bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed Laser Deposition of Ferroelectric (Na0.5K0.5)NbO3-Based Thin Films
Authors: Saito Takehisa , Adachi Harumi , Wada Takahiro
Published: July 2005

Ferroelectric (Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 thin films were epitaxially grown on a (100)SrRuO3∥(100)SrTiO3 substrate by pulsed laser deposition. Crystallographic analysis of the film was performed using conventional X-ray diffraction analysis and rocking curve measurements. High resolution X-ray diffraction reciprocal space map was also measured to analyze the crystallographic relationship between the grown film and the SrTiO3 substrate and to determine the strain state of the film. The full width at half maximum of the rocking curve was as small as 0.19° and the determined pseudo-tetragonal lattice parameters were a=3.947 Å and c=3.955 Å. The P–E hysteresis loop of the film was characteristic of ferroelectric behavior.
Design Technique for Ramped Gate Soft-Programming in Over-Erased NOR Type Flash EEPROM Cells
Authors: Baek Chang-Ki , Kim Bomsoo , Quan Wu-yun , Kwon Wookhyun , Park Young June , Min Hong Shick
Published: July 2005

We present an efficient design technique for implementing the optimal ramped gate soft-programming for curing the over-erased flash EEPROM cells. The technique does not rely on any I–V model but is solely based upon using the actual cell performance data and enables accurate prediction of programming time, given supply current (I
S). The full utilization of available supply current renders the programming speed much faster and also enables reliable multi-bit soft-programming. The ramped gate scheme induces a strong self-convergence of the simultaneously up-shifted threshold voltages regardless of their initial values or the variations of the shift speed from cell to cell.
Optimization of Annealing Process of Pulsed RF Decoupled Plasma Nitridation Oxynitrides
Authors: Lim Sang Woo , Tekleab Daniel , Luo Tien-Ying , Grudowski Paul
Published: July 2005

Optimization of post nitridation annealing (PNA) in plasma nitrided gate oxide integration exhibited reduction of gate leakage current and improvement of negative bias temperature instability (NBTI) without drive current loss have been demonstrated. An improved interface quality by a high temperature or a high pressure O2 PNA is the main factor to improve channel mobility. The addition of both post clean annealing (PCA) and post oxidation annealing (POA) allows for gate dielectric scaling down with the benefit of drive current improvement. An increase in oxide thickness and a decrease in relative nitrogen concentration resulted in the improvement of NBTI characteristics.
Dependence of Giant Tunnel Magnetoresistance of Sputtered CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and Annealing Temperature
Authors: Hayakawa Jun , Ikeda Shoji , Matsukura Fumihiro , Takahashi Hiromasa , Ohno Hideo
Published: July 2005

We investigated the dependence of giant tunnel magnetoresistance (TMR) on the thickness of an MgO barrier and on the annealing temperature of sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si wafers. The resistance-area product exponentially increases with MgO thickness, indicating that the quality of MgO barriers is high in the investigated thickness range of 1.15–2.4 nm. High-resolution transmission electron microscope images show that annealing at 375°C results in the formation of crystalline CoFeB/MgO/CoFeB structures, even though CoFeB electrodes are amorphous in the as-sputtered state. The TMR ratio increases with annealing temperature and is as high as 260% at room temperature and 403% at 5 K.
Chirp Parameter of Electroabsorption Modulators with InGaAsP Intrastep Quantum Wells
Authors: Shin Dong-Soo , Jeong Heejun
Published: July 2005

The chirp parameter of electroabsorption modulators (EAMs) with intrastep quantum wells (IQWs) based on the InGaAsP material system is investigated theoretically. The chirp parameter of the IQW EAM, calculated by using the Kramers-Kronig relation, shows a discontinuity at a low voltage due to the blue shift in transition energy. Once the red shift is initiated, the chirp of the IQW EAM is similar to that of the conventional quantum-well (QW) EAM. Comparison with the conventional QW EAM shows that the IQW EAM could still be operated under high optical power without the compromise in chirp and absorption loss.
Electric Spark Ignition Eneries of Coating Polymer Powders
Authors: Choi Kwang Seok , Yamaguma Mizuki , Shin Dae Sung , Joung Jae Hee
Published: July 2005

In this paper, we report on experimental results dealing with the minimum ignition energy (MIE) of coating polymer powders. An important result was found that some of the samples examined were so sensitive that even a spark with a very low energy, such as 2 mJ, could ignite them. The values of the discharge spark energy of ignition testing set by the BSI (British Standards Institution) standards and the FM (Factory Mutual) regulations related to the safe operation of electrostatic powder coating systems are sufficiently high to result in the ignition of some of the coating powders. Therefore, it is imperative that more appropriate discharge spark energy values in testing be defined for safety assessment in electrostatic powder coating systems.
Modified Direct-Current Current-Voltage Method for Interface Trap Density Extraction in Metal-Oxide-Semiconductor Field-Effect-Transistor with Tunneling Gate Dielectrics at High Temperature
Authors: Zhu Shiyang , Nakajima Anri , Ohashi Takuo , Miyake Hideharu
Published: July 2005

For Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs) with a reduced gate oxide thickness, the large gate tunneling current overwhelms the direct-current current-voltage (DCIV) peak. Thus, the interface trap density (N
it) cannot be extracted from the conventional DCIV measurement. In this letter, a simple method of alleviating the gate tunneling component from the raw DCIV curves was studied and the N
it of MOSFETs with an ultrathin gate oxide was successfully extracted at arbitrary measurement temperatures. The extracted N
it was found to be independent of measurement temperature.
Experimental Evidence of Stability of Pt Clusters on and in Carbon Particles
Authors: Suzuki Hitoshi , Shintaku Masayuki , Sato Takeshi , Tamano Masayuki , Matsuura Toyoaki , Hori Michio , Kaito Chihiro
Published: July 2005

The stability of Pt clusters deposited on and embedded in carbon particles has been examined by in situ transmission electron microscopy. Commercial Pt clusters deposited on carbon particles began to move and coalesce upon heating above 150°C by surface melting coalescence, and the alterations were observed predominantly upon heating above 400°C. The embedded Pt clusters with the size of 1–3 nm disappeared by the diffusion of Pt atoms through the covered amorphous carbon layer upon heating above 1200°C. The Pt clusters embedded in carbon particles are more stable at higher temperatures about three times than the commercial Pt clusters deposited on carbon particles.
Selective Growth of Monoatomic Cu Rows at Step Edges on Si(111) Substrates in Ultralow-Dissolved-Oxygen Water
Authors: Tokuda Norio , Nishizawa Masayasu , Miki Kazushi , Yamasaki Satoshi , Hasunuma Ryu , Yamabe Kikuo
Published: July 2005

We have fabricated high-aspect-ratio monoatomic Cu rows along atomic step edges on vicinal Si(111) substrates. The method consists of two wet processes: (1) the formation of a step/terrace structure by immersing a Si(111) substrate in ultralow-dissolved-oxygen water (LOW) and (2) the formation of the nanowires by immersion in LOW containing Cu ions. A systematic investigation of Si(111) surfaces with the nanowire has been performed by means of atomic force microscopy, Fourier-transform infrared absorption spectroscopy, and total-reflection X-ray fluorescence spectroscopy.
Magnetometer Utilizing Cooled Normal Pickup Coil and High-TcSuperconducting Quantum Interference Device Picovoltmeter for Nondestructive Evaluation
Authors: Yang Tong Qing , Yao Kenichiro , Yamasaki Daisuke , Enpuku Keiji
Published: July 2005

A magnetometer utilizing a cooled normal pickup coil and a high-Tcsuperconducting quantum interference device (SQUID) picovoltmeter was applied to nondestructive evaluation in an unshielded environment. The pickup coil of copper wire was cooled toT=77 K in order to decrease thermal noise from resistance. The magnetic field noise of the magnetometer was 130 pT/Hz1/2and 10 pT/Hz1/2at 100 Hz and 1 kHz, respectively, for the pickup coil with a 4.4 mm diameter. It was shown that the magnetometer could be moved in an unshielded environment without degradation of its performance. By moving the cooled pickup coil, we successfully detected a small crack on the backsurface of the Cu plate in an unshielded environment.
Single-Mode Lasing in One-Dimensional Periodic Structure Containing Helical Structure as a Defect
Authors: Matsuhisa Yuko , Ozaki Ryotaro , Ozaki Masanori , Yoshino Katsumi
Published: July 2005

Laser action in a one-dimensional photonic crystal (PC) with dye-doped cholesteric liquid crystals as a defect layer has been investigated. A single-mode lasing has been achieved in the PC with a helical structure, which is based on the defect mode of the PC with a defect and the band edge effect of the cholesteric helix. The contribution of the interaction between the defect mode and band edge effects to the laser action was confirmed on the basis of the helix pitch dependence of lasing characteristics. The threshold of the laser action in the PC with the helical structure was lower than that in the helical structure without a PC. It has also been found that lasing wavelength shifts as a function of temperature corresponding to the band edge shift of the cholesteric liquid crystal.
Possibility of Computed Tomographic Reconstruction of Cracks from X-ray Refraction Contrast
Authors: Maksimenko Anton , Ando Masami , Sugiyama Hiroshi , Hashimoto Eiko
Published: July 2005

In recent years, X-ray refraction contrast has become a very powerful tool for nondestructive observations. It has great advantages over conventional absorption and phase-shift contrasts. The main advantage is the ability to visualize very tiny details such as cracks that are invisible in other contrasts. Therefore, the computed tomographic reconstruction from the refraction contrast is expected to have the same advantages. Here, we present the results of the refraction-based reconstruction which confirm these expectations. The structure of the sample containing cracks of submicron size was reconstructed. The cracks were proved to be clearly seen in the reconstructed images. Both 2D and 3D pictures of the reconstructed cracks are presented.
Silicon Single-Hole Transistor with Large Coulomb Blockade Oscillations and High Voltage Gain at Room Temperature
Authors: Harata Hidehiro , Saitoh Masumi , Hiramoto Toshiro
Published: July 2005

We propose a new approach for realizing single-electron and single-hole transistors with both large Coulomb blockade oscillations and high voltage gain at room temperature. A thin gate oxide is adopted to increase gate capacitance and ultra-narrow channel is formed to reduce source and drain capacitance. The fabricated single-hole transistor shows large Coulomb blockade oscillations with peak-to-valley-current-ratio of 32 and high voltage gain of as high as 4.7 at room temperature. This is the first demonstration of room-temperature operating single-hole transistor with high voltage gain. The inverter circuit gain is also calculated on the basis of the experimental results, and the gain exceeds unity.
Blue Light-Emitting Diode Based on ZnO
Authors: Tsukazaki Atsushi , Kubota Masashi , Ohtomo Akira , Onuma Takeyoshi , Ohtani Keita , Ohno Hideo , Chichibu Shigefusa F. , Kawasaki Masashi
Published: July 2005

A near-band-edge bluish electroluminescence (EL) band centered at around 440 nm was observed from ZnOp–i–nhomojunction diodes through a semi-transparent electrode deposited on thep-type ZnO top layer. The EL peak energy coincided with the photoluminescence peak energy of an equivalentp-type ZnO layer, indicating that the electron injection from then-type layer to thep-type layer dominates the current, giving rise to the radiative recombination in thep-type layer. The imbalance in charge injection is considered to originate from the lower majority carrier concentration in thep-type layer, which is one or two orders of magnitude lower than that in then-type one. The current-voltage characteristics showed the presence of series resistance of several hundreds ohms, corresponding to the current spread resistance within the bottomn-type ZnO. The employment of conducting ZnO substrates may solve the latter problem.
DC and RF Characteristics in Al2O3/Si3N4 Insulated-Gate AlGaN/GaN Heterostructure Field-Effect Transistors
Authors: Maeda Narihiko , Makimura Takashi , Maruyama Takashi , Wang Chengxin , Hiroki Masanobu , Yokoyama Haruki , Makimoto Toshiki , Kobayashi Takashi , Enoki Takatomo
Published: July 2005

Al2O3/Si3N4 insulated-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) have been fabricated, where excellent RF characteristics have been obtained in addition to the low gate leakage current as the result of employing the metal–insulator–semiconductor (MIS) structure. In an HFET with a gate length (L
g) of 0.1 µm, the cutoff frequency ( f
T) and maximum oscillation frequency ( f
max) were estimated to be 70 and 90 GHz, respectively. The drain current density (I
d) and transconductance (g
m) were 1.30 A/mm and 293 mS/mm, respectively. The gate leakage current (I
g) was as low as 4×10-5 A/mm even at a forward bias voltage of +3 V.
Strongly Enhanced Phosphor Efficiency in GaInN White Light-Emitting Diodes Using Remote Phosphor Configuration and Diffuse Reflector Cup
Authors: Kim Jong Kyu , Luo Hong , Schubert Eric Fred , Cho Jaehee , Sone Cheolsoo , Park Yongjo
Published: July 2005

Enhancement of phosphor efficiency is reported for GaInN-based white light-emitting diodes (LEDs) employing a large separation between the primary LED emitter and the wavelength converter, and a diffuse reflector cup. Ray-tracing simulations show that extraction efficiency of wavelength-converted light is enhanced by 75%. The experimental improvement in phosphor efficiency of blue-pumped yellow phosphor is 15.4% compared with conventional phosphor-based white LEDs. The improvement is attributed to reduced re-absorption of wavelength-converted light by the LED chip.
Tunable Sub-Terahertz Wave Generation from an Organic DAST Crystal
Authors: Taniuchi Tetsuo , Ikeda Satoshi , Okada Shuji , Nakanishi Hachiro
Published: July 2005

Tunable sub-terahertz (THz) waves ranging from 0.3 to 3 THz were generated in a 4'-N,N-dimethylamino-N'-methyl-4-stilbazolium tosylate (DAST) crystal using the difference frequency mixing technique. We developed a dual-wavelength optical parametric oscillator near 990 nm with two KTiOPO4 crystals as the input light source. The maximum output energy of 17 nJ/pulse (peak power: 1.4 W) was achieved at 0.7 THz using a high-quality DAST crystal with a 2-mm thickness.
Influence of k·p Formalisms on the Band Structure of InxGa1-xAs1-yNy/GaAs Quantum Well: A Comparison of 8-Band and 10-Band Models
Authors: Ng Say Tyam , Fan Wei Jun , Dang Yu Xing , Yoon Soon Fatt
Published: July 2005

The influence of two k·p formalisms, namely, the realistic 8-band and 10-band models, on the conduction and valence band structures of a 7 nm In
x
Ga1-x
As1-y
N
y
/GaAs quantum well (QW) has been investigated. It is discovered that at high indium composition (35%), the energy dispersion curves calculated by the 8-band model, using electron effective mass (m
e
*) predicted by band-anticrossing (BAC) model, agrees very well with the results of 10-band model near the Brillouin zone center. However, at lower indium composition (15%), larger deviation of excited state energy level, such as e2, is found. In contrast to the previous reports that assume great enhancement of m
e
* even at indium of 30–40%, m
e
* extrapolated from the BAC model predicted a more modest enhancement that is weakened as the indium composition in the well layer is being increased.
Preferred Orientation and Anisotropic Growth in Polycrystalline ZnO:Al Films Prepared by Magnetron Sputtering
Authors: Fenske Frank , Selle Burkhardt , Birkholz Mario
Published: July 2005

A thorough growth study of thin polycrystalline ZnO:Al samples prepared by DC magnetron sputtering is presented. The atomic areal density as a function of deposition timetwas determined by Rutherford backscattering (RBS), from which a growth rateG(t) can be defined. It was found, that in the initial stages of film growthG(t) increases with increasing deposition time up to a thickness of about 300 nm, although the process conditions were kept constant. In addition, the preferred orientation of each sample, as characterized by a <00.l> fiber texture, was quantified by evaluating the texture indexJfor each sample. The course ofJ(t) was identified to concomitantly increase withG(t). The variation of both, growth rate and preferred orientation, with deposition time is interpreted to be caused by an anisotropic growth velocity of ZnO grains. It seems that such a close correlation between growth rate and texture has not been observed so far.
Surface-Micromachined Optical Interferometry System Utilizing Three-Dimensional Micromirrors and Microgratings
Authors: Kuo Ju-Nan , Lee Gwo-Bin , Pan Wen-Fung
Published: July 2005

This paper presents a novel micro-optical interferometer incorporating three-dimensional micromirrors and microgratings. The interferometry system comprises a fixed grating mirror, two rotatable reflection mirrors, and a movable grating mirror driven by an electrostatically actuated oscillating structure. The use of a curved polysilicon structure lowers the electrostatic operating voltage (4 V) of the oscillating structure substantially and permits high-speed movement (2 kHz) of the grating. The novel system presented in this study provides a wider modulation frequency, and hence a wider frequency response. Furthermore, the proposed micro-optical interferometer can be applied to a micro-optical bench to facilitate signal modulation and precision measurement applications.
Growth of Y1Ba2Cu3Ox Single-Crystal Whisker Using Sb-doped Precursor
Authors: Nagao Masanori , Yun KyungSung , Nakane Takayuki , Wang Huabing , Takano Yoshihiko , Hatano Takeshi , Yamashita Tsutomu , Tachiki Masashi , Maeda Hiroshi , Sato Mitsunori
Published: July 2005

Single-crystal whiskers of Y1Ba2Cu3O
x
with a length of approximately 4 mm were grown from an Sb-doped precursor. The optimum nominal composition of precursors in this Sb-doping method is Y2Ba2.75Cu3Sb0.5O
x
. Sb is not detected in the whiskers by energy-dispersive X-ray spectroscopy. The standard 4-probe transport measurements for the as-grown whiskers show a critical temperature T
C of approximately 90 K and a c-axis critical current density J
C of 6.57 ×104 A/cm2 at 89 K.
Feasibility of Electron Density Measurement Using Relativistic Downshift Frequency Effect of Electron Cyclotron Emission in Tokamak Plasmas
Authors: Sato Masayasu , Isayama Akihiko , Iwama Naofumi , Kawahata Kazuo
Published: July 2005

The feasibility of electron density measurement using the relativistic downshift frequency effect of electron cyclotron emission in tokamak plasmas has been studied by numerical calculation. It is found that electron density measurement can be performed by observing the frequency shift from the nonrelativistic electron cyclotron frequency. The frequency shift is large when the observation is carried out from the high-field-side of torus. As this large frequency shift depends mainly on electron temperature and density, electron density can be determined while electron temperature is obtained from the observation of the low-field-side.
Frequency Tunable Circular Polarization Control of Terahertz Radiation
Authors: Shimano Ryo , Nishimura Hisaaki , Sato Tomohiro
Published: July 2005

We report on frequency tunable circular polarization control of THz radiation. The technique is based on the relative phase control of two THz pulses that are generated from optical rectification of ultrashort optical pulses in a ZnTe crystal. By changing the temporal separation of the optical pump pulses, continuous control of circular polarization from right to left is achieved in the frequency range from 0.3 to 2.5 THz. The developed scheme shows a potential application for sensitive detection of circular dichroism in the far-infrared regime.
Progress in the Efficiency of Wide-Gap Cu(In1-xGax)Se2 Solar Cells Using CIGSe Layers Grown in Water Vapor
Authors: Ishizuka Shogo , Sakurai Keiichiro , Yamada Akimasa , Shibata Hajime , Matsubara Koji , Yonemura Minoru , Nakamura Satoshi , Nakanishi Hisayuki , Kojima Takeshi , Niki Shigeru
Published: July 2005

Progress in the performance of wide-gap Cu(In1-x
Ga
x
)Se2 (CIGSe) solar cells for x values around 0.5 has been demonstrated using CIGSe layers grown in the presence of water vapor. While CIGSe thin films deposited in the presence of water vapor showed variations in electrical properties such as increases in hole carrier density and a consequent enhancement of p-type conductivity, no significant changes in the morphology and growth orientation were observed. Both the open circuit voltages and current densities of the CIGSe solar cells were improved using CIGSe layers grown in water vapor. An 18.1%-efficient cell with an open circuit voltage of 0.744 V, a current density of 32.4 mA/cm2 and a fill factor of 0.752 was fabricated from a 1.3 eV-CIGSe (x ∼0.48) layer.
Incubation-Free Growth of Polycrystalline Si Films by Plasma-Enhanced Chemical Vapor Deposition Using Pulsed Discharge under Near Atmospheric Pressure
Authors: Kitabatake Hirotatsu , Suemitsu Maki , Kitahata Hiroya , Nakajima Setsuo , Uehara Tsuyoshi , Toyoshima Yasutake
Published: July 2005

By using the plasma-enhanced chemical vapor deposition (PE-CVD) under near-atmospheric pressures, we have achieved a high rate growth, 1 nm/s, of polycrystalline Si films on glass substrates without incubation layers for the first time. We have employed a short-pulse based system for a stable operation of discharge at atmospheric pressures without inert gas dilution. This feature enabled us to employ an extremely high dilution of monosilane by hydrogen, which should be the origin of the incubation-free growth of our films, in addition to the basic advantage for the high rate growth inherent in atmospheric reaction systems. The films are mainly consisted of polycrystalline Si with grain size ranging from 5 nm to above 10 nm, as observed by Raman scattering, X-ray diffractions and cross sectional transmission electron microscopy.
Welding of Transparent Materials Using Femtosecond Laser Pulses
Authors: Tamaki Takayuki , Watanabe Wataru , Nishii Junji , Itoh Kazuyoshi
Published: July 2005

We report on laser welding between transparent materials without the insertion of intermediate layers such as glue by use of near-infrared femtosecond laser pulses. When femtosecond laser pulses are focused at the interface of transparent materials, the material around the focal point is melted and resolidified because of the temperature increases due to the localized nonlinear absorption of optical pulse energy. We experimentally succeeded in laser welding between two pieces of silica glass without the insertion of an intermediate layer by femtosecond laser pulses. This technique has a possible application to the joining of semiconductors such as silicon crystals.
High-Rate Growth of Films of Dense, Aligned Double-Walled Carbon Nanotubes Using Microwave Plasma-Enhanced Chemical Vapor Deposition
Authors: Hiramatsu Mineo , Nagao Hidetoshi , Taniguchi Masaki , Amano Hiroshi , Ando Yoshinori , Hori Masaru
Published: July 2005

Carbon nanotube (CNT) films were grown using microwave plasma-enhanced chemical vapor deposition. Catalytic cobalt (Co) nanoparticles were deposited on a silicon substrate using pulsed arc deposition. A titanium nitride (TiN) thin film was used as a buffer layer on the substrate in order to prevent the formation of Co silicide. A dense, vertically aligned, double-walled CNT (DWNT) film was grown rapidly on the Co-catalyzed Si substrate. The CNTs grew at an extremely high rate of 600 nm/s during the first 10 min of growth. Dense DWNT films with thicknesses of over 500 µm were obtained in 20 min.
Growth of InAsSb Quantum Dots on GaAs Substrates Using Periodic Supply Epitaxy
Authors: Ueta Akio , Gozu Sin-ichioro , Akahane Kouichi , Yamamoto Naokatsu , Ohtani Naoki
Published: July 2005

InAsSb quantum dots (QDs) were studied by introducing periodic supply epitaxy. Photoluminescence spectra from InAsSb QDs showed strong emissions even at room temperature. The InAsSb QDs by periodic supply epitaxy allowed the control of emission wavelengths of optical fiber communication systems. The control of the density of InAsSb QDs in the range from 4.5 ×109 to 3.5 ×1010 cm-2 without changing emission wavelengths was demonstrated. These results indicate that periodic supply epitaxy is a useful technique for various optical devices such as QD lasers and single photon emitters.
Improvement in UV Optical Properties of CsLiB6O10 by Reducing Water Molecules in the Crystal
Authors: Nishioka Muneyuki , Kanoh Ai , Yoshimura Masashi , Mori Yusuke , Sasaki Takatomo , Katsura Tomotaka , Kojima Tetsuo , Nishimae Junichi
Published: July 2005

We investigated the effects of water molecules in CsLiB6O10 (CLBO) crystals on UV optical properties. Our results show that long-term heat treatment is necessary to adequately remove water molecules from inside the crystal. The reducing the number of water molecules contained in the crystal improves the transmittance at 266 nm. In addition, the long-term heat-treated crystal can generate three-times higher 266-nm output without bulk damage than a normal sample.
Epitaxial Growth of GaN on (1 0 0) β-Ga2O3 Substrates by Metalorganic Vapor Phase Epitaxy
Authors: Shimamura Kiyoshi , Víllora Encarnación G. , Domen Kay , Yui Keiichi , Aoki Kazuo , Ichinose Noboru
Published: July 2005

Epitaxial growth of nitride compounds by the metalorganic vapor phase epitaxy (MOVPE) technique is demonstrated for the first time on β-Ga2O3 single crystal substrates, which are near-UV transparent and n-type conductive. High-quality (0 0 0 1) GaN epi-layer with a narrow bandedge luminescence was obtained using a low temperature conductive buffer layer. InGaN multi-quantum well (MQW) structure was also successfully grown. The first blue light-emitting diode (LED) on β-Ga2O3 with vertical current injection is demonstrated.
Photoluminescence and its Enhancement of Pr3+-Doped BaTiO3 Phosphor
Authors: Li Juan , Wu Yong Jun , Kuwabara Makoto
Published: July 2005

We succeeded in developing a new praseodymium (Pr3+)-doped BaTiO3 phosphor with the addition of Mg, which exhibits a strong red emission, using a high-concentration sol–gel process in which the obtained gel was fired at 1200°C for 2 h. The photoluminescence is due to intra-4f transitions of Pr3+, mainly from the excited states 1D2 to the ground states of 3H4. An approximately 60 fold enhancement of light emission in 0.1 mol% Pr-doped BaTiO3 was achieved by adding 0.5 mol% Mg. This emission enhancement is discussed on the basis of the increments of effective energy transfer between the overlapped absorption band of BaTiO3 and the 4f–5d band of Pr3+, and on the effective charge compensation by the addition of Mg.
New Characteristic Equation of Three-Dimensional Integral Imaging System and its Applications
Authors: Min Sung-Wook , Kim Joohwan , Lee Byoungho
Published: July 2005

A three-dimensional integral imaging system is analyzed using the viewing parameters, namely, the image resolution, the viewing angle and the image depth. A new characteristic equation of this integral imaging system, which shows the relationship among the viewing parameters, is presented. This characteristic equation can be adopted as a design criterion for the integral imaging system. This can also be used as a figure of merit for the quantitative analysis of the integral imaging system.
Epitaxial Growth of Ferromagnetic Fe3Si Films on CaF2/Si(111) by Molecular Beam Epitaxy
Authors: Sunohara Tsuyoshi , Kobayashi Ken'ichi , Umada Masakazu , Yanagihara Hideto , Kita Eiji , Akinaga Hiroyuki , Suemasu Takashi
Published: July 2005

Ferromagnetic Fe3Si/CaF2 hybrid structures were epitaxially grown on Si(111) by molecular beam epitaxy. When Si and Fe were directly deposited on the Si substrate, it was difficult to prevent inclusion of FeSi in the grown films. This problem was overcome by forming a CaF2 epitaxial film on Si(111) first, followed by codeposition of Si and Fe to form Fe3Si. Fe3Si films were epitaxially grown on the CaF2 at 400°C. A distinct square-like hysteresis loop was observed at room temperature in the magnetic field dependence of Kerr rotation.
Detection of Hypochlorous Acid Using Reduction Wave During Anodic Cyclic Voltammetry
Authors: Kodera Fumihiro , Umeda Minoru , Yamada Akifumi
Published: July 2005

A novel analysis method for detecting low free-chlorine concentrations using a reduction wave based on anodic cyclic voltammetry has been developed. The reduction wave has been observed at approximately 600 mV vs Ag/AgCl, which is dependent on the free-chlorine concentration and switching potential. The wave peak showed a maximum value for the switching potential at approximately 1350 mV vs Ag/AgCl, and a good linear relationship between the peak current and the concentrations in the range of 0.2–6.0 mg dm-3. The relative standard deviation (RSD) at each concentration was less than 2%. This method seems to be useful for the analysis of low free-chlorine concentrations.
Unique Multilevel Flash Memory Devices Operating at High Programming Speed, Designed Utilizing Novel Asymmetric Gates
Authors: Kwon Man Gu , Kim Jae Ho , Kim Tae Whan , Kwack Kae Dal
Published: July 2005

Unique multilevel cell (MLC) flash memory devices utilizing novel asymmetric gates were proposed to enhance a writing time. Different coupling ratios and maximum storage charges of the MLC flash memories with the asymmetric floating gates decreased the number of step pulses for the storage of the multi-bits in each memory cell. These results indicate that the writing time of the MLC flash memories can be improved by using the asymmetric floating gate structure consisting of the different coupling ratio and the maximum storage charge in the floating gates.
Sensitization of Nanocrystalline SnO2Films with Indoline Dyes
Authors: Onwona-Agyeman Boateng , Kaneko Shoji , Kumara Asoka , Okuya Masayuki , Murakami Kenji , Konno Akinori , Tennakone Kirthi
Published: July 2005

Using newly synthesized indoline dyes as sensitizers for photoelectrochemical solar cells based on SnO2nanocrystalline films, an energy conversion efficiency of 2.8% is achieved, compared with 1.2% for ruthenium bipyridyl dye (N-719) under the same experimental conditions. It is suggested that the formation of nonquenching aggregates and the better passivation of surface states on SnO2by indoline dyes are instrumental factors in giving a higher efficiency for the cell sensitized with this dye.
Two-Dimensional Distributions of Ti and Ti+ Densities in High-Pressure Magnetron Sputtering Discharges
Authors: Nafarizal Nayan , Takada Noriharu , Shibagaki Kanji , Nakamura Keiji , Sago Yasumi , Sasaki Koichi
Published: July 2005

We measured two-dimensional distributions of Ti and Ti+ densities in magnetron sputtering plasmas by laser-induced fluorescence (LIF) imaging spectroscopy. It has been found that the production of Ti+ is enhanced by a high gas pressure. The peak of the Ti+ density is located at a distance of 4–5 cm from the target surface, indicating the gas-phase production of Ti+ in the downstream plasma. Since the plasma density and the electron temperature measured using a Langmuir probe are low in the downstream plasma, this result suggests that the dominant production process of Ti+ is not electron impact ionization of Ti (Ti+e→Ti+e+e). Although another candidate for the gas-phase production of Ti+ is Penning ionization (Ti+ArM→Ti++Ar+e), experimental results on ArM is negative about the contribution of Penning ionization to the gas-phase production of Ti+.
Direct Drawing of Ag Microwiring by Laser-Induced Pyrolysis of Film Prepared from Liquid-Dispersed Metal Nanoparticles
Authors: Watanabe Akira , Kobayashi Yoshio , Konno Mikio , Yamada Shinji , Miwa Takao
Published: July 2005

Ag microwiring with submicron resolution was fabricated by the laser-induced pyrolysis of a film prepared from liquid-dispersed Ag nanoparticles. The linewidth of the wiring fabricated by this laser direct-write maskless technique can be controlled flexibly by the laser beam focusing conditions. The resistivity of the Ag wiring fabricated by this technique (1.9×10-6 Ω cm) is comparable with that of bulk Ag (1.6×10-6 Ω cm).
In situ Transmission Electron Microscopy of Field-Emitting Bundles of Double-Wall Carbon Nanotubes
Authors: Seko Kazuyuki , Kinoshita Jun-ichi , Saito Yahachi
Published: July 2005

The dynamic behavior and degradation of carbon nanotube field emitters were studied by in situ transmission electron microscopy. The carbon nanotube emitters used for the study were double-wall nanotubes (DWNTs) produced by arc discharge. The DWNTs formed bundles, each of which contained about seven DWNTs. The splitting of a bundle into two branches, forming a “Y” shape, accompanied by an abrupt increase of emission current, was observed in real time. The shortening of bundles, presumably due to Joule heating, was also observed. The maximum emission current from a bundle just before its sublimation was at least 10 µA, which corresponds to 1.4 µA per single DWNT.
RF Microplasma Jet at Atmospheric Pressure: Application to Rapid Recrystallization of Amorphous Silicon
Authors: Sakurai Yusuke , Kobayashi Tomohiro , Hasegawa Yasuhiro , Shirai Hajime
Published: July 2005

A novel rapid recrystallization technique for amorphous silicon (a-Si) utilizing an rf microplasma jet of argon at atmospheric pressure is presented. A highly crystallized polycrystalline silicon film (poly-Si) was synthesized uniformly by the rapid plasma annealing of a-Si films deposited on glass and aluminum plates by translating the substrate stage at 0.05–250 mm/s. X-ray diffraction analysis, Raman scattering and I–V measurements demonstrated that 0.3–3-µm-thick a-Si samples could be fully crystallized below several milliseconds. Film crystallinity is discussed in terms of the traveling velocity of the substrate stage, the flow rate of argon, and the thickness of as-deposited a-Si films.
Annealing Temperature Dependence on Nickel–Germanium Solid-State Reaction
Authors: Zhu Shiyang , Nakajima Anri
Published: July 2005

The solid-state reaction of nickel and germanium was performed by isochronous vacuum annealing at temperatures ranging from 250 to 600°C. The reaction starts at 250°C to form poly-crystalline Ni–monogermanide (NiGe), and it substantially occurs at 350°C. The NiGe surface roughness, as well as the NiGe grain size, increases with increasing the annealing temperature from 400 to 600°C. All nickel germanide/n-Ge Schottky contacts has a similar Schottky barrier height around 0.47–0.48 eV due to the Fermi level pinning effect.
Ultra-Shallow Junction Formation by Green-Laser Annealing with Light Absorber
Authors: Takii Eisuke , Eto Takanori , Kurobe Ken-ichi , Shibahara Kentaro
Published: July 2005

Laser annealing with nano-seconds pulse width is expected to be a useful tool for ultra-shallow junction formation. To compensate for the deep penetration depth of green laser light into Si, a metal absorber was placed on a specimen. The absorber was effective in reducing the laser energy density required to activate dopant. However, absorber formation that resulted in over-melt that increased junction depth easily occurred compared with specimens without the absorber. This problem was attributable to the absence of the increase in reflectivity by surface Si melting.
Mutual Inductance Coupled through Superconducting Thin Film in Niobium Josephson Integrated Circuits
Authors: Mizugaki Yoshinao , Hakii Hidemitsu , Moriya Masataka , Usami Kouichi , Kobayashi Tadayuki
Published: July 2005

We present numerical and experimental investigation on mutual inductance coupled through a superconducting Nb thin film. The inductance extraction program FastHenry with superconductor support is used for numerical calculation. The self- and mutual inductances of two superconducting strip lines are calculated as functions of the width of the shield layer inserted between them. The results demonstrate that the mutual coupling is reduced with increasing shield layer width. A superconducting quantum interference method is employed to measure the mutual inductance on Nb IC chips. The experimental results of the mutual inductance agree with the calculated results.
Characteristics of Charging Effect in One-Dimensional Array of Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions
Authors: Kawae Takeshi , Yasuda Takashi , Awaji Satoshi , Nakajima Kensuke , Hatano Takeshi , Yamashita Tsutomu
Published: July 2005

For the observation of the charging effect on a Josephson junction, the charging energy (E
c) must be much larger than the Josephson coupling energy (E
J) and thermal energy (k
B
T). We investigated the properties of submicron-sized Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions (IJJs) at low temperature. The current–voltage curve of IJJs with a junction area of 0.06 µm2 showed a much higher resistance state near the zero bias voltage regions when the measurement temperature decreased to 72.6 mK. The ratios of E
c/E
J and E
c/k
B
T were 7.04 and 5.78, respectively, which indicates that the charging effect is dominant. In addition, a characteristic voltage structure due to the charging effect in one-dimensional junction array, which is composed of the offset voltage and the threshold voltage of the junction, was observed.
Optimization of Annealing Time and Cu Concentration for Study of Luminescence Properties of Cu-Implanted ZnO Thin Films
Authors: Sakaguchi Isao , Ryoken Haruki , Sato Yoshiyuki , Hishita Syunichi , Ohashi Naoki , Saito Noriko , Haneda Hajime
Published: July 2005

New ion implantation techniques were applied to optimize conditions such as annealing time, Cu dose, and Cu concentration for the green emission originating from Cu phosphor in ZnO thin films. Copper ions accelerated to 150 keV were implanted at room temperature. In the ZnO thin films implanted with Cu, the suitable annealing time was 90 min at 800°C. The optimal Cu dose was determined to be 4.5 ×1014 ions/cm2. The ZnO thin films optimized for effective green emission had a Cu concentration of 9 ×1018 ions/cm3.
Development of Compact C2F4 Gas Supply Equipment and Its Application to Etching of Dielectrics in an Environmental Benign Process
Authors: Takahashi Shunji , Den Shoji , Katagiri Toshirou , Yamakawa Koji , Kano Hiroyuki , Hori Masaru
Published: July 2005

Compact C2F4 gas supply equipment, which controls the gas supply with sufficient accuracy by irradiation of a carbon dioxide laser (CO2) onto a solid source (PTFE) without using any fluorocarbon gas, has been developed to combat global warming. Although C2F4 gas has a very low Global Warming Potential (GWP <1), it is very unstable and thus considerably difficult to handle. This gas is used in the semiconductor manufacture process, where it is obtained from a conventional high-pressure cylinder. By changing the output of the laser, the amount of C2F4 gas generated can be precisely controlled in this equipment while also ensuring safety. The gas is supplied to the VHF excited parallel plate plasma reactor through a gas shower head with Ar carrier gas and, in actual tests, this environmental benign technology achieved high etching performances for low-k SiOCH and SiO2 films.
X-ray Interference Fringe in Bragg–(Bragg)m–Laue Case from Thin Finite Crystal
Authors: Fukamachi Tomoe , Negishi Riichirou , Yoshizawa Masami , Kawamura Takaaki
Published: July 2005

In an absorbing thin finite crystal, part of the incident X-rays can be confined in the Bragg–(Bragg)
m
–Laue case. The confined beams are repeatedly diffracted in the crystal and come out of its edge surface. An X-ray interference fringe, which is caused by a sequence of diffractions between the top and bottom surfaces during the confinement, is observed in the beams emitted in both the reflection and transmission directions. The characteristic features of the fringe measured using synchrotron radiation are studied.
In situ Conductance Measurement of a Limited Number of Nanoparticles during Transmission Electron Microscopy Observation
Authors: Hirose Ryusuke , Arita Masashi , Hamada Kouichi , Takahashi Yasuo , Subagyo Agus
Published: July 2005

A technique for measuring the conductance of a small number of particles during transmission electron microcopy (TEM) observation is demonstrated. By using a custom-designed TEM holder, an Au tip was brought into contact with Fe nanodots contained in a SrF2 film deposited on another Au tip. The conductance shows Coulomb-blockade-like characteristics even at room temperature.
Photon Antibunching Observed from an InAlAs Single Quantum Dot
Authors: Kimura Satoshi , Kumano Hidekazu , Endo Michiaki , Suemune Ikuo , Yokoi Tomonori , Sasakura Hirotaka , Adachi Satoru , Muto Shunichi , Song Hai Zhi , Hirose Shinichi , Usuki Tatsuya
Published: July 2005

Single-photon emitters and detectors are key devices to realize secure communications with single-photon-based quantum cryptography and single-photon-based quantum computing. InAlAs quantum dots (QDs) cover the wavelength range with high quantum efficiencies of Si-based single-photon detectors. Clear photon antibunching was observed from an InAlAs single QD under weak excitations. To realize single-photon emitters on demand, complete population of the QD energy states before the photon emission events is necessary, but the measured antibunching properties were dependent substantially on the photo-excitation powers. The physical origin of this problem is discussed. The criterion to distinguish the real deviation from the photon antibunching condition and the artifact of the measurements is clarified. The capability of single-photon emissions on demand will be demonstrated with photon antibunching under pulsed operations.
Structural Characterization of Thick GaN Films Grown on Free-Standing GaN Seeds by the Ammonothermal Method Using Basic Ammonia
Authors: Hashimoto Tadao , Fujito Kenji , Wu Feng , Haskell Benjamin A. , Fini Paul T. , Speck James S. , Nakamura Shuji
Published: July 2005

Single crystalline GaN was grown on c-plane free-standing GaN seeds via fluid transport by the ammonothermal method. Ammonothermal growth was carried out in an ammonobasic solution with a metallic Ga nutrient placed in a lower-temperature zone. The thickest film obtained so far is ∼45 µm, which was grown on the N-face of the seed. The growth interface contained numerous voids and defects, whereas the microstructure close to the surface was greatly improved. The major defects close to the surface were mixed-character threading dislocations. The estimated threading dislocation density was low-109 cm-2 level at the free surface of the N-face.
Nucleation Stages of Carbon Nanotubes on SiC(0001) by Surface Decomposition
Authors: Hayashi Kenjiro , Mizuno Seigi , Tanaka Satoru , Toyoda Hiroki , Tochihara Hiroshi , Suemune Ikuo
Published: July 2005

Nucleation stages of carbon nanotubes (CNTs) on a SiC(0001) Si-face (4° off toward [1120 ]) by surface decomposition are investigated by means of in-situ scanning tunneling microscopy (STM). After a relatively short heating time at 1600°C, moiré patterns and small nuclei appear on the surface due to the evaporation of Si atoms and, as a result of this, surface graphitization. Modelling of the moiré pattern indicates the formation of a single graphene sheet on top of the SiC surface. Local swelling (∼1 nm in diameter) of such a graphene sheet, possibly resulting from the compressive stress at the graphene/SiC interface, gives rise to a CNT nucleus. In the stages that follow, the nucleus is continuously and unidirectionally prolonged and rolled-up, which may result in a final form such as a CNT.
Growth of Thick 4H–SiC(0001) Epilayers and Reduction of Basal Plane Dislocations
Authors: Tsuchida Hidekazu , Kamata Isaho , Miyanagi Toshiyuki , Nakamura Tomonori , Nakayama Koji , Ishii Ryousuke , Sugawara Yoshitaka
Published: July 2005

We investigate basal plane dislocations (BPDs) in thick 4H–SiC(0001) epilayers and the formation of stacking faults in the active region of pin diodes. Synchrotron reflection X-ray topography shows that epitaxial growth on (0001) is advantageous in preventing the propagation of BPDs from the substrate into the epilayer and obtaining a low BPD density in the epilayer compared with growth on (0001). The current stress test of 4H–SiC(0001) pin diodes demonstrates the suppressed formation of stacking faults.
(100)-Oriented 3C–SiC Polycrystalline Film Grown on SiO2 by Hot-Mesh Chemical Vapor Deposition Using Monomethylsilane and Hydrogen
Authors: Narita Yuzuru , Yasui Kanji , Eto Jumpei , Kurimoto Taishi , Akahane Tadashi
Published: July 2005

To fabricate a SiC-on-insulator (SiCOI) structure, the growth of cubic silicon carbide (3C–SiC) polycrystalline films on thermally oxidized Si (SiO2/Si) substrates by hot-mesh chemical vapor deposition (HMCVD) utilizing high-density hydrogen radicals was investigated. The SiC films were grown at low temperatures below 900°C using monomethylsilane (MMS) as a source gas. On the basis of growth activation energy, the rate-determining step of SiC growth below 850°C was considered to be the supply of hydrogen radicals from a tungsten (W) mesh surface. From X-ray diffraction measurements, the growth of (100)-oriented 3C–SiC films was determined to be achieved at a substrate temperature of 750°C, while that of polycrystalline SiC films, at substrate temperatures above 850°C.
Studies of Electron Beam Evaporated SiO2/AlGaN/GaN Metal–Oxide–Semiconductor High-Electron-Mobility Transistors
Authors: Arulkumaran Subramaniam , Egawa Takashi , Ishikawa Hiroyasu
Published: July 2005

The metal–oxide–semiconductor high-electron-mobility transistors (MOSHEMTs) have been demonstrated and its dc characteristics were examined and compared with the conventional AlGaN/GaN HEMTs. The electron beam (EB) evaporated SiO2 layers were used as a gate-insulator. Capacitance–voltage plot of MOS contacts revealed the existence of injection type complete accumulation up to +4.0 V. The fabricated MOSHEMTs have exhibited better dc characteristics when compared with the conventional AlGaN/GaN HEMTs. The MOSHEMTs could operate at positive gate-biases as high as +4.0 V. The 2.0-µm-gate-length EB-SiO2 MOSHEMTs exhibited higher drain current density and extrinsic transconductance of 856 mA/mm and 145 mS/mm when compared to the conventional AlGaN/GaN HEMTs. The gate leakage current (I
gLeak) was three orders of magnitude lower than that of the conventional AlGaN/GaN HEMTs. The stable device operations at high operating voltages with low I
gLeak and high g
mmax values leads to the occurrence of low trap density at EB-SiO2/AlGaN interface.
Ion Irradiation Control of Ferromagnetism in (Ga,Mn)As
Authors: Kato Hiroaki , Hamaya Kohei , Taniyama Tomoyasu , Kitamoto Yoshitaka , Munekata Hiro
Published: July 2005

We report on a promising approach to the artificial modification of ferromagnetic properties in (Ga,Mn)As using a Ga+ focused ion beam (FIB) technique. The ferromagnetic properties of (Ga,Mn)As such as magnetic anisotropy and Curie temperature can be controlled using Ga+ ion irradiation, originating from a change in hole concentration and the corresponding systematic variation in exchange interaction between Mn spins. This change in hole concentration is also verified using micro-Raman spectroscopy. We envisage that this approach offers a means of modifying the ferromagnetic properties of magnetic semiconductors on the micro- or nano-meter scale.