bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Interfaces on Crystal Growth of Si in SiO2/a-Si/SiO2 Layered Structures
Authors: Tagami Takashi , Yutaka Wakayama Yutaka Wakayama , Shun-ichiro Tanaka Shun-ichiro Tanaka
Published: October 2002

The crystal growth of Si in SiO2/a-Si/SiO2 layered structures is examined by high resolution transmission electron microscopy. In a thin a-Si layer (10 nm), crystal growth halts with the crystallite size roughly equal to the layer thickness. In a thick layer (50 nm), crystal growth continues beyond the layer thickness. An expression for this halt in growth is derived from the free energy change. The halt in growth of Si crystallites suggests that the a-Si/SiO2 interface and the a-Si/c-Si interface are more stable than the c-Si/SiO2 interface.
Highly Reflective 1.55 µmIn1-x-yGaxAlyAs/In1-zAlzAs Quaternary Bragg Mirrors Grown by Metalorganic Chemical Vapor Deposition (MOCVD)
Authors: Sung-Woo Choi Sung-Woo Choi , Hyung-Moo Park Hyung-Moo Park
Published: October 2002

High reflectivity In1-
x
-
y

Ga

x

Al

y

As/In1-
z

Al

z

As quaternary Bragg mirrors operating at 1.55 µ m have been grown on InP substrates by metalorganic chemical vapor deposition. In situ laser beam reflectometry has been applied to monitor the Bragg layer thickness in real time for precise and reproducible growth. The In0.53Ga0.41Al0.06As/In0.52Al0.48As mirrors exhibit a reflectivity of 86% for 10 periods, and 99% for 25 periods, respectively. A highly accurate position with respect to the designed band center wavelength at 1.55 µ m has been achieved for the quaternary Bragg mirrors.
Fabrication of NdBa2Cu3O7-δ (110)-(001) Grain Boundary Josephson Junction by Focused Ion Beam Method
Authors: Mizuno Yuuji , Ishimaru Yoshihiro , Jianguo Wen Jianguo Wen , Youichi Enomoto Youichi Enomoto
Published: October 2002

A needle-like a-axis oriented grain is artificially grown in a c-axis oriented NdBa2Cu3O7-δ (NBCO) thin film. Its long direction is parallel to the [110] direction of a (001) MgO substrate on a small rectangular area damaged by a focused Ga ion beam. The transmission electron microscopy (TEM) lattice image shows an atomically flat grain boundary and the lattice configuration of the grains. The boundary junction of the needle-like grain shows no supercurrent at zero magnetic field. However, an RSJ-type I-V curve with the supercurrent is observed under finite magnetic field. In addition, Shapiro steps are observed under microwave irradiation, indicating that the junction works as a Josephson junction. This supercurrent suppression at zero field can be explained by taking the junction to be a π-junction caused by the d-wave symmetry of high-T
c oxide superconductors.
Optoelectronic Parametric Amplification in a Microstrip Ring Resonator on GaAs Substrate
Authors: Lee Jong-Chul , Yeh Chun-Liang , Ho Chien H. , Taylor Henry F. , Mark H. Weichold Mark H. Weichold , Kai Chang Kai Chang
Published: October 2002

Nonlinear interaction between an optically modulated RF input and a microwave LO (local oscillator) in a nonlinear microstrip ring resonator on a semi-insulating GaAs (gallium arsenide) substrate is investigated. When the capacitive reactance of the detector is modulated, a parametric amplification effect of the mixer occurs. In this device structure, a parametric amplification gain of 10 dB without applied bias in the RF signal is obtained. This microwave optoelectronic mixer can be used in fiber-optic communication links.
Fracto-Luminescence of Rare Earth Element-Doped Hexacelsian (BaAl2Si2O8)
Authors: Ishihara Tsuguo , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: October 2002

Luminescence induced by fracture has been observed in rare earth element-doped hexacelsian ( BaAl2Si2O8). The color of the luminescence varies depending on the kinds of doped rare earth element. Eu2+-doped hexacelsian exhibits a luminescence of blue or green color. Sm2+- and Sm3+-doped hexacelsians exhibit a luminescence of red color. The color of luminescence agrees with the emission wavelength in each fluorescence spectrum. It is inferred that the origin of the luminescence is the electronic transition of rare earth ions excited by photons emitted due to fracture of hexacelsian.
Silicon Nitride Thin Films Young's Modulus Determination by an Optical Non Destructive Method
Authors: Buchaillot Lionel , Farnault Etienne , Fujita Moussa Hoummady
Published: October 2002

The purpose of our study is to determine the Young's modulus of silicon nitride ( Si3N4) thin films. With respect to the experimental material, we use commercially available atomic force microscopy (AFM) microcantilevers. The novelty lies in the procedure used to compare and therefore to validate the experimental results. First, the fundamental mode of Si3N4 thin film microcantilevers is detected by means of the optical beam deflection (OBD) method. The resulting resonant frequency is subsequently introduced into the mechanical theoretical model to extract the value of the Young's modulus. A numerical modal analysis is performed to validate the experimental results using the same approach as that of the experiment. Finally, the Young's modulus obtained in this study is compared with those of other studies. The outcome shows that we have obtained a reliable protocol for Young's modulus estimation.
Pulsed Laser Deposition of Corrosion-Resistant Iron Thin Films
Authors: Okoshi Masayuki , Miyake Mitsugu Hanabusa
Published: October 2002

Dense iron thin films with no distinct columnar structure were pulsed laser deposited on Si(100) and quartz, using an ArF laser or a Nd:YAG laser ( 1.064 µm and 532 nm). The deposited films showed no signs of corrosion after exposure to air or immersion in NaCl aqueous solution for many days. The size and density of droplets present in the films decreased with decreasing laser wavelength. Magnetic field application exacerbated the droplet problem.
Epitaxial Growth of BaTiO3 Optical Thin Films by Pulsed KrF Laser Deposition and in situ Pulsed Laser Annealing
Authors: Ito Atsushi , Akihiko Machida Akihiko Machida , Minoru Obara Minoru Obara
Published: October 2002

A simple, hybrid process of pulsed KrF laser deposition (PLD) with in situ pulsed laser annealing has been demonstrated. By this method, epitaxial BaTiO3 optical thin (relatively thick) films with a thickness of up to 2 µ m were successfully fabricated on a MgO substrate for the first time. By in situ pulsed KrF excimer laser irradiation of the surface of the growing film, i.e., in situ laser annealing, good smoothness of the film surface and annealing of the film were achieved, allowing the thick film fabrication. The substrate temperature for the fabrication of epitaxial BaTiO3 films was also reduced to 650° C by incorporating the in situ pulsed laser annealing. Refractive indices of the films were measured to be about 2.30–2.12, which is higher than for films without in situ laser annealing.
Non-Optical Shear-Force Detection for Scanning Near-Field Optical Microscope
Authors: Hiroharu Tamaru Hiroharu Tamaru , Kenjiro Miyano Kenjiro Miyano
Published: October 2002

A non-optical shear-force detection method for use with a scanning near-field optical microscope (SNOM) is proposed. Electrodes on a piezoelectric bimorph are designed so that one part is used for vibrating the scanning probe and the other for detecting the vibration. This provides a very compact actuator-detector pair without any need for optical alignment. Comparison with conventional laser detection shows good correlation for a probe approach curve. A simple method of analyzing the lock-in detected signal for quick and convenient examination of the resonance of the probe is demonstrated.
Observation of Ellipsometric Oscillations when Depositing SiOx Film on Si(100) Substrate Using an Electron Beam Deposition Method
Authors: Yoshioka Yoshifumi , Hashimoto Toyoyuki , Hisamitsu Mamoru , Fumihiko Ohtani Fumihiko Ohtani , Tamio Yoshida Tamio Yoshida
Published: October 2002

We have observed ellipsometric oscillations when depositing SiO

x

film on Si(100) substrate using an electron beam deposition method. A period of these oscillations is calculated to be 5.3 Å thick. From an investigation using a rough surface model in ellipsometry, it is considered that this SiO

x

film is deposited layer-by-layer. This ellipsometry oscillation, first reported in this letter, is applicable to noncrystalline films in which reflection high-energy electron diffraction (RHEED) oscillations are ineffective.
Electron Localization due to Symmetry Breaking in Nonlinear Coupled-Quantum Systems
Authors: Tsukada Noriaki , Gotoda Mitsunobu , Isu Toshiro , Nunoshita Masahiro , Nishino Taneo
Published: October 2002

The effects of nonlinear coupling due to on-site nonlinearlity (Coulomb-charging potential) on dynamic behaviors in coupled-quantum systems are investigated for a number of coupled dots N of 3–17 with a circular-chain configuration. For the initial condition that all dots have the same electron occupation probability, a small initial fluctuation in the electron population causes symmetry-breaking instability of the electron distribution in the coupled-quantum system when the Coulomb-charging potential exceeds a certain threshold value. The threshold value is maximum at N=3 (2.25 times larger than that at N=2) and gradually decreases as the number of coupled dots increases.
High-Pressure Synthesis of AlSr2Ho1-xCaxCu2O7
Authors: Akira Ono Akira Ono
Published: October 2002

The Al-1212 cuprates, AlSr2Ho1-
x

Ca

x

Cu2O7, are prepared at 2 GPa to determine the critical value of x required for the appearance of superconductivity. The Al-1212 cuprates exhibit superconductivity below 18–30 K. Energy dispersive X-ray (EDX) analysis reveals that the critical value of x is approximately 0.56. This value is close to the optimum x value which gave the maximum superconducting transition temperature (T
c) of the Ga-1212 cuprate studied previously. The very high critical value suggests a high concentration of localized holes.
Strong Exciton Absorption Peak Enhancement without Redshift of Absorption Edge in Al 0.3Ga 0.7As/GaAs Five-Step Asymmetric Coupled Quantum Well with Modified Potential
Authors: Hao Feng Hao Feng , Masaki Sugiyama Masaki Sugiyama , Jia-Pang Pang Jia-Pang Pang , Kunio Tada Kunio Tada , Yoshiaki Nakano Yoshiaki Nakano
Published: October 2002

Strong enhancement of exciton absorption peaks at low applied voltage without redshift of the absorption edge, which is attributed to e1hh2 and e2hh1 transitions, was observed at room temperature in a structure composed of five-step asymmetric coupled quantum well (FACQW). The measurement results agree well with our numerical analysis results.
Observation of Laser Oscillation from CaGa 2S 4:Eu 2+
Authors: Seishi Iida Seishi Iida , Tamao Matsumoto Tamao Matsumoto , Nazim T. Mamedov Nazim T. Mamedov , Gyejong An Gyejong An , Yosuke Maruyama Yosuke Maruyama , Ayaz I. Bairamov Ayaz I. Bairamov , B. G. Tagiev B. G. Tagiev , O. B. Tagiev O. B. Tagiev , R. B. Dzhabbarov R. B. Dzhabbarov
Published: October 2002

The first observation of laser oscillation from a single crystal of CaGa2S4:Eu2+ (1 at%) is described in this report. A liquid nitrogen cooled thin platelet (0.8 mm thick), whose one flat surface was coated with aluminum to increase the reflectivity, was excited from the other uncoated side with a pulsed dye laser beam having a photon energy of around 2.48 eV. When the input power density exceeded a threshold value of ∼10 MW/cm2, a directional beam having a sharp spectral line at around 2.19 eV emerged from the sample. This laser was found to have interesting wavelength tunability extending to ∼200 Å, possibly related to the broad gain spectrum of Eu2+ emission in this material.
Second-Order Optical Nonlinearity in Electrically Poled Silicate Glass Containing Ga2O3
Authors: Miyata Masaaki , Nasu Hiroyuki , Mito Akihiro , Tadanori Hashimoto Tadanori Hashimoto , Kanichi Kamiya Kanichi Kamiya
Published: October 2002

Second-harmonic generation (SHG) was observed in silicate glass containing Ga2O3 after electrical poling treatment. The SHG intensity was strongest at the poling temperature of 250° C and for the glass compoition of 7.5Li2O·7.5Cs2O·25Ga2O3·60SiO2 (mol%). The second-order nonlinear coefficient d
33 was as large as ∼13% of d
22 for LiNbO3.
Preparation of CuGaS 2/ZnS Structures on GaAs(100) Substrate by Pulsed Excimer-Laser Deposition
Authors: Hisao Uchiki Hisao Uchiki , Masayoshi Yamaguchi Masayoshi Yamaguchi
Published: October 2002

C-axis-oriented CuGaS2 layers were prepared on ZnS/GaAs(100) substrates by KrF excimer laser deposition. The influence of substrate temperature and laser fluence on layer characteristics was studied. Relatively smooth CuGaS2 layers with a surface roughness of about 30 nm were obtained under optimized preparation conditions.
Selective Self-Formation of InAs Quantum Dots on Strained InGaAs Layers by Molecular Beam Epitaxy
Authors: Yamaguchi Koichi , Eiji Waki Eiji Waki , Hisashi Hasegawa Hisashi Hasegawa
Published: October 2002

InAs was grown on a strained InGaAs/GaAs(001) layer by molecular beam epitaxy. The critical thickness and the dot structure of the InAs were investigated as a function of the thickness of the InGaAs base layer. The critical thickness of the InAs layer increased with decreasing residual strain of the InGaAs surface. Chains of self-formed InAs dots were partially observed along the [110] direction. This selective self-formation of InAs dots was caused by a strain distribution and an anisotropy of the residual strain on the InGaAs surface.
Measurement of Carbon Atom Density in High Density Plasma Process
Authors: Haruhiko Ito Haruhiko Ito , Masanobu Ikeda Masanobu Ikeda , Masafumi Ito Masafumi Ito , Masaru Hori Masaru Hori , Takashi Takeo Takashi Takeo , Hajime Hattori Hajime Hattori , Toshio Goto Toshio Goto
Published: October 2002

Carbon atom densities in an inductively coupled radio frequency (13.56 MHz) CO and CO and H2 mixed plasmas were successfully measured for the first time using ultra-violet absorption spectroscopy (UVAS) with a carbon hollow cathode lamp. This method, developed for monitoring carbon atoms in-situ in the plasmas, is very useful for the investigation of etching and chemical vapor deposition (CVD) processes containing carbon atoms and the sputtering system employing a carbon target.
Control of the In-Plane Orientation in Dye-Containing Langmuir-Blodgett Films by a New Version of the Rotating-Disk Method
Authors: Ikegami Keiichi , Jego Carole , Mingotaud Christophe , Delhaés Pierre
Published: October 2002

The “rotating-disk method” (Mingotaud et al.., 1995) is a powerful technique for obtaining Langmuir-Blodgett (LB) films with controlled in-plane organization. However, the efficiency of this method depends highly on the materials employed and could be reduced for some compounds. In this letter, we propose a two-disk version of the rotating-disk method to control the in-plane organization in LB films more efficiently and more universally. Furthermore, the observed phenomenon is well described by a simple model of the orientation mechanism which is also proposed in this letter.
UV Laser Irradiation Effects on Frequency of Surface Acoustic Wave (SAW) Filters Coated with Titanium Oxide Films
Authors: Ichikawa Yo , Setsune Kentaro , Syun-ichiro Kawashima Syun-ichiro Kawashima , Koichi Kugimiya Koichi Kugimiya
Published: October 2002

Effects of ultraviolet (UV) light irradiation on the frequency of surface acoustic wave (SAW) filters coated with amorphous Ti–O thin films have been investigated by use of a pulsed KrF excimer laser. The frequency was abruptly changed by the irradiation. From the experimental results, it is concluded that the elastic properties of the Ti–O films are improved by the UV laser irradiation, and the frequency shift is dependent on a change in the velocity of SAWs propagating in the Ti–O film.
Barrier Properties for Oxygen Diffusion in a TaSiN Layer
Authors: Hara Tohru , Tanaka Masaru , Sakiyama Keizo , Onishi Shigeo , Ishihara Kazuya , Kudo Jun
Published: October 2002

Annealing in O2 at temperatures above 650° C is required for a thin ferroelectric capacitor. Reduction of the leakage current and an increase of capacitance can be attained in the charge storage capacitor through this annealing. A stacked structure capacitor cell must be practically employed in metal oxide semiconductor large scale integrated circuits (MOSLSI). In this capacitor cell with a conventional Pt/TiN/poly-Si lower electrode, however, O2 annealing can not be attained at high temperature because peeling of the TiN barrier layer and the formation of a thin oxide layer at the surface of poly-Si occur. An noncrystalline TaSiN layer has been studied with respect to the barrier effect for oxygen diffusion used in the barrier layer of the lower electrode. The penetration depth of oxygen diffusion decreases markedly with increasing Si composition in a TaSiN layer and reaches 20 nm deep in a Ta.22Si.35N.43 layer. However, the resistivity increases with this increase. A good diffusion barrier layer with low sheet resistance is attained in a Ta.50Si.16N.34 layer. Penetration depth below 40 nm is obtained in a slightly Si-rich Ta.36Si.27N.37 layer for O2 annealing at 850° C.
Spatially Resolved Detection of Electroluminescence from Lateral p-n Junctions on GaAs (111)A Patterned Substrates Using a Near-Field Scanning Optical Microscope
Authors: Saito Nobuo , Sato Fumio , Takizawa Kuniharu , Kusano Jun-ichi , Okumura Hideyo , Aida Tahito , Saiki Toshiharu , Ohtsu Motoichi
Published: October 2002

Lateral p-n junctions on GaAs (111)A patterned substrates are characterized through the spatially resolved detection of light emission by current injection using a collection-mode near-field scanning optical microscope. The junctions are one-step grown at the upper and the lower end of the slope, taking advantage of the amphoteric nature of Si in GaAs. Although the width of the transition region determined from spatially resolved photoluminescence measurements is much wider in the lower junction than in the upper one, the broadness of the junction, which is observed for the first time owing to the high resolution of the detection system, is the same for both junctions.
Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy
Authors: Usui Akira , Sunakawa Haruo , Sakai Akira , Yamaguchi A. Atsushi
Published: October 2002

Thick GaN layers were grown by hydride vapor phase epitaxy (HVPE) with the aim of using these layers as a homoepitaxial substrate to improve device quality of laser diodes or light emitting diodes. HVPE is very useful for thick layer growth since the growth rate can reach from several ten up to one hundred micron per hour. In this experiment, the growth began as selective growth through openings formed in a SiO2 mask. Facets consisting of {1101} planes were formed in the early stage and a continuous film developed from the coalescence of these facets on the SiO2 mask. As a result, GaN layers with a dislocation density as low as 6×107 cm-2 were grown on 2-inch-diameter sapphire wafers. These GaN layers were crack-free and had mirror-like surface.
Single-Crystalline ZnO Films Grown on (0001)Al2O3 Substrate by Electron Cyclotron Resonance-Assisted Molecular Beam Epitaxy Technique
Authors: Kang Hee-Bog , Nakamura Kiyoshi , Kenji Yoshida Kenji Yoshida , Kazuo Ishikawa Kazuo Ishikawa
Published: October 2002

High quality epitaxial ZnO films were grown on c-plane sapphire substrates at low temperature using the electron cyclotron resonance-assisted molecular beam epitaxy (ECR-assisted MBE) technique, in which zinc vapor provided by a Knudsen cell reacted with oxygen activated in an ECR source on the surface of sapphire substrate. The crystal structure and the surface morphology of the films were investigated. It was confirmed that the ECR-assisted MBE technique was capable of growing high quality epitaxial ZnO films on c-plane sapphire substrates at low temperatures in comparison with CVD or RF sputtering deposition. Furthermore, the FWHM of an X-ray rocking curve of the (0002) peak for a 0.33 µ m-thick ZnO film grown epitaxially at the substrate temperature of 275° C and the oxygen pressure of 2×10-4 Torr was as narrow as 0.58°.
Effects of Dissolved Oxygen on Anodic Etching of n-Type GaN Films Using a Sodium Hydroxide Electrolyte
Authors: Mitsugu Ohkubo Mitsugu Ohkubo
Published: October 2002

Anodic etching, of high quality GaN films grown by metalorganic vapor phase deposition (MOCVD) on a sapphire substrate using a sodium hydroxide (NaOH) electrolyte is reported on. Factors such as the concentration of dissolved oxygen in the NaOH electrolyte affecting the GaN surface are discussed. It is found that the reduction of the concentration of dissolved oxygen in the NaOH electrolyte accelerates the rate of anodic etching of GaN films. The effect of decreasing the concentration of dissolved oxygen in the electrolyte is to reduce the amount of gallium hydroxide formed on the GaN surface. It seems that the concentration of dissolved oxygen in the NaOH electrolyte plays an important role in the anodic etching of n-GaN films.
Gated Volcano-Shaped Field Emitters with Sharp Polycrystalline-Silicon Tips
Authors: Sawada Kazuaki , Suzuki Katsumi , Jayatissa Ahalapitiya H. , Yoshinori Hatanaka Yoshinori Hatanaka , Takao Ando Takao Ando
Published: October 2002

Fabrication of a gated volcano-shaped polycrystalline silicon emitter on a silicon substrate has been studied, and characteristics of this emitter are discussed based on experimental bindings. A new fabrication process is proposed, which uses extended polycrystalline silicon film beneath the SiO2 mask during plasma chemical vapor phase deposition. The advantages of this method are that it produces a sharp emitter tip and reduces the distance between the emitter tip and the gate. It was found that electron emission could be observed at a gate bias as low as 30 V.
Oxynitride Prepared by Liquid Phase Deposition
Authors: Lee Ming Kwei , Bo Hsiung Lei Bo Hsiung Lei , Chung Hsing Lin Chung Hsing Lin
Published: October 2002

Using an aqueous solution of ammonia hydroxide aqua, hydrosilicofluoric acid and boric acid, an oxynitride film can be obtained. Using such a liquid phase deposition method, the growth rate and the refractive index increase with the mole concentration of ammonia hydroxide aqua. After thermal anealing in nitrogen ambient the thickness decreases but the refractive index increases. This distribution of nitrogen atoms accumulate at the interface of oxynitride and silicon. A model is proposed to explain it.
Simulation of Transient Enhanced Diffusion of Boron Induced by Silicon Self-Implantation
Authors: Masashi Uematsu Masashi Uematsu
Published: October 2002

The time and dose dependence of boron transient enhanced diffusion (TED) induced by silicon self-implantation has been simulated taking into account the time evolution of self-interstitial clusters. The kinetics of cluster dissolution and growth are combined with the kick-out mechanism for boron diffusion, and the decrease in the cluster evolution rate with time is taken into account. Using a unified set of parameters, the simulation explains some complex characteristics of TED; that is, the enhancement is independent of the implant dose at short annealing times, while it increases with increasing implant dose after longer annealing times.
Atomic Force Microscope Observation of the Change in Shape and Subsequent Disappearance of “Crystal-Originated Particles” after Hydrogen-Atmosphere Thermal Annealing
Authors: Yanase Yoshio , Nishihata Hideki , Ochiai Takashi , Tsuya Hideki
Published: October 2002

The change in shape and the disappearance of “crystal-originated particles (COPs)” on silicon (111) and (001) surfaces after high-temperature annealing in hydrogen (H2) atmosphere were observed using an atomic force microscope (AFM). It was found that after a very short anneal at 1000°C in H2 atmosphere, the COP width across the wafer surface increases and its depth into the wafer bulk becomes more shallow. Also, as the H2 annealing temperature increases, the time taken for complete COP disappearance decreased. The process of the change in shape and the subsequent disappearance of COPs on silicon (111) and (001) surfaces after H2 annealing was characterized and discussed in terms of the etching effect and reconstruction of silicon atoms.
Mössbauer Study of Magnetic Properties and Structure of Amorphous Fe–(Co, Cr)–Zr Alloys
Authors: Huang Zhigao Huang Zhigao
Published: October 2002

Mössbauer spectroscopy was used to study the effects of composition, temperature, hydrogenation, external magnetic field on series of amorphous Fe90-xCoxZr10(x=4, 10, ..., 70) and Fe90-yCryZr10(y=0, 4, 7, 13, 16, 20) alloys. Magnetic anisotropy and moment distributions in terms of an expansion in spherical harmonies were analyzed. The results reveal the following facts: (i) The hyperfine field distributionsP(Hhf)–Hhfof a- Fe90-xCoxZr10(x=4, 10, 20) and Fe90-yCryZr10(y=0, 4, 7, 13, 16) comprise two or three Gaussian distributions, the low-field and high-field spin fractions obtained from the fitting ofP(Hhf)–Hhfcurve are changed by Co(Cr) content, temperature, applied magnetic field and hydrogenation. (ii) Anomalous behaviors are found in Co(Cr)-poor Fe–(Co, Cr)–Zr alloys, which means the existence of Invar effect and spin-grass-like behavior. (iii) Hydrogenation gives rise to the drastic changes of the hyperfine parameters, which can mainly be associated with the volume and hybridization effect. (iv) The moment distributions of a- Fe90-xCoxZr10(x=4, 10, 20, 30, 40) are preferentially in the direction of the film length. A 90°-type magnetic coupling between spin-clusters in 3DFM and in FSC may exist in Co(Cr)-poor Fe–(Co, Cr)–Zr alloys. A “3DFM+FS+FSC” model containing density inhomogeneity provides a rather satisfactory explanation.
Biological Behavior of Dextran-Iron Oxide Magnetic Fluid Injected Intravenously in Rats
Authors: Hasegawa Masakatsu , Hanaichi Takamasa , Shoji Hirokazu , Kawaguchi Takeshi , Maruno Shigeo
Published: October 2002

Dextran-magnetic iron oxide complex (CMDM) consisting of carboxymethyl dextran and a magnetite core has been synthesized. The physical and biological properties were compared with those of the conventional dextran-magnetite complex (ATDM). The CMDM exhibits a super-paramagnetic property, has high stability and low toxicity. The uptake and metabolic behavior of CMDM in live rats after intravenous (iv) administration were studied using pulsed nuclear magnetic resonance, optical microscopy and transmission electron microscopy. The ultrafine particles of CMDM were clearly observed in the lysosomes of Kupffer cells in the liver and of macrophages in the spleen. The CMDM accumulated in the lysosomes was found to disappear within two weeks after the iv-injection. The results obtained in this work suggest that CMDM is appropriate for use as a contrast agent for magnetic resonance imaging (MRI).
New Insight into the Degradation Mechanism of Nitride Spacer with Different Post-Oxide in Submicron LDD n-MOSFET's
Authors: Yih C. M. , Wang C. L. , Chung Steve S. , Wu C. C. , Tan W. , Wu H. J. , Pi S. , Huang Daniel
Published: October 2002

In this paper, the hot carrier degradation mechanisms in lightly-doped drain (LDD) n-MOS devices with silicon nitride spacer have been investigated. A low temperature chemical vapor deposited (CVD) SiO2 oxide is used as a post-oxide between source/drain surface and the nitride spacer. The gated-diode measurement in combination with the gate-induced drain leakage (GIDL) current measurement techniques have been used to analyze the stress-induced interface state and oxide charges. For the first time, it was found that the oxide charge but not the interface state generation in the post oxide will dominate the device drain current degradation. Moreover, the CVD post oxide with N2 annealing has been proposed which is able to effectively suppress the generation of oxide charges and significantly improve the device hot carrier reliability. The scaling of gate oxide thickness and the optimization of source/drain junction to improve the device reliability are also demonstrated.
Short Channel Effects in N- and P-Channel Polycrystalline Silicon Thin Film Transistors with Very Thin Electron Cyclotron Resonance N2O-Plasma Gate Dielectric
Authors: Lee Jin-Woo , Lee Nae-In , Han Chul-Hi
Published: October 2002

To suppress short-channel effects in polysilicon thin film transistors, very thin electron cyclotron resonance (ECR) N2O-plasma gate oxide is investigated experimentally. ECR N2O-plasma oxidation incorporates nitrogen atoms at the interface and forms strong Si≡N bonds. With the ECR N2O-plasma oxide of 12 nm thickness, short-channel effects can be almost eliminated for n-channel (p-channel) thin film transistors of 3 µm (1 µm) gate length. It is inferred that reduction of defects by N2O-plasma passivation and strong Si≡N bonds lead to good immunity to impact ionization, resulting in the suppression of short-channel effects.
Dry Thermal Oxidation of Polycrystalline and Amorphous Silicon Films for Application to Thin Film Transistors
Authors: Miyasaka Mitsutoshi , Itoh Wataru , Ohshima Hiroyuki , Shimoda Tatsuya
Published: October 2002

Dry thermal oxidation of polycrystalline silicon (p-Si) and amorphous silicon (a-Si) has been studied. An oxidation temperature of 1070°C is a break point, at which the oxidation time of one atomic layer is nearly equal to the stress relaxation time. Below the break point temperature, oxidation stress is not relaxed at the silicon-oxide interface, because the stress relaxation time is longer than the oxidation time of one atomic layer. The high oxidation stress, together with the presence of grains and grain-boundaries, makes the interface rough, resulting in poor electrical properties in p-Si thin film transistors (TFTs). It is, therefore, important for fabricating good TFTs that p-Si or a-Si films are oxidized under conditions such that the oxidation time of one atomic layer is longer than the stress relaxation time to relax the oxidation stress at the interface.
Amorphous Silicon Avalanche Photodiode Films Using a Functionally Graded Superlattice Structure
Authors: Sawada Kazuaki , Okumura Yoshihiro , Hatanaka Yoshinori , Ando Takao
Published: October 2002

The photocurrent multiplication due to impact ionization was observed in an a-Si:H/a-SiC:H staircase photodiode. In the staircase photodiode with one band offset, the photocurrent was doubled and was saturated. It was confirmed that almost all the electrons multiplied after they crossed the band offset. On the staircase photodiode with 3 band offsets, a saturation multiplication gain of about 6 was obtained. The gamma values of the photocurrent characteristics were 1.0, indicating that no excess carriers entered from the electrode and no interband tunneling affected the photoinduced current. These results suggested that the impact-ionization at each conduction band step due to the conduction-band discontinuity could be the dominant mechanism of the photocurrent multiplication.
Negative-Resistance Effects in Light-Emitting Porous Silicon Diodes
Authors: Ueno Koki , Koshida Nobuyoshi
Published: October 2002

Definite negative-resistance (NR) effects in electroluminescence(EL)-emissive porous silicon (PS) diodes have been investigated in relation to the EL characteristics. The PS diode is composed of a semitransparent thin Au film, a relatively thin PS layer, a n+- or p-type Si substrate and an ohmic back contact. When the forward bias voltage is applied to the diode, a reversible NR behavior is observed in the current–voltage (I–V) characteristics at room temperature. At a low temperature of 10 K, the peak-to-valley current ratio in the n+-type substrate case extends to about 104. It is shown that the EL emission is switched on at the onset of the NR effect. For the p-type substrate diode, the NR effects can be activated by photoillumination. The mechanism of the observed NR effects is also discussed from the viewpoint of electron injection into the silicon nanocrystallites in PS. The NR effects can be regarded as one of the field-induced functions of PS as a quantum-sized crystalline system.
Electrical Characteristics of Neuron Oscillation Circuits Composed of MOSFETs and Complementary Unijunction Transistors
Authors: Sung-min Yoon Sung-min Yoon , Yuji Kurita Yuji Kurita , Eisuke Tokumitsu Eisuke Tokumitsu , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

A pulse frequency modulation (PFM) type neuron circuit composed of a metal-oxide-semiconductor field effect transistor (MOSFET) and a complementary unijunction transistor (CUJT) was fabricated on a silicon-on-insulator (SOI) structure as an approach to an adaptive learning neuron circuit using a metal-ferroelectric-semiconductor field effect transistor (MFSFET). The output pulse interval was controlled by changing the pulse duty ratio of input pulse signals as well as the magnitude of the DC input voltage. These results demonstrate that the electrical properties of MOSFET neuron circuits are good enough for future neural networks, that can be expected to be realized by replacing the MOSFET with an MFSFET. A new circuit using a complementary MOS (CMOS) Schmitt-trigger configuration is also proposed for improving output pulse amplitude.
Effect of Bottom Polysilicon Doping on the Reliability of Interpoly Oxide Grown Using Electron Cyclotron Resonance N2O-Plasma
Authors: Lee Nae-In , Lee Jin-Woo , Hur Sung-Hoi , Kim Hyoung-Sub , Han Chul-Hi
Published: October 2002

The Effects of the bottom polysilicon doping on the reliability of polyoxides grown using electron cyclotron resonance (ECR) N2O-plasma have been investigated for the interpoly dielectrics (IPDs) of nonvolatile memories (NVMs). In situ doped polysilicon films have a smooth surface. ECR N2O-plasma polyoxide on in situ doped polysilicon has a lower leakage current and a higher breakdown field, furthermore, a lower electron trapping rate and a larger charge-to-breakdown (Q
bd) up to 10 C/cm2, which is comparable to the electrical properties of ONO IPD. This is mainly attributed not only to a nitrogen-rich layer with strong Si–N bonds but also to a smooth interface. We conclude that ECR N2O-plasma polyoxide on in situ doped polysilicon is a good candidate for an interpoly dielectric of future high density NVMs.
Directional Plasma CVD Technology for Sub-quarter-micron Feature Size Multilevel Interconnections
Authors: Kudoh Yutaka , Homma Yoshio , Sakuma Noriyuki , Furusawa Takeshi , Kusukawa Kikuo
Published: October 2002

A new plasma chemical vaper deposition (CVD) technology, which provides outstanding film step coverage for sub-quarter-micron, high-aspect-ratio steps on ultralarge semiconductor integrated (ULSI) device surfaces, has been developed. The technology employs a bias plasma CVD deposition system with wide-gap electrodes and reaction gases of triethoxysilane (TRIES) and oxygen. This technology improves the step coverage of SiO2 films by reducing the lateral ledge to less than 60% of that associated with conventional plasma CVD. It also improves the film quality of the SiO2 deposited on the step sidewalls in reducing the sidewall etching rate to less than 50% of that of conventional films. This technology has been applied to an interlevel dielectric (ILD) process in conjunction with organic spin-on-glass (SOG), and the ILD parasitic capacitance was reduced to about 70% of that in conventional plasma CVD. This technology is very promising for application to 0.2 µm feature size ULSI interconnections.
Effects of Reaction Product During Hydrogenation of Si Surfaces in HF Solution
Authors: Sugita Yoshihiro , Watanabe Satoru
Published: October 2002

The reaction between the H-terminated Si surfaces and H2SiF6 solution, which is a reaction product of the dissolving SiO2 in the HF solution, was examined. The H2SiF6 solution selectively oxidized the mono-hydride on Si and degraded the hydrophobicity of the surface, while the di-hydride on Si remained stable in the solution. These results explained the crystal orientation dependence of the oxide removal from the Si surface.
Characterization of Hydrogen in Epitaxial Silicon Films Grown at Very Low Temperatures
Authors: Abe Katsuya , Watahiki Tatsuro , Yamada Akira , Konagai Makoto
Published: October 2002

Experimental and theoretical analyses of hydrogen atoms incorporated in epitaxial silicon films grown at very low temperatures were investigated using a high resolution X-ray diffractometer (HRXRD) and an ab-initio total energy calculation. We found that the lattice constant of the epitaxial films was expanded by the H atoms and this lattice expansion occurred only in a direction normal to the surface. We proposed the Si–H–Si configuration as a model to explain the lattice expansion phenomenon. The results of the calculation supported this model and also suggested that the microscopic stress was introduced by the H atom in the configuration. In B-doped epitaxial Si films, the B atoms were 100% neutralized by the H atoms and activated by thermal annealing. We increased the growth temperature to overcome these H related problems and succeeded in controlling the H incorporation. The B-doped Si film with a hole concentration of 1.7×1019 cm-3 was obtained at a growth temperature of 240°C.
Source-Bias Dependent Charge Accumulation in P+-Poly Gate SOI Dynamic Random Access Memory Cell Transistors
Authors: Sim Jai-hoon , Kim Kinam
Published: October 2002

In this paper, we report the dynamic data retention problems caused by the transient leakage current in a cell transistor during the bit-line pull down operation in p+-poly gate fully depleted silicon-on-insulator (FD-SOI) dynamic random access memories (DRAMs) due to the source-induced charge accumulation (SICA) effect in the silicon thin film. Due to the inherent floating body effect in the FD-SOI transistor, charge accumulation in the silicon thin film becomes inevitable when the gate-to-source voltage (V
GS) is smaller than the flat-band voltage (V
FB). In order to eliminate the transient leakage current problem in p+-poly gate FD-SOI cell transistor, the ground-precharged bit-line (GPB) sensing method is introduced.
New Measurement Technique for Sub-Bandgap Impact Ionization Current by Transient Characteristics of Partially Depleted SOI MOSFETs
Authors: Takuya Saraya Takuya Saraya , Makoto Takamiya Makoto Takamiya , Tran Ngoc Duyet Tran Ngoc Duyet , Toshiro Hiramoto Toshiro Hiramoto
Published: October 2002

We have developed a novel, sensitive measurement technique for the sub-bandgap impact ionization current in scaled metal-oxide-semiconductor field effect transistors (MOSFETs). In this technique, partially depleted silicon on insulator MOSFETs is utilized where the floating body potential is gradually charged by the impact ionization current. The transient increase of the body potential causes a decrease in the threshold voltage due to the body effect, resulting in a transient increase in the drain current. The impact ionization current is derived from the transient increase in the body potential. The derived impact ionization current is in good agreement with the direct current measurement. Furthermore, the new measurement technique is very sensitive even in the sub-bandgap region and measurements of less than 50 fA are demonstrated.
Evaluation of Electron Trap Levels in SOI Buried Oxides by Transient Photocurrent Spectroscopy
Authors: Miura Yoshinao , Hamada Kouichi , Kitano Tomohisa , Ogura Atsushi
Published: October 2002

An electron trap density of 2×1015 cm-3 in a buried oxide of silicon-on-insulator structure is detected by transient photocurrent spectroscopy. Through the two-step photodepopulation method, the distribution of electron trap level was found to have a peak at 2.3 eV below the oxide conduction band edge. The capture cross section of 8.8×10-14 cm2 meant that the electron traps are positively charged centers. Flatband shift measurement indicates that pre-existing positive charges in the oxide are compensated for by photoelectron injection. These results suggest that the pre-existing positive charges and the electron traps have an identical origin.
Mobility Enhancement of SOI MOSFETs due to Subband Modulation in Ultrathin SOI Films
Authors: Takagi Shin-ichi , Koga Junji , Toriumi Akira
Published: October 2002

We propose that silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistors (MOSFETs) with SOI films thinner than the inversion layer of the bulk MOSFETs can provide higher inversion-layer mobility than the bulk Si MOSFETs, because of the significant modulation of the subband structure due to the size effect of the ultrathin SOI films. In order to examine the effectiveness of this device structure on the mobility enhancement, a theoretical calculation of the inversion-layer mobility at room temperature is performed. It is found that the mobility of the SOI MOSFETs with a SOI thickness of around 3 nm can be higher than that of the bulk MOSFETs. This mobility enhancement is attributed to an increase in the occupancy of the 2-fold valleys and the suppression of inter-valley phonon scattering, associated with the energy splitting between the 2-fold and the 4-fold valleys due to the size effect of the SOI films.
Application of Reversed Silicon Wafer Direct Bonding to Thin-Film SOI Power ICs
Authors: Ishiyama Toshihiko , Matsumoto Satoshi , Hiraoka Yasushi , Sakai Tatsuo , Yachi Toshiaki , Yamada Ichiro , Itoh Akio , Arimoto Yoshihiro
Published: October 2002

Reversed silicon wafer direct bonding (RSDB) has been applied to Silicon-on-insulator (SOI) power Integrated Circuits (ICs). The RSDB power metal-oxide-semiconductor field-effect transistor (MOSFET) is superior to the power MOSFET using a conventional SOI substrate. In a RSDB power MOSFET, the threshold voltage is independent of the substrate bias because its gate electrode shields the substrate bias from the channel. Moreover, the parasitic bipolar effect is suppressed. RSDB also has a higher production yield. Two-dimensional device simulation results show how to optimize the device parameters enabling us to maximize the breakdown voltage of the RSDB power MOSFET. The electrical characteristics of nMOSFETs fabricated using RSDB are the same as those of nMOSFETs fabricated using the conventional SOI substrate.
Ultrahigh Electron Mobilities in Si1-xGex/Si/Si1-xGex Heterostructures with Abrupt Interfaces Formed by Solid-Phase Epitaxy
Authors: Sugii Nobuyuki , Nakagawa Kiyokazu , Kimura Yoshinobu , Yamaguchi Shinya , Miyao Masanobu
Published: October 2002

Si1-x
Ge
x
/Si/Si1-x
Ge
x
heterostructures with a flat channel were successfully fabricated by molecular-beam epitaxy combined with solid-phase epitaxy. The solid-phase epitaxial growth completely suppressed Ge segregation between the channel layer and the doped layer. Cross-sectional transmission-electron-microscope images revealed that misfit dislocations were limited to the bottom part of the buffer layer and to the substrate, and that the heterointerfaces were very smooth and flat. The electron mobility for a sample with a graded buffer layer was nearly one order of magnitude higher than without such a layer. Ultrahigh mobility of 8.0×105 cm2V-1s-1 was obtained at 15 K for a sample with a graded buffer layer (x=0.2).
Effects of Segregated Ge on Electrical Properties of SiO2/SiGe Interface
Authors: Chang-Geun Ahn Chang-Geun Ahn , Hee-Sung Kang Hee-Sung Kang , Young-Kyu Kwon Young-Kyu Kwon , Bongkoo Kang Bongkoo Kang
Published: October 2002

The effects of segregated Ge on the electrical properties of the SiO2/SiGe interface are investigated. It is observed that the segregated Ge near the SiO2/SiGe interface, formed during oxidation of the SiGe layer, affects the threshold voltage of a metal-oxide-semiconductor (MOS) structure, and that the flat-band voltage shift increases when the Ge segregation is increased. The densities of the interface states and fixed charges are measured using the capacitance-voltage (C–V) method, and the relationships between these results and the material properties are examined. From the results, the SiO
x
structures are responsible for the increased negative fixed charges near the SiO2/SiGe interface. The mechanism proposed for the generation of negative fixed charges is that the oxygen in the Ge pileup region forms a Si–O–Ge bonding structure initially, and then the weaker Ge-O bond can easily be broken, leaving a Si–O– dangling bond and elemental Ge. The Si–O– dangling bond assumes a negative fixed charge state by trapping an electron.
Dispersion Compensation for a Femtosecond Cr:LiSAF Laser
Authors: Sadao Uemura Sadao Uemura
Published: October 2002

The group delay per length for Cr:LiSAF crystal has been measured, and the result indicates that the refractive index of Cr:LiSAF has a large error. The dispersion of a prism pair is calculated without approximations to be estimated in a large wavelength range. The conditions in which the group delay dispersion and third order dispersion of a femtosecond-Cr:LiSAF-laser cavity are simultaneously zero have been discussed.
Structure and Electrical Properties of Thin Ta2O5 Deposited on Metal Electrodes
Authors: Kishiro Koichi , Inoue Nobuhiko , Chen Shih-Chang , Yoshimaru Masaki
Published: October 2002

The structure and electrical properties of chemical vapor deposition (CVD)-Ta2O5 thin films on Pt, Ru and poly-Si electrode were studied. With 750°C annealing after Ta2O5 deposition, a 12-nm-thick Ta2O5 on Pt and Ru shows a SiO2 equivalent thickness (t
eq) of 0.9 nm. We found that Ta2O5 on Pt and Ru shows (110) and (001) orientation, respectively. There is no interaction between Ta2O5 and these electrodes with 750°C annealing. t
eq on Pt and Ru decreases with annealing temperature increase. On the other hand, Ta2O5 on poly-Si is randomly oriented and its t
eq does not change with annealing temperature increase. The relative dielectric constant of Ta2O5 on Pt and Ru, which is highly oriented with 750°C annealing, is estimated over 50. It is clear that the Ta2O5 electrical properties are strongly related with its crystallinity.
Electrical and Microstructural Analyses on the Au/Ni/Au/Ge/Pd Ohmic Contact to n-InGaAs and n-GaAs
Authors: Kim Il-Ho , Park Sung Ho , Kim Jwayeon , Lee Jong-Min , Lee Tae-Woo , Park Moon Pyung
Published: October 2002

The Au/Ni/Au/Ge/Pd ohmic contact systems on n-InGaAs and n-GaAs were studied and compared. In the contact to n-InGaAs, relatively good ohmic behavior was found even without annealing due to lower barrier height, and a better ohmic contact was obtained by rapid thermal annealing up to 400°C. However, above 425°C it was deteriorated by intermixing and phase reaction of the ohmic metals and InGaAs substrate. The out-diffusion of In and As degraded the ohmic contact due to an increase in barrier height and charge compensation. As for the contact to n-GaAs, non-ohmic behavior was shown before annealing, but significant reduction of the specific contact resistance was made by annealing. In both contacts, non-spiking and planar interfaces were observed even when annealed at 425°C, and surface morphologies were nearly the same as the as-deposited contacts up to 400°C, which showed smooth and shiny surfaces.
Metalorganic Vapor-Phase Epitaxial Growth and Characterization of Cubic AlxGa1-xN Alloy
Authors: Nakadaira Atsushi , Tanaka Hidenao
Published: October 2002

Cubic Al
x
Ga1-x
N alloy films in the range 0≤x≤0.51 were grown on GaAs (100) substrates using low-pressure metalorganic vapor-phase epitaxy. The lattice constants of the alloys, which were estimated from the X-ray diffraction peaks, obeyed Vegard's rule. The optical quality of the alloys was improved by using triethylaluminum as the aluminum precursor. In photoluminescence measurements, Al
x
Ga1-x
N in the range x≤0.42 exhibited strong near band edge emissions, while that with x around 0.5 did not. The peak energy of the photoluminescence depended on the relationship E=3.20+1.85x in the range x≤0.42, while that around x=0.5 was less than that given by this relationship.