bluuebunny/crossref_metadata_2025 huggingface dataset:
Second-Order Piezoresistance Coefficients of p-Type Silicon
Authors: Matsuda Kazunori , Kanda Yozo , Yamamura Kazuhisa , Suzuki Katuhisa
Published: February 2005

Nonlinear piezoresistance effects in p-type Si resistors of three surface impurity concentrations were measured at room temperature. Stresses up to 174 MPa were applied along the <110 > and <111 > directions by bending a silicon cantilever. We determined all of the second-order piezoresistance tensor components, assuming that resistivity is more sensitive to shear than dilation, and that the hydrostatic pressure coefficient is zero.
Dependence of the Carrier Concentration Profile at the Si MBE Layer/p-Si Substrate Interface on the Si Substrate Preparation Method
Authors: Kanaya Hiroyuki , Shigekawa Hidemi , Hasegawa Fumio , Yamaka Eiso
Published: February 2005

The influence of the Si substrate preparation method on the carrier concentration profile at the Si MBE layer/p-Si substrate interface was studied. It was found that the Si substrate should be placed in the UHV MBE chamber immediately (within 10 minutes) after removal of the oxide layer to eliminate the p+ interface layer and must be heated up to 1250°C before MBE growth, in order to prevent carrier depletion at the interface and also to obtain good I-V characteristics of a diode with a Silicide/p-Si (or SiGe) MBE layer/p-Si substrate structure.
Mechanism of a Reduction of Dislocation Densities in Vertical-Gradient-Freeze-Grown GaAs Single Crystals
Authors: Okada Yasumasa , Sakuragi Shiro , Hashimoto Satoshi
Published: February 2005

In gallium arsenide single crystal grown by using a sealed ampoule procedure based on the vertical gradient freeze method, dislocation elimination with an increasing fraction of melt solidified was observed by chemical etching and X-ray topography. It is found that the dislocation density is as low as 103 cm-2 in the tail end of the 60-mm-long ingot. The mechanism of the reduction of dislocation densities is discussed in terms of the loop formation.
Degradation of Activation on Si-Implanted GaAs Crystal Wafers by Mechanical Surface Damages
Authors: Watanabe Masatoshi , Shinzawa Shoji , Okubo Seiichi , Otoki Yoohei , Kuma Shoji
Published: February 2005

Influences of mechanical damages of LEC grown GaAs wafer surfaces on activation have been investigated. In the results, the activation degrades with increase of the full width of half maximum value of X-ray rocking curve. Polished wafers have little change of the X-ray value and also of the activation.
Hydrogen Annealing of Transparent Gate MOS Diodes
Authors: Takato Hidetaka , Ishii Kenichi , Hayashi Yutaka
Published: February 2005

Transparent gate (indium tin oxide) MOS diodes were annealed in hydrogen ambient at temperatures ranging from 200 to 500°C. Decrease of interface state density and positive shifts of flat-band voltage were observed.
Bond-Valence-Sum Study on Possible Candidates for High-Tc Oxide Superconductors
Authors: Tanaka Shigenori , Fukushima Noburu , Niu Hiromi , Ando Ken
Published: February 2005

We have analyzed relationships between crystal structures and electronic states of layered transition-metal oxides in the light of bond valence sums. We introduce parameters representing excess charge and internal strain in the central MO2 planes (M=3d transition metal) and thereby characterize the electronic states of those oxides. Correlations between the superconducting transition temperature and those bond-valence-sum parameters are investigated for the high-T
c cuprate compounds and the possibility of making nonsuperconducting oxides superconducting is discussed.
Large Levitation Force due to Flux Pinning in YBaCuO Superconductors Fabricated by Melt-Powder-Melt-Growth Process
Authors: Murakami Masato , Oyama Terutugu , Fujimoto Hiroyuki , Taguchi Takahiro , Gotoh Satoshi , Shiohara Yuh , Koshizuka Naoki , Tanaka Shoji
Published: February 2005

An extremely large levitation force of as high as 30 N at a height of 1 mm was achieved in Ag-doped YBaCuO fabricated by the Melt-Powder-Melt-Growth process using a repulsive force against a 0.4 T rare-earth magnet at 77 K. The combination of a large J
c value and large shielding current loop is the source of such a large levitation force.
Critical Thickness for the Si1-xGex/Si Heterostructure
Authors: Fukuda Yukio , Kohama Yoshitaka , Ohmachi Yoshiro
Published: February 2005

An energy balance theory for predicting the critical thickness of the Si1-x
Ge
x
/Si heterostructure is derived based on an experimentally identified dislocation generation mechanism. The theory is in close agreement with experimental results. The critical thickness predicted by this theory is about four times that by the mechanical balance theory of Matthews and Blakeslee.
Enhancements in Current Density and Mechanical Properties of Y-Ba-Cu-O/Ag Composites
Authors: Lee Dominic , Salama Kamel
Published: February 2005

A liquid-phase processing method has been developed to manufacture bulk YBa2Cu3O
x
/Ag superconducting composites with large current carrying capacity and enhanced mechanical properties. Transport critical current density of 10,000 A/cm2 is obtained in nominal 15 wt.% Ag composite using continuous direct current at 77 K and zero applied field. Using a pulsed current of 2 ms duration, a critical current density of 22,000 A/cm2 is obtained. This composite has a Young's modulus of 100 GPa and a fracture stress of 70 MPa, which are substantially higher than those of sintered 1-2-3 superconductor.
Effect of Growth Temperature on Superconducting Phases of As-Grown BiSrCaCuO Thin Film Formed by RF Magnetron Sputtering
Authors: Kuroda Ken'ichi , Kojima Kazuyoshi , Yokoyama Kazuo , Hamanaka Koichi
Published: February 2005

The effect of growth temperature on superconducting phases has been studied for BiSrCaCuO thin films grown on MgO(100) substrates at temperatures in the range 500–660°C by RF magnetron sputtering from three targets. The chemical compositions of the metal elements of the films formed at each substrate temperature were adjusted to Bi:(Sr+Ca):Cu=2:3:2, 2:3.5:2.5 and 2:4:3. Low-T
c phases (232 phases), 232/243 phases and high-T
c phases (243 phases) were obtained above 580°C with the 2:3:2 composition, above 590°C with the 2:3.5:2.5 composition, and above 620°C with the 2:4:3 composition.
Effects of Magnetic Field and Temperature on the Critical Current Hysteresis in Tl-Ca-Ba-Cu-O Thin Films
Authors: Chang Hung-Lun , Juang Jenh-Yih , Liou Sy-Hwang , Uen Tzeng-Ming , Gou Yih-Shun
Published: February 2005

The behavior of the critical current density of Tl-Ca-Ba-Cu-O superconducting thin films in a cycling magnetic field was investigated. The hysteresis of the transport J
c manifested similar features to those found in polycrystalline Y-Ba-Cu-O and granular Nb, Al thin films in zero-field cooling. However, a novel result of the transport J
c in field-cooled samples has been observed. The results were attributed to the presence of a saturated trapped magnetic flux in the weaklink network. The effects of temperature on both the trapped flux and the transport J
c suggest the existence of various states of the trapped flux in the Tl-based superconducting thin films.
Stimulated Emission Near Ultraviolet at Room Temperature from a GaN Film Grown on Sapphire by MOVPE Using an AlN Buffer Layer
Authors: Amano Hiroshi , Asahi Tsunemori , Akasaki Isamu
Published: February 2005

We report the first observation of the room temperature stimulated emission near UV from a GaN film which was grown by metalorganic vapor phase epitaxy on a (0001) sapphire substrate using an AlN buffer layer. This indicates that the GaN film is promising for the realization of an UV laser diode.
Relaxation Oscillators Made of YBaCuO Thin Films
Authors: Kisu Takanobu , Enpuku Keiji , Yoshida Keiji , Takeo Masakatsu , Yamafuji Kaoru
Published: February 2005

It has been found that YBaCuO thin films exhibit hysteretic I-V characteristics in the case of high critical current densities of j
C(4.2 K)>106 A/cm2. By using the hysteretic I-V characteristics, relaxation oscillators can be constructed, where YBaCuO thin films are shunted by an external inductance and a resistance. The properties of the relaxation oscillator agree well with those of an equivalent circuit model. A preliminary experiment is also made on the optical response of the oscillation frequency in order to study the possibility of the relaxation oscillator as an optical sensor.
High Power Er3+-Doped Fiber Amplifier Pumped by 1.48 µm Laser Diodes
Authors: Suzuki Kazunori , Kimura Yasuo , Nakazawa Masataka
Published: February 2005

An output power of 51 mW at a wavelength of 1.552 µm is obtained for the first time from an InGaAsP laser diode pumped Er3+-doped fiber amplifier. The pump power is 107 mW and the amplifier efficiency reaches 48%. The Er3+ doping concentration is 630 ppm, and the fiber length is 20 m. The pump source is four InGaAsP laser diodes, which are operating at 1.45∼1.49 µm and are multiplexed using their polarizations and wavelengths. With simultaneous backward and forward pumping, the out put power is increased to 72 mW at a total pump power of 193 mW.
Structure and Luminescent Property of Y2O2S:Eu Thin Films Prepared by Magnetron Sputtering
Authors: Sowa Kunihiro , Tanabe Masami , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: February 2005

Y2O2S:Eu phosphor films were prepared by using a magnetron rf sputtering system from a Y2O2S:Eu target with excess sulfur. It has been found that the sulfur content in the films substantially influences the film structure, and that a phase transition from cubic Y2O3 to hexagonal Y2O2S is observed in the range from 1% to 2% additional sulfur content in the target. It has also been found that the film prepared under the condition of additional sulfur content shows a PL spectrum which is nearly the same as that of Y2O2S:Eu phosphor, whereas the film prepared by using a target without additional sulfur content shows nearly the same PL spectrum as Y2O3:Eu.
Photovoltaic, I-V and C-V Characteristics of SnO2/SiO2/a-Si:H/mc-Si:H Structures
Authors: Faraji Mohammad , Babras Suvarna , Mirzapour Safar , Agashe Chitra , Rajarshi Sharadchandra , Dusane Rajiv , Ghaisas Subhash
Published: February 2005

Structures of the type SnO2/SiO2/a-Si:H/mc-Si:H/Al and SnO2/SiO2/a-Si:H/mc-Si:H/a-Si:H/mc-Si:H/ were fabricated and studied for their I-V, C-V and photovoltaic characteristics. Results indicate that the structures behave like two diodes formed in the back-to-bak geometry. Furthermore, from the I-V studies under illumination, it is observed that a sufficient drift field exists in the structure without intentional doping of Si-based layers to yield a gain in current under illumination of about 104.
Effect of Core Structure on Spontaneous Polarization in New Ferroelectric Liquid Crystals with a Fluorinated Chiral Part
Authors: Shiratori Nobuyuki , Nishiyama Isa , Yoshizawa Atsushi , Hirai Toshihiro
Published: February 2005

We have designed a new chiral part, the 2-fluoro-2-methyl alkanoyloxy group and prepared new ferroelectric liquid crystals having this chiral part. The magnitude of spontaneous polarization of 4-(2-fluoro-2-methylhexanoyloxy)phenyl-4'-octyloxybiphenyl-4-carboxylate is about 7 times larger than that of a non fluorinated analogous compound. This remarkable increase of the P
s value should be attributable to a fluorine attached together with a methyl group directly to the chiral carbon. Moreover, the effect of the core structure on the spontaneous polarization is also discussed. Introduction of a pyrimidine ring in the core part greatly enhances the spontaneous polarization, over 400 nC/cm2.
High-Pressure Synthesis of Nd0.05(Ca0.3Sr0.7)0.95CuOy
Authors: Okai Bin
Published: February 2005

Substitution of alkaline-earth elements with other metallic elements was attempted in Ca1-x
Sr
x
CuO2. Of the fourteen elements examined (counting vacancy also as one), only Nd successfully replaced Ca and Sr to a small amount at x=0.7. Defect-type perovskite Nd0.05(Ca0.3Sr0.7)0.95CuO
y
was synthesized at 6 GPa and 920°C as a single phase. This material was semiconducting and did not show superconductivity.
Laser Cooling and Trapping of Argon and Krypton Using Diode Lasers
Authors: Katori Hidetoshi , Shimizu Fujio
Published: February 2005

The laser cooling and trapping of argon and krypton isotopes in the 1s5 metastable state are demonstrated using stabilized diode lasers. Even isotopes of krypton are separately trapped by tuning the laser frequency. For Ar and 84Kr, approximately 6×105 and 1×105 atoms are trapped, respectively.
Influence of the Surface Condition on the Thermal Relaxation of Strained SiGe Molecular Beam Epitaxy Layers
Authors: Kanaya Hiroyuki , Fujii Kunihiro , Cho Yukiko , Kumagai Yoshinao , Hasegawa Fumio , Yamaka Eiso
Published: February 2005

Dependence of the thermal stability of Si1-x
Ge
x
(x=0.23, 500 Å) layers on the surface conditions was studied. It was found that the samples with the surface oxide film or carbide were much stabler than as-grown MBE layers without any oxide or carbide for ∼800°C annealing. This result suggests that the thermal relaxation of the SiGe layers is greatly restrained by the surface oxide film or carbide, probably due to suppression of the introduction and/or propagation of dislocations by effects such as pinning at the surface.
Photostructural Change of Chalcogenide Glass Films by Irradiation of Laser Diode Emission
Authors: Chiba Kiyoshi
Published: February 2005

An optical change of As-Se-S-Ge amorphous chalcogenide film was observed by irradiation of a focused beam of laser diode emission of 830 nm wavelength. An optical analysis shows that this change occurs through energy band-tail absorption with an absorption coefficient of less than about 10 cm-1 and through a pure photon process.
Atmospheric Pressure Atomic Layer Epitaxy of ZnSe Using Zn and H2Se
Authors: Koukitu Akinori , Saegusa Akihiko , Kitho Masanori , Ikeda Hitoshi , Seki Hisashi
Published: February 2005

Atmospheric pressure ALE (atomic layer epitaxy) has been achieved to grow ZnSe for the first time using Zn and H2Se. It is confirmed that the growth rate is controlled by the self-limiting process itself. The ALE growth of ZnSe is observed in the substrate temperature range of 350–500°C and in the input partial pressure ranges of 5×10-6–1×10-4 atm for Zn and 4×10-5–2×10-3 atm for H2Se. Lattice parameters perpendicular to the surface plane and the values of FWHM for the diffraction pattern were obtained by the X-ray double-crystal diffraction measurement.
ESR and Nonresonant Microwave Absorption of ErBa2Cu3O7-δ and HoBa2Cu3O7-δ Single Crystals
Authors: Tagaya Kimihito , Fukuoka Nobuo , Nakanishi Shigemitsu
Published: February 2005

ESR measurements were performed for ErBa2Cu3O7-δ and HoBa2Cu3O7-δ single crystals from 77 K to room temperature. The ESR signals of Er2BaCuO5 and Ho2BaCuO5 were observed, and their temperature variations were investigated. A nonresonant microwave absorption was also observed below the superconducting critical temperature of 93 K, and was investigated. The principal values of lower critical field were determined.
Nitrogen-Doped ZnSe and ZnSSe Grown by Molecular Beam Epitaxy
Authors: Matsumura Nobuo , Tsubokura Mitsutaka , Nakamura Nobuhiro , Miyagawa Kazuhiro , Miyanagi Yoichi , Saraie Junji
Published: February 2005

Nitrogen-doped ZnSe and lattice-matched ZnSSe were grown on GaAs substrates by MBE using NH3 gas as a dopant source. The epilayers were characterized by photoluminescence. ZnSe was rather easily doped, and samples in which the acceptor-bound exciton line was a major line in the exciton emission region at 11 K were obtained. ZnSSe was less readily doped with nitrogen at the same NH3 effective pressure. However, the free-to-acceptor omission at 60 K was stronger in ZnSSe than in ZnSe, due to the effect of lattice matching.
Optical Symmetry of Ferroelectric Liquid Crystal Cells
Authors: Zhuang Zhiming , Clark Noel A. , Maclennan Joseph E.
Published: February 2005

We observe an exact optical symmetry in Surface Stabilized Ferroelectric Liquid Crystal (SSFLC) cells in polarized transmission optical microscopy and spectroscopy. A theoretical argument based on the intrinsic time reversibility of Maxwell's equations and energy conservation is developed to explain this symmetry. The results support the model of Clark and Rieker for zig-zag wall structure and illustrate the necessity of including the orientational binding of the director at the chevron interface.
Hot-Carrier-Immunity Degradation in Metal Oxide Semiconductor Field Effect Transistors Caused by Ion-Bombardment Processes
Authors: Kotani Koji , Shibata Tadashi , Ohmi Tadahiro
Published: February 2005

The degradation in MOS device characteristics as well as in their hot-electron injection immunity caused by ion-bombardment processes has been investigated. It has been found that neutral electron traps were generated due to the charging-up of the gate electrode during ion implantation. These neutral traps contribute to enhanced positive threshold shifts in the following hot-electron injection experiment. It has been demonstrated that such problems can be eliminated by grounding the gate electrode during ion implantation. Similar effects were also observed for a low-energy bias sputtering deposition process.
A Computer Simulation of the Recombination Process at Semiconductor Surfaces
Authors: Saitoh Toshiya , Hasegawa Hideki
Published: February 2005

A rigorous computer simulation of the recombination process through surface or interface states is made. It is shown that the surface recombination velocity is not a characteristic constant of the surface as is usually assumed, but depends strongly on the charge neutrality level of surface states, sign and amount of the fixed charge, the substrate doping level and profile, and the light intensity. It is also shown that S can be reduced by introducing a suitable amount of a fixed charge or by forming a highly doped surface layer. The effect of the device doping profile on S is also discussed.
Surface Impurities Encapsulated by Silicon Wafer Bonding
Authors: Abe Takao , Uchiyama Atsuo , Yoshizawa Katsuo , Nakazato Yasuaki , Miyawaki Mamoru , Ohmi Tadahiro
Published: February 2005

Wafer bonding techniques are shown to provide an important addition to methods used for the detection of residual impurities on the surfaces of polished and cleaned silicon wafers. Impurities were encapsulated in the interface made by wafer bonding, and analyzed by SIMS depth profiling. Significant concentrations of H, C, N, O, F and Cl were detected. The concentration of these elements did not change after two hour wafer bonding anneals in the range of 200°C to 800°C. For anneals at 1000°C and above both the diffusion of H and C from the bonded interface, and the aggregation of N and O were observed. It was confirmed by IR absorption and HR-TEM that oxygen in CZ crystals outdiffuses into the bonded interface and produces an SiO2 layer. Low-oxygen FZ wafers were used as a reference comparison. Elements such as F and Cl contained in the chemicals used to clean the wafers remained fixed at the bonded interface for the entire temperature range tested.
Photoluminescence of an InAlAs/InGaAs Quantum Well Structure Grown on a GaAs Substrate
Authors: Harmand Jean-Christophe , Matsuno Toshinobu , Inoue Kaoru
Published: February 2005

An In0.53Ga0.47As/In0.52Al0.48As quantum well structure was grown on a GaAs substrate by molecular beam epitaxy. A linearly graded InGaAlAs layer grown at 380°C was used as a buffer layer. The photoluminescence of this structure was observed at 15 K. The InGaAs quantum well thicknesses ranged from 20 Å to 500 Å. Emission of each quantum well was clearly resolved. The luminescence linewidths were analyzed and compared to the results reported for the material system grown lattice-matched to InP. We deduced an enhancement of the alloy clustering and well thickness fluctuations which probably do not exceed 1 monolayer but which have a large lateral extension. These features are related to the lattice mismatch of the structure with the substrate.
Chemical Bonding Features of Fluorine and Boron in BF2
+-Ion-Implanted Si
Authors: Kinoshita Tsuyoshi , Takakura Masaru , Miyazaki Seiichi , Yokoyama Shin , Koyanagi Mitsumasa , Hirose Masataka
Published: February 2005

The chemical bonding configurations of fluorine and boron atoms in a BF2
+-ion-implanted Si network have been studied by using X-ray photoelectron spectroscopy, infrared absorption and Raman scattering measurements. It is concluded that fluorine atoms in as-implanted Si are mainly incorporated as BF bonds. By annealing at 900°C, the BF bonds are thermally decomposed to form four fold-coordinated acceptors as well as thermodynamically stable SiF
x
bonds (x=2, 3) in the matrix.
Source-Drain Metal Contact Effects in Short-Channel a-Si:H Thin-Film Transistors
Authors: Fortunato Guglielmo , Gentili Massimo , Luciani Laura , Mariucci Luigi , Pecora Alessandro , Petrocco Giovanni
Published: February 2005

Short-channel hydrogenated amorphous silicon thin-film transistors have been fabricated by using electron-beam lithography with the shortest channel length of L=0.2 µm. As source-drain contacts, Cr or Al have been used. In the case of Cr-contact field-effect mobility, µFE, degradation for decreasing L has been observed, while the devices with Al-contacts show µFE around 0.7 cm2/V ·s independently of the channel length. This result is related to low parasitic resistance shown by our devices and attributed to the Al-diffusion in the source-drain contact regions. The calculated maximum operating frequency for the shortest channel devices is about 250 MHz.
Pd-Gate a-Si:H Thin-Film Transistors as Hydrogen Sensors
Authors: Mariucci Luigi , Pecora Alessandro , Puglia Carla , Reita Carlo , Petrocco Giovanni , Fortunato Guglielmo
Published: February 2005

Top-gate a-Si:H thin fihn transistors (TFTs), with Pd as a gate electrode and silicon nitride as a gate insulator, have been fabricated and successfully operated as hydrogen sensors. The sensitivity mechanism of such devices resides in the catalytic behavior of Pd towards H2-molecules and in the formation of a H-dipole at the Pd/gate insulator interface, which influences the threshold voltage of the transistor. The measured H-response is similar to that relative to a c-Si Pd-gate MOSFET. The obtained results show possible promising applications of the use of a-Si:H TFTs in the field of chemical sensors.
Improvement of GaAs Metal-Semiconductor Field-Effect Transistors Characteristics on SiO2 Back-Coated Si Substrate by Metalorganic Chemical Vapor Deposition
Authors: Egawa Takashi , Nozaki Shinji , Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: February 2005

We have shown that the use of SiO2 back-coated Si substrate is effective in obtaining a low background electron concentration in an undoped GaAs layer grown on Si, particularly at high temperature, by MOCVD. Higher growth temperature improves the crystallinity of the GaAs layer grown on Si and helps to suppress the sidegating effect of GaAs MESFET's fabricated on Si. A low background electron concentration in the undoped GaAs layer is required for good pinch-off of the MESFET's. By using SiO2 back-coated Si substrate, the undoped GaAs with an electron concentration of as low as 1×1015 cm-3 could be grown even at 750°C. The maximum transconductance of 160 mS/mm, good pinch-off and suppressed sidegating were achieved for the 2.5 µm gate length MESFET on SiO2 back-coated Si.
Phase-Locked Two-Dimensional Arrays of Vertical Cavity Surface Emitting Lasers
Authors: Yoo Hoi-Jun , Hayes J. R. , Paek E. G. , Harbison J. P. , Florez L. T. , Kwon Young-Se
Published: February 2005

We report the characteristics of two-dimensional phase-locked arrays of vertical cavity surface emitting lasers. Three different two-dimensional array structures have been realized, they are a 2×3 periodic array of 10 µm squares, a hexagonal array and a centered hexagonal array of 5 µm hexagons. All arrays were fabricated using the same technique which was a combination of mesa etching and oxygen implantation isolation. The threshold current of 2×3 periodic array was 24 mA, hexagonal array was 30 mA and centered hexagonal array was 22 mA. The far field beam angle was about 2°. The centered hexagonal array has the most circularly symmetric far field beam pattern.
On The Barrier Height of Schottky Diodes of Au on n-GaSb
Authors: Murawala Prakash A. , Arora Brij Mohan
Published: February 2005

Schottky barrier diodes of Au on n-type liquid phase epitaxially grown GaSb with an ideality factor of close to unity (n=1.1) have been fabricated by optimising the surface preparation condition before forming the metal contact on GaSb. Electrical properties of these Schottky barriers have been investigated by I-V and C-V measurements over a range of temperature from 180 K to 370 K. Barrier height of near-ideal Schottky barrier diodes is 0.47 eV and follows the “2/3E
g rule”. These results are important in the current debate on the formation of Schottky barriers in III–V compound semiconductors.
Possibility of Magnetic Ordered States in Semiconductor Quantum Dot System
Authors: Sugimura Akira
Published: February 2005

The possibility of magnetic ordered states in a semiconductor quantum dot array is proposed theoretically. On the basis of the calculated on-site repulsion energy and the electron transfer energy, it is found that the GaAs/AlGaAs quantum dot system can be described by the one-band Hubbard model. Within the framework of the mean field approximation for this model, it is shown that the magnetic ordering such as ferro- and antiferromagnetism can be expected in quantum dot arrays with a dot width and spacing of 50 Å ∼200 Å.
High Performance Laser Amplifiers at 1.5 µm using E-Gum Evaporated Hafnium Di-Oxide Coatings
Authors: Tiemeijer L. F. , Kuindersma P. I. , Krekels H. C. J. , Es-Spiekman W. v. , Hendrix L. J. M. , Ludwig R. , Küller L.
Published: February 2005

E-gun evaporated Hafnium di-Oxide anti-reflective coatings are shown to be an attractive alternative for sputtered Silicon Oxide AR coatings. Laser amplifiers were fabricated using this material and a modal reflectivity as low as 1.7×10-4 was obtained. A single pass gain of 26 dB together with a ripple as low as 2 dB for the TE mode were measured. Furthermore a 3 dB output saturation power of +8 dBm and a fiber coupling loss of 3.5 dB/facet were measured.
Preparation of Y-Ba-Cu-O Superconductors with High Critical Current Density by Unidirectional Melt Solidification
Authors: Kase Jun-ichiro , Shimoyama Jun-ichi , Yanagisawa Eiji , Kondoh Shinji , Matsubara Toshiya , Morimoto Takeshi , Suzuki Mitsuru
Published: February 2005

Y-Ba-Cu-O superconductors with high J
c have been prepared by a unidirectional melt solidification method. Uniformly oriented plate-shaped YBa2Cu3O7-y
crystals containing small particles of Y2BaCuO5 have been grown successfully using the material with the nominal composition of Y1+x
Ba2-x
Cu3-2x
O
z
(x≦0.4) as a starting material. The J
c values of the unidirectionally solidified Y-Ba-Cu-O samples, measured at 77 K using a four-probe method with continuous direct current, were 4600 and 12000 A/cm2 in 1 and 0.25 T, respectively. These values nearly coincided with those estimated from magnetization hysteresis loops using Bean's critical state model.
Superconducting and Structural Properties of EuBa2Cu3O7-δ Ultrathin Films Deposited on MgO(100) Substrates Using Magnetron Sputtering
Authors: Michikami Osamu , Asahi Masayoshi , Asano Hidefumi
Published: February 2005

EuBa2Cu3O7-δ thin films were produced on MgO(100) substrates at 580°C using planar-type magnetron sputtering and were studied by X-ray diffraction and RHEED. The c-oriented films were epitaxially grown with a crystal orientation of [110]EuBaCuO//[010]MgO. Films more than 1000 Å thick exhibited T
c endpoints of ∼90 K. As film thickness decreased, superconducting properties deteriorated. However, even films with 2-unit-cell thickness became superconducting. The cause of the deterioration of superconducting properties in ultrathin films is discussed on the basis of the relationship between lattice matching and structural properties.
Experimental Studies on Phase Transitions in an Antiferroelectric Liquid Crystal
Authors: Orihara Hiroshi , Fujikawa Tetsuya , Ishibashi Yoshihiro , Yamada Yuichiro , Yamamoto Norio , Mori Kahoru , Nakamura Koji , Suzuki Yoshiichi , Hagiwara Takashi , Kawamura Ichiro
Published: February 2005

The effect of optical purity on the antiferroelectric phase transition and the field-induced ferroelectric phase transition in Sm CA
* were studied by means of dielectric measurements and observations of D-E hysteresis loops. The Curie-Weiss law was found to hold in Sm A and the Curie-Weiss constant to increase as the optical purity is reduced. Three types of D-E curves were obtained in the Sm CA
* phase. It was found that a double hysteresis loop changed into a single one at high frequencies. The results obtained are discussed on the basis of a phenomenological theory.
Low-Temperature Growth of Polycrystalline AlN Films by Microwave Plasma CVD
Authors: Someno Yoshihiro , Sasaki Makoto , Hirai Toshio
Published: February 2005

The growth of polycrystalline AlN film at a rate of 60 nm·min-1 was accomplished at a substrate temperature of 550°C by a coaxial-line-type microwave plasma chemical vapor deposition (CVD) method using the AlBr3-H2-N2 gas system. Excellent c-axis orientation was observed on the film having a half-width rocking curve of (001)AlN (Δθ50) of 2.1 degrees. No carbon or bromine was detected by the AES measurements.
Observation of the Surface and Structure of Very Thin Ti Film
Authors: Iida Shoji
Published: February 2005

Ti was deposited onto pyrex glass at room temperature under high vacuum pressure such as 5×10-10 torr; then film structures were observed with TEM and AES. It was found that at the early stage of deposition, the main component of the thin layer, whose thickness was up to about 80 Å, was TiO. However, in the thicker layer, the amount of TiO decreased, and the main component became Ti. Deposited Ti film formed an island state whose thickness was up to about 70 Å, and micro-crystallization began when the film reached about 400 Å at room temperature.
Estimation of the Density and Roughness of Thin Monolayer Films by Soft X-Ray Reflectivity Measurements
Authors: Kikuchi Yukiko , Itoh Masamitsu , Mori Ichiro , Takigawa Tadahiro
Published: February 2005

Thin monolayer films of molybdenum and carbon were deposited by an electron beam evaporation system equipped with an in situ soft X-ray reflectivity monitoring instrument. The densities of the films were estimated from reflectivity measurements during deposition. The densities of the films were about 20% below the bulk value. It was proved that this film density decrease cannot be ignored in estimating the surface roughness by optical measurements. The rms roughness estimated from reflectivity measurements of the monolayer films by correcting the density was in good agreement with the STM results.
Electro- and Photoreflectance of Ultrathin Ge/Si Superlattices Grown by Phase-Locked Epitaxy
Authors: Asami Kumiko , Miki Kazushi , Sakamoto Kunihiro , Sakamoto Tsunenori , Gonda Shun-ichi
Published: February 2005

Optical studies of ultrathin Ge/Si superlattices grown on (001) Si substrates by phase-locked epitaxy have been carried out. The structures consist of alternating layers of pure Ge and Si with periods of 8, 10 and 12 monolayers. Using photo- and electroreflectance (PR and ER), four structurally induced optical transitions have been observed in the energy ragion 0.76–2.5 eV in both systems with periods of 8 and 10 monolayers. The transition energies show a blue shift with decreasing strain. At a growth temperature of 400°C, the PR and ER spectra of Ge6/Si6, which has a period of 12 monolayers, show not alloylike behavior but superlattice features similar to the samples with periods of 8 and 10 monolayers.
Characterization of µc-Si:H Films Prepared by H2 Sputtering
Authors: Tonouchi Masayoshi , Moriyama Fuminori , Miyasato Tatsuro
Published: February 2005

Hydrogenated microcrystalline Si films were prepared on fused quartz and Si substrates by H2 sputtering of a Si target. The grain size increases with the increasing electrical power required for the sputtering, P
s, where the smallest grain size is estimated to be 1.1 nm of the Si and 7.1 nm on the quartz. It is also discovered that Raman spectra change with P
s but in a different manner on the Si and the quartz substrates. A reason for this difference is discussed.
High Breakdown P-Channel InSb MOSFET
Authors: Tu S. L. , Lan W. H. , Chiou T. S. , Yang S. J. , Huang K. F.
Published: February 2005

P-channel InSb MOSFET is fabricated by anodic oxidation and SiO evaporation for the MOS gate structure and by Cd diffusion for the source and drain. A breakdown voltage exceeding 11 V is obtained in the drain junction, which renders the drain current saturation fully observable. An on-off ratio of 104 in the drain current is also obtained, indicating that the present InSb MOSFET is useful for a good switching operation.
Preparation of Superconducting Bi-Sr-Ca-Cu-O Films with Preferred Orientation through a Metal Alkoxide Route
Authors: Hirano Shin-ichi , Hayashi Takashi , Tomonaga Hiroyuki
Published: February 2005

Superconducting Bi-Sr-Ca-Cu-O films were prepared through a metal alkoxide route. The superconducting thin films composed of high T
c and low T
c phases with (00l) preferred orientation were successfully prepared at 850°C for 30 min on MgO(100) single-crystal substrates by a dip-coating method using partially hydrolyzed metal alkoxide solutions with 2-dimethylaminoethanol. The high T
c Bi2Sr2Ca2Cu3O
x
phase was found to form from the Bi2Sr2CuO
x
phase through the low T
c Bi2Sr2CaCu2O
x
phase in the Bi-Sr-Ca-Cu-O system. The preferentially orientated thin films prepared at 850°C exhibited the superconducting transition with an onset of 114 K and an offset of 65 K.
Crystal Structure and Superconducting Properties of BaPb1-x-yBixCuyO3-δ
Authors: Kinoshita Kyoichi , Shibata Hiroyuki , Yamada Tomoaki
Published: February 2005

The crystal structure and superconducting properties of the BaPb1-x-y
Bi
x
Cu
y
O3-δ system are investigated. It is shown that the orthorhombic perovskite-type structure is retained up to a Cu concentration y of about 0.35. The system shows bulk superconductivity for a wide range of Cu concentrations, and the maximum T
c is about 13 K, which is almost the same as that of the BaPb1-x
Bi
x
O3 system. The origin of superconductivity is discussed in relation to the BaPb1-x
Bi
x
O3 system.
Crystal Structure of Low Oxygen-Defect Tetragonal Ba2YCu3O6.75
Authors: Shibata Hiroyuki , Kinoshita Kyoichi , Yamada Tomoaki
Published: February 2005

The crystal structure of the low oxygen-defect tetragonal Ba2YCu3O6.75 (tetra-I) phase synthesized under high oxygen pressure is determined by Rietveld analysis of X-ray powder diffraction. The phase is similar to the conventional nonsuperconducting tetragonal phase (tetra-II) and oxygen atoms randomly occupy in Cu-O chain sites, where oxygen defect concentration is lower than in the tetra-II phase. Precise differences between the tetra-I phase and other phases of Ba2YCu3O7-δ are discussed.
Tetragonal-Orthorhombic Structural Phase Transition in the (Gd2/3Ce1/3)4[La1/3(Ba1-xLax)2/3]4Cu6Oz System
Authors: Ichinose Ataru , Wada Takahiro , Yaegashi Yuji , Yamauchi Hisao , Tanaka Shoji
Published: February 2005

We have synthesized (Gd2/3Ce1/3)4[La1/3(Ba1-x
La
x
)2/3]4Cu6O
z
with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The crystal system of the samples with x=0.2–0.4 was found to be orthorhombic, while that of the samples with x=0, 0.1 and 0.5 was tetragonal. The samples with x=0 and 0.1 exhibited superconductivity with T
c
on=30 K and 25 K, respectively, while those with x=0.2–0.5 were nonsuperconducting. The oxygen content of each sample was analyzed to determine the average copper valence.
Magnetic Properties of 40 K Class Oxide Superconductor (Gd, Ce)4(La, Ba, Sr)4Cu6O18.8
Authors: Wada Takahiro , Kaneko Tetsuyuki , Ichinose Ataru , Yaegashi Yuji , Ikegawa Sumio , Yamauchi Hisao , Tanaka Shoji
Published: February 2005

The superconducting properties of a 40 K class superconductor, (Gd0.667Ce0.333)4(La0.334Ba0.333Sr0.333)4Cu6O18.8, were investigated by transport and magnetization measurements. The lower critical field, H
c1(0), estimated from the field dependence of magnetization was 110 Oe. Adopting the 80% points of the resistive superconducting transition as T
c's in magnetic fields, the upper critical field, H
c2(0), was determined to be 72.7 T. The superconducting material parameters were derived using these values for H
c1(0) and H
c2(0): κGL=126, ξGL(0)=21 Å, λGL(0)=2680 Å and H
c(0)=4.1 kOe.
Preparation of Pb-Doped Bi-Sr-Ca-Cu-O Superconductors by a Hot-Press Method
Authors: Ikeda Hiroshi , Yoshizaki Ryozo , Yoshikawa Kozo , Tomita Nobuyoshi
Published: February 2005

Synthetic conditions of Pb-doped Bi-Sr-Ca-Cu-O oxide superconductors produced by a technique of a uniaxial hot-press method were studied. The quality of the samples was measured by means of X-ray diffraction analysis, secondary electron microscope measurement and density measurement. The hot-pressed sample showed a single 2223-phase with density close to the ideal value.
Nonbolometric Infrared Detection in La2-xSrxCuO4 and YBa2Cu3Oy Epitaxial Thin Films
Authors: Tanabe Keiichi , Enomoto Youichi , Suzuki Minoru , Iwata Tsunekazu , Yamaji Akihiko
Published: February 2005

The electrical responses to infrared radiation of La2-x
Sr
x
CuO4(100) and YBa2Cu3O
y
(110) epitaxial thin films with relatively low T
c values and J
c values of 104–105 A/cm2 are studied using modulated laser light. These films show apparent nonbolometric responses at temperatures below the transition regions which are strongly dependent on the bias current. The difference in the observed responsivity between these high-T
c materials and BaPb1-x
Bi
x
O3 can be explained on the basis of nonequilibrium superconductivity.
Structure, and Electrical and Magnetic Properties of Nonsuperconducting BiVS3 and BiNbS3
Authors: Matsuura Kiyotaka , Wada Takahiro , Suzuki Nobuo , Nakamizo Takashi , Ikegawa Sumio , Yamauchi Hisao , Tanaka Shoji
Published: February 2005

We have prepared ternary chalcogenides, BiMS3 with M=Nb and V, and grown their single crystals. BiVS3 did not show superconductivity, but exhibited metallic behavior in its electrical conduction in the temperature range of 1.6 K to 300 K. We found that BiVS3 had a charge density wave (CDW) transition around 160 K. The electrical conductivity of BiNbS3 was metallic in the same temperature range. The Hall coefficient, R
H, of BiNbS3 was positive in the temperature range between 4.2 K and 300 K. The density of holes calculated from the measured value of R
H, assuming an electrical conduction by holes only, was around 4×1021 cm-3.
Crystalline Transformations in Amorphous Fe73.5Cu1Nb3Si16.5B6 Alloy
Authors: Fujinami Masanori , Hashiguchi Yoshihiro , Yamamoto Tsuyoshi
Published: February 2005

The crystallization behavior of the amorphous Fe73.5Cu1Nb3Si16.5B6 alloy has been investigated by Mössbauer spectroscopy and X-ray diffractometry. Fine crystalline grains of about 10 nm diameter are produced uniformly by annealing at 550°C for 1 hour in nitrogen atmosphere. The predominant crystalline phase is assigned to the Fe-Si alloy with DO3 structure and neither intermetallic compounds nor an amorphous phase can be recognized in the Mössbauer spectrum. The addition of 1 at% Cu to amorphous Fe-Si-B merely brings about a lowering of the crystallization temperature, while that of 3 at% Nb leads to a rise in the crystallization temperature and simultaneous formation of Fe-Si alloy and Fe3(Si, B). Their effects simultaneously influence the crystallization behavior in the amorphous Fe73.5Cu1Nb3Si16.5B6 alloy, and lead to the production of Fe-Si alloy with uniform ultrafine grains. Annealing at 720°C for 1 hour gives rise to the growth of the fine grains and the formation of Fe3(Si, B).
Sequential Lattice Relaxation Model within the Double Configuration Coordinate for the DX Center in AlGaAs
Authors: Mochizuki Yasunori , Mizuta Masashi , Oshiyama Atsushi
Published: February 2005

We propose a new model for the D
X center in Al
x
Ga1-x
As, for which symmetry-conserving lattice relaxation (breathing distortion) is followed by successive symmetry-lowering lattice relaxation (Jahn-Teller distortion) induced by electron capture at a triplet resonant state in the conduction band. The degeneracy of the triplet state is lifted upon electron capture, and consequently a singlet state within the forbridden gap (the D
X center) as well as a resonant doublet state appears. We argue that the photoionization of the D
X center is an intracenter optical transition between the singlet and doublet states, and that thermal emission and capture of electrons occur through the resonant triplet state. The sequential lattice relaxation model proposed here provides a natural explantation for the puzzling experimental data available up to now.
Heavily Carbon-Doped P-Type InGaAs Grown by Metalorganic Molecular Beam Epitaxy
Authors: Akatsuka Takeshi , Miyake Ryuji , Nozaki Shinji , Yamada Takumi , Konagai Makoto , Takahashi Kiyoshi
Published: February 2005

In order to overcome a problem of the lattice mismatch between heavily carbon-doped p-GaAs and moderately doped GaAs, we have grown heavily carbon-doped InGaAs with a hole concentration of 2.6×1020 cm-3 and resistivity of 6.5×10-4 Ω·cm by MOMBE, in which the indium content was adjusted so that its lattice constant became equal to that of SI GaAs. In the lattice-matched InGaAs, the indium molar fraction determined from the Raman spectrum and the bandgap from the 4.2 K photoluminescence spectrum are 0.05 and 1.396 eV, respectively.
Contact Failures due to Polymer Films Formed during Via-Hole Etching
Authors: Mayumi Shuichi , Nishida Shuichi , Ueda Seiji
Published: February 2005

The contact resistance between the first metal and the second metal for double-level metallization was increased due to the polymer film formed during via-hole etching with C2F6/CHF3 plasma. The resistance increases with increasing over-etching time and etching pressure, or with decreasing electrode temperature for the via-hole etching. A Si-coated electrode is more effective in reducing the contact resistance than a carbon electrode is. Furnace heating at 380°C as a post-treatment is very effective in removing the etching polymer and in decreasing the contact resistance.
Rietveld Refinement of the Structure of TlSr2CaCu2O7 by X-Ray Powder Diffraction Data
Authors: Doi Toshiya , Usami Katsuhisa , Kamo Tomoichi
Published: February 2005

Single phase TlSr2CaCu2O7 was synthesized, and the crystal structure was refined from X-ray powder diffraction data using Rietveld analysis. The structure has single Tl-O sheets and tetragonal symmetry (a=3.7859 Å, c=12.104 Å) with space group P4/mmm, and is similar to TlBa2CaCu2O7 and Tl0.5Pb0.5Sr2CaCu2O7 (1212 type). Possible substitution of about 14% of Ca-sites with Tl ions was suggested.
Preparation of High-Tc Y-Ba-Cu-O Films by Three-Target Magnetron Sputtering
Authors: Akutsu Nakao , Fukutomi Masao , Katoh Kazuhiko , Takahara Hidefusa , Tanaka Yoshiaki , Asano Toshihisa , Maeda Hiroshi
Published: February 2005

The mechanism of deviation in the composition of sputtered films from the target was studied using a three-target magnetron sputtering system. Films were prepared in two different deposition geometries: first, the three targets were facing the substrate, and second, they were turned far away from the substrate. A significant difference was observed in the gas pressure dependence of film composition between these two geometries. The difference was attributed to the difference in bombardment probability of the films by high-energy O2- ions. The T
c of the film deposited with no ion bombardment effect was 84 K.
Fabrication of Y-Ba-Cu-O Superconductor/La-Ca-Mn-O Oxide Magnetic Material Layered Films
Authors: Ohno Toshiyuki , Kasai Masahiro , Kanke Yoko , Kozono Yuuzoo , Hanazono Masanobu , Sugita Yutaka
Published: February 2005

To investigate the interaction between a superconductor and magnetic material, fabrication of oxide superconductor/oxide magnetic material layered films was examined. From the secondary ion mass spectroscopic analysis, it was found that YBa2Cu3O
y
can be fabricated on antiferromagnetic La0.3Ca0.7MnO3, and there is little reaction at the interface of these two layers. However, Bi2Sr2CaCu2O
y
could not be fabricated because of mutual diffusion at the interface of Bi2Sr2CaCu2O
y
and La0.3Ca0.7MnO3.
Enhancement of Second-Harmonic Generation in Langmuir-Blodgett Monolayer Films by Molecular Mixing of Homologous Amphiphiles
Authors: Nakamura Ken-ichi , Era Masanao , Tsutsui Tetsuo , Saito Shogo
Published: February 2005

Two homologous azobenzene-linked amphiphiles, which possess the same chemical structure except for hydrophilic groups, were mixed at the molecular level in a monolayer. The polar amphiphile with nitro substituent as a hydrophilic group was vertically oriented in the mixed monolayer by performing molecular mixing with the homologous amphiphile with small polarity. Strong second-harmonic generation compared with those in each single-component monolayer was observed in the mixed monolayer.
Bi-Pb-Sr-Ca-Cu-O Superconducting Fibers Drawn from Melt-Quenched Glass Preforms
Authors: Onishi Masashi , Kohgo Takashi , Chigusa Yoshiki , Watanabe Kazuo , Kyoto Michihisa , Watanabe Minoru
Published: February 2005

Bi-Pb-Sr-Ca-Cu-O glass fibers were drawn from melt-quenched glass preforms by the method that is ordinarily applied to optical fiber fabrication. The drawn fibers were very flexible, and their surfaces were smooth. The glass fibers were crystallized by annealing and had superconducting properties. The annealed (1133 K, 240 hour) Bi1.6Pb0.4Sr2Ca2Cu3O
x
fiber exhibited superconductivity with a T
c(zero) of 68 K and a critical current density (30 K, zero magnetic field) of 22 A/cm2.
Material Quality in GaAs-on-Si Grown by Metalorganic Molecular Beam Epitaxy
Authors: Uneta Makoto , Watanabe Yoshio , Ohmachi Yoshiro
Published: February 2005

GaAs layers are epitaxially grown on Si substrates by metalorganic molecular beam epitaxy. The crystalline quality of GaAs-on-Si largely depends on the As4 flux in addition to the growth temperature. Optimization of As4 flux also improves the surface morphology of GaAs. These can be attributed to higher surface mobility of Ga-containing species under a low As-overpressure condition.
A Simple Method of Fabricating Preferentially Oriented YBa2Cu3O7-x Film on Silver Substrates
Authors: Suzuki Mitsuru , Kondoh Shinji , Yanagisawa Eiji , Shimoyama Jun-ichi , Irisawa Naoshi , Morimoto Takeshi
Published: February 2005

Porous YBa2Cu3O7-x
film stuck to a flexible silver substrate was easily fabricated by sintering a doctor-blade-cast green sheet of YBa2Cu3O7-x
placed on the silver substrate. Furthermore, preferentially oriented dense YBa2Cu3O7-x
film was also fabricated by adopting a copper plated silver substrate and then sintered below the melting temperature of silver. A possible mechanism for the appearance of the preferentially oriented dense YBa2Cu3O7-x
is discussed based on the liquid-phase sintering in the YBa2Cu3O7-x
-CuO-Ag system.