped sample increases rapidly at the poling field over 0.4 MV/cm, and the current of the doped one has a point of a rapid increase lower than that of the nondoped one. The infrared spectra and the dielectric constants of the undoped and doped samples have been studied. The qualitative analysis shows that the current is affected by the ionic R6G dye.
Saturation Measurements of Electrically Detected Magnetic Resonance in Hydrogenated Amorphous Silicon Based Thin-Film Transistors
Authors: Kawachi Genshiro , Graeff Carlos F. O. , Brandt Martin S. , Stutzmann Martin
Published: October 2002

The saturational broadening of an electrically detected magnetic resonance signal in hydrogenated amorphous silicon has been observed in thin-film transistor structures. It was found that broadening of the resonance spectrum with increasing microwave power is caused by an enhanced local microwave field in the transistor due to strong coupling of the microwave field with the microstrip-like structure of the transistor. The field enhancement factor, which was estimated from saturation measurements, can reach 33 in a transistor with a channel width-to-length ratio of 500/10, demonstrating that the thin-film resonator is an effective tool for improving the detection sensitivity.
Etching of Nondiamond Carbon in Diamond Thin Films Synthesized by Hot-Filament Chemical Vapor Deposition with Ultraviolet Irradiation
Authors: Ishikawa Yutaka , Hirose Hideto Yoshimi
Published: October 2002

The etching of nondiamond carbon present in diamond thin films which were grown using the CVD method has been studied with UV irradiation in air. The etching of nondiamond carbon was accelerated by UV irradiation, and hence the temperature required was lowered from 600 °C to 250 °C. On the other hand, the temperature required to etch diamond in the film did not change even with UV irradiation. Selective etching of nondiamond carbon in diamond thin films can be achieved at temperatures between 250 °C and 550 °C. These etching effects are caused by excited atomic oxygen produced by the UV irradiation and not by the direct excitation of the film by UV irradiation.
Wire Induced Flashover as a Source of Shock Waves for Destruction of Solid Materials
Authors: Lisitsyn Igor V. , Taishi Muraki Taishi Muraki , Hidenori Akiyama Hidenori Akiyama
Published: October 2002

Explosive wire induced surface flashover is proposed and studied as a promising method for destruction of solid materials. An experimental investigation of electric parameters in this type of discharge was carried out in order to optimize fuse parameters for maximum efficiency energy transfer into the shock wave. The maximum energy input into the discharge is up to 90% of the energy stored in the capacitor bank compared to about 20% if conventional surface flashover in water is utilized. Pressure measurements with calibrated pressure transducers indicated an energy transformation efficiency into shock waves in water of 40–50%.
Thermal Expansions of Pure and Al-doped CsLiB6O10 Crystals for Nonlinear Optical Applications
Authors: Takei Humihiko , Suzuki Takuya , Mamiya Mikito , Sakai Fumiko , Koike Masayoshi , Mori Yusuke , Sasaki Takatomo
Published: October 2002

Changes in X-ray powder diffraction patterns of pure and Al-doped CsLiB6O10 (CLBO) crystals for nonlinear optics upon heating are observed between room temperature and 500°C. The crystals undergo linear elongation by about 2×10-5 deg-1 along the a-axis, and contraction by about -2×10-5 deg-5 is observed along the c-axis. Such extraordinary behavior on heating is a reflection of the structure of CLBO which costists mainly of a combination of hexagonal B3O4 rings, and a marked difference in linkage of the rings appears between the a- and c-axes. No significant changes in the thermal expansion coefficients are observed on Al-doping, though considerable expansions along the a- and c-axis are observed.
Enhanced Solid-Phase Crystallization of Amorphous Si by Plasma Treatment Using Reactive Ion Etching
Authors: Tanemasa Asano Tanemasa Asano , Katsuhide Aoto Katsuhide Aoto , Yoshihiro Okada Yoshihiro Okada
Published: October 2002

Solid-phase crystallization of amorphous Si (a-Si) films was found to be enhanced by oxygen- or nitrogen-plasma treatment prior to annealing for crystallization using a reactive ion etching system. Amorphous Si films were deposited by vacuum evaporation under ultrahigh-vacuum conditions. Plasma treatments were carried out using a conventional parallel-plate reactive ion etching apparatus. The incubation time for crystallization of a-Si was found to be greatly reduced by plasma treatment. Nitrogen-plasma treatment resulted in more enhanced crystallization than oxygen plasma. The incubation time was found to decrease with the increase of the self-bias voltage of the reactive ion etching system during plasma treatment. Impurity analysis suggests that metal atoms adsorbed during treatment at the surface of a-Si is one cause of the enhanced crystallization.
Evaluation of Double Spacer Local Oxidation of Silicon (LOCOS) Isolation Process for Sub-Quarter Micron Design Rule
Authors: Jang Se-Aug , Kim Young-Bog , Byung-Jin Cho Byung-Jin Cho , Jong-Choul Kim Jong-Choul Kim
Published: October 2002

Double Spacer local oxidation of silicon (LOCOS) with shallow recess of silicon (DS-LOCOS) is described. The process has two spacers, a thin nitride spacer and a medium temperature chemical vapor deposition (CVD) oxide spacer. The process does not have intentional silicon recess etching step but achieves the shallow recess of silicon through nitride overetchings. It has been found that the key processes of the DS-LOCOS are both isolation etching and spacer etching, which critically affect 2ΔW and V
t roll-off behaviors of active transistor and junction characteristics. The DS-LOCOS achieves physical bird's beak length of below 0.03 µ m/side, field oxide volume ratio over 80%, and superior planar surface. The DS-LOCOS also gives no degradation in punchthrough voltage down to 0.20 µ m isolation spacing and in gate oxide reliability. These results show that the DS-LOCOS is a simple and promising isolation technology for sub-quarter micron design rule.
Application of a Junction Field Effect Transistor Structure to a Low Loss Diode
Authors: Yano Koji , Mitsui Masahito , Morita Jun-ichi , Kasuga Masanobu , Shimizu Azuma
Published: October 2002

A novel low loss diode with junction grids has been proposed. Numerical simulations reveal that, for this diode, designing a submicron grid width improves the tradeoff characteristics between the forward voltage drop and the leakage current, leading to characteristics superior to those of the Schottky barrier diode. The introduction of a lateral silicon-on-insulator (SOI) structure into the proposed diode is attractive for achieving such a small grid width. The simulation also demonstrates design methods for channel doping and thickness of the buried oxide layer in the SOI diode.
A Novel LDD-Structured Poly-Si Thin Film Transistors with High ON/OFF Ratio
Authors: Choi Kwon-Young , Hong-Seok Choi Hong-Seok Choi , Min-Koo Han Min-Koo Han
Published: October 2002

We have fabricated a new polycrystalline silicon thin film transistor (poly-Si TFT), entitled a gate-overlapped lightly doped drain (GO-LDD) TFT, which may reduce the leakage current without sacrificing the ON current. Both the source/drain and LDD region of GO-LDD TFT are formed simultaneously by employing the buffer oxide without any additional LDD doping. Experimental results show that the leakage current of the proposed TFTs is decreased by the magnitude of two orders without sacrificing the ON current. The low-temperature ion shower doping is also employed to fabricate both the source/drain and LDD in the GO-LDD TFTs without a troublesome ion implantation.
Self-Aligned Passivation Technology for Copper Interconnection Using Copper-Aluminum Alloy
Authors: Nobuyoshi Awaya Nobuyoshi Awaya , Toshio Kobayashi Toshio Kobayashi
Published: October 2002

A self-aligned passivation procedure for fabricating copper interconnection has been developed using Al–Cu alloy formation. With annealing at 350°C, very thin aluminum on the exposed copper wire reacts with copper to form Al–Cu intermetallic compound, whereas the underlying copper remains as a pure metal. Using the difference in the electrode potential between pure Al and the intermetallic compound, the unreacted aluminum on SiO2 can be selectively removed by acid treatment. Additional annealing at 350°C in the gaseous mixture of H2 and O2 creates a thin layer of aluminum oxide on the compound surface. This improves the resistance of the copper wire to oxidation. The passivated copper film is very stable at 250°C in air with only a small increase in resistivity (about 5%), while the sheet resistance of pure copper increases dramatically with time. The passivation also improves the adhesiveness of insulating film on the surface.
High-Rate GaAs Epitaxial Lift-Off Technique for Optoelectronic Integrated Circuits
Authors: Maeda Jun-ichi , Sasaki Yasushi , Dietz Nikolaus , Shibahara Kentaro , Yokoyama Shin , Miyazaki Seiichi , Hirose Masataka
Published: October 2002

In the epitaxial lift-off (ELO) technique, where a GaAs device structure is lifted off from a GaAs substrate using selective wet etching of an AlAs release layer, the etching rate of the AlAs layer is increased by a factor of ∼8 by raising the etchant temperature to 40° C and adding a surfactant and an antifoaming agent to the etching solution. The mechanism of the high-rate lift-off process is discussed based on the solubility and the diffusion coefficient of the etching product ( H2) in the etching solution. Photoluminescence measurement results show that the quality of the GaAs film is not degraded by the high-rate lift-off process. A high-rate lift-off technique for large-diameter wafers is proposed.
The Increase of the Native Oxide Thickness on H-Terminated Si Surfaces by Gaseous Contamination in a Clean Room Atmosphere
Authors: Itoga Toshihiko , Kojima Hisao , Jiro Yugami Jiro Yugami , Makoto Ohkura Makoto Ohkura
Published: October 2002

Gaseous impurities in a clean room (CR) atmosphere cause an increase in the native oxide thickness on H-terminated Si surfaces. The increase effect of ammonia is greater than other impurities. The increase mechanisms can be explained by a three-stage model. Ammonia generates an OH- group by reacting with H2O. The OH- group etches off H-terminated Si atoms and the effectiveness of the H-termination on reducing the native oxide growth is lost. As a result, the native oxide thickness increases. The native oxide growth can be suppressed by reducing the level of alkaline contamination in the CR atmosphere.
A Proposed Atomic-Layer-Deposition of Germanium on Si Surface
Authors: Sugahara Satoshi , Uchida Yasutaka , Kitamura Takuya , Nagai Tomonori , Matsuyama Motohiro , Hattori Takeo , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

A novel method has been proposed for monolayer deposition of Ge on the clean Si surface. The method is based on alternating and repeated exposures of the surface to germanium tetrachloride and atomic hydrogen. The former results in self-limiting adsorption of precursors on the Si surface, and the latter in extraction of surface-terminating Cl from the precursor-adsorbed Si surface. It has been confirmed experimentally that Ge can be deposited uniformly at one-monolayer thickness on the Si(100) surface using this metod.
Coulomb Blockade Effects in Edge Quantum Wire SOI MOSFETs
Authors: Ohata Akiko , Akira Toriumi Akira Toriumi , Ken Uchida Ken Uchida
Published: October 2002

Edge quantum wire MOSFETs were fabricated using the sidewall of an ultrathin SOI, and the electrical characteristics were investigated. In this device, current oscillations for gate voltage sweeping were clearly observed at 4.2 K. This effect is considered from the viewpoint of the Coulomb oscillations in the multijunction system on the edge quantum wire. Furthermore, we focus on two concerns regarding the application of the single electron tunneling (SET) devices. One concern is the phase instability of the Coulomb oscillations due to trapped or floating charges around the SET devices. To overcome this problem, we propose a double-gate edge SOI MOSFET. In fact, it is experimentally confirmed that the Coulomb oscillation phase is tunable. The other concern is the low driving capability of SET devices. To improve this, it has also been experimentally demonstrated that the direct transmission of SET signals to the conventional MOSFET current is possible. This means that the output impedance can be transformed locally or globally from high to low in the SET-device circuits hybridized with CMOS devices.
Step-Free Surface Grown on GaAs (111)B Substrate by Local Metalorganic Vapor Phase Epitaxy
Authors: Toshio Nishida Toshio Nishida , Naoki Kobayashi Naoki Kobayashi
Published: October 2002

In this paper we describe the realization of a step-free surface by local metalorganic vapor phase epitaxy (MOVPE) on (111)B GaAs surface. Surface stoichiometry is controlled by employing the surface photo-absorption method (SPA). High-temperature growth at 800° C on stable GaAs (111)B and a cooling procedure under the (2×2)-like surface conditions result in a step-free surface exceeding 10 µ m in diameter on the selectively grown GaAs mesa. Low two-dimensional nucleus density on the (111)B surface is demonstrated to illustrate the mechanism by which a wide step-free area is obtained, and step generation due to surface phase transition is also discussed.
Improvement of the Efficiency of Thermoelectric Energy Conversion by Utilizing Potential Barriers
Authors: Yoshimasa Nishio Yoshimasa Nishio , Tohru Hirano Tohru Hirano
Published: October 2002

A method of improving the efficiency of thermoelectric energy conversion by utilizing potential barriers is considered. Since potential barriers act as carrier energy filters, elimination of lower energy carriers results in an improvement of the efficiency of thermoelectric energy conversion (energy filtering method). The optimal height of potential barriers and the distance between the barriers is estimated within a semiclassical framework, i.e. using Boltzmann equation. Our calculated results show that this method works effectively for materials, in which acoustic phonon scattering is dominant compared with other scattering processes.
Missing-Dimer Structures and Their Kink Defects on Molecular Beam Epitaxially Grown ( 2×4) Reconstructed (001) InP and GaAs Surfaces Studied by Ultrahigh-Vacuum Scanning Tunneling Microscopy
Authors: Ishikawa Yasuhiko , Takashi Fukui Takashi Fukui , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

InP and GaAs(001)-(2×4) reconstructed surfaces prepared by molecular beam epitaxy (MBE) were studied by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) in combination with X-ray photoelectron spectroscopy (XPS). It was found that the missing dimers and their kink defects on InP have remarkably different properties from those of GaAs. Based on this finding, a new missing-dimer structure is proposed for InP (2×4) surfaces. As to the kink defects, no correlation was found on InP between the kink defect density and the Si doping level, although the XPS peaks clearly showed existence of Fermi level pinning. Thus, the model proposed recently by Pashley et al.. does not apply to the InP surface.
CdF2/CaF2 Resonant Tunneling Diode Fabricated on Si(111)
Authors: Izumi Akira , Matsubara Noriyuki , Kushida Yusuke , Tsutsui Kazuo , Sokolov Nikolai S.
Published: October 2002

We propose use of a new material, CdF2, and a heterostructure composed of CdF2 and CaF2 for applications of Si-based quantum effect devices. The optimum growth temperature for each layer of a CaF2/CdF2/CaF2 heterostructure grown by molecular beam epitaxy on a Si(111) substrate was determined. Resonant tunneling diodes consisting of this heterostructure on Si were fabricated and negative differential resistance whose P/V current ratio was 24 at maximum was detected at room temperature.
Room-Temperature Operation of a Lateral Tunneling Transistor Fabricated by Plane-Dependent Silicon Doping in Nonplanar Epitaxy
Authors: Ohnishi Hajime , Manabu Hirai Manabu Hirai , Kazuhisa Fujita Kazuhisa Fujita , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

Room-temperature operation of a lateral tunneling transistor fabricated by a plane-dependent Si-doping technique is demonstrated for the first time. In this technique the amphoteric nature of the Si dopant in GaAs growth by molecular beam epitaxy is utilized. Through use of this technique, a lateral p+- n+ interband tunneling junction was formed by the single growth of a heavily Si-doped GaAs layer on a GaAs(411)A patterned substrate and a quasi-planar process for device fabrication was made available. The transistor has gate-controlled negative differential resistance characteristics. By varying the gate voltage from -1.5 to 4.5 V, the peak drain current density and the peak-to-valley ratio are modulated from 161 to 251 mA/cm2 and from 3.1 to 4.4, respectively. These results indicate that this transistor successfully operates as a tunneling transistor.
Application of Semiconducting Low Temperature Grown GaAs to Improve Laser Diodes Grown on Si Substrates
Authors: Phua Cheng Chiang , Chong Tow Chong , Lau Wai Shing , Zhao Rong , Lu Dong , Chuen Hang Goo Chuen Hang Goo , Leng Seow Tan Leng Seow Tan
Published: October 2002

The application of a semiconducting low temperature grown GaAs (LT-GaAs) intermediate layer in laser diodes grown on Si by molecular beam epitaxy (MBE) reduces the threshold currents to half of that obtained in the sample without the semiconducting LT-GaAs intermediate layer. Furthermore, the emission spectra of the sample with the semiconducting LT-GaAs intermediate layer were predominantly single mode at and near the threshold currents, as compared to the multimode operation in the sample without the semiconducting LT-GaAs intermediate layer.