bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic Changes in SiO2/Si(111) Interface Structures with Progress of Thermal Oxidation
Authors: Kazuaki Ohishi Kazuaki Ohishi , Takeo Hattori Takeo Hattori
Published: October 2002

Changes in SiO2/Si(111) interface structures during the progress of oxidation through 0.5-nm-thick preoxide were investigated at 600 and 800°C in dry oxygen with a pressure of 133 Pa by measuring oxidation-induced changes in Si 2p photoelectron spectra. The following results are obtained: 1) at 800°C, oxidation reaction occurs monolayer by monolayer at the interface, however, 2) monoatotnic steps exist at the interface in every stage of oxidation.
GaN Core Relaxation Effects and Their Ramifications for P-Type Doping
Authors: S. Strite S. Strite
Published: October 2002

Evidence for the presence of d-electron core relaxation effects in GaN and InN is examined by comparing the physical properties of these materials with those of AlN and the group III arsenides and phosphides. The comparison strongly suggests that d-electron core relaxation effects play an important role in the properties of the III–V nitride semiconductors. Based on these observations, it is proposed that Ca and C be investigated as dopants potentially superior to Mg for p-type doping of GaN.
Spatial Distribution and Its Phase Transition of Densely Contact-Electrified Electrons on a Thin Silicon Oxide
Authors: Sugawara Yasuhiro , Morita Seizo , Fukano Yoshinobu , Uchihashi Takayuki , Okusako Takahiro , Chayahara Ayumi , Yamanishi Yoshiki , Oasa Takahiko
Published: October 2002

We investigated the spatial distribution of densely contact-electrified electrons on a silicon oxide layer in air with a modified AFM. From the observed full width at half-maximum (FWHM) and the peak value, we found that the spatial stable-unstable phase transition occurs. We also found, for the first time, that an unstable state exists around the stable state, and that the boundary of the stable state collapses into the unstable state. We also found that the stable state turns into the unstable state by a spatial phase transition and subsequently into the trapped state.
Flux Pinning in Melt-Grown NdBa2Cu3Oy and SmBa2Cu3Oy Superconductors
Authors: Murakami Masato , Yoo Sang-Im , Higuchi Takamitsu , Sakai Naomichi , Weltz Jürgen , Naoki Koshizuka Naoki Koshizuka , Shoji Tanaka Shoji Tanaka
Published: October 2002

REBa2Cu3O

y

superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm) exhibit relatively low T
c due to the presence of RE-Ba solid solution. We have found that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere. We have also found that critical current densities of these superconductors are higher than those of melt processed YBa2Cu3O

y

with fine Y2BaCuO5 inclusions in a high field region. The irreversibility line was also shifted toward the higher H-T region. We believe that flux pinning in these superconductors is ascribable to a finely distributed RE(Ba1-
x

, RE

x

)2Cu3O

y

phase in a good superconductive matrix.
Direct Spectroscopic Evidence of Bias-Induced Shifts of Semiconductor Band Edges for Metal-Insulator-Semiconductor Diodes
Authors: Kobayashi Hikaru , Yamashita Yoshiyuki , Kenji Namba Kenji Namba , Yoshihiro Nakato Yoshihiro Nakato
Published: October 2002

Direct evidence of the bias-induced shift of semiconductor band-edges has been obtained for the first time from X-ray photoelectron spectroscopic (XPS) measurements under bias. The metal-insulator-semiconductor (MIS) diodes with the about 30-Å-thick platinum layer/about 25-Å-thick silicon oxide layer/n-Si (100) structure are used for the XPS measurements. By applying a forward bias (or reverse bias) to the MIS diodes, the binding energy of the substrate Si(2p) peak with respect to the Pt(4f) peak is decreased (or increased), and is attributed to the upward (or downward) shift of the Si band-edges caused by accumulation of negative charges (or positive-charges) in the surface states.
Surface Diffusion of Bi2Sr2CuO6+xThin Films Grown by Molecular Beam Epitaxy
Authors: Ishibashi Takayuki , Yoshitaka Okada Yoshitaka Okada , Mitsuo Kawabe Mitsuo Kawabe
Published: October 2002

The surface diffusion characteristics ofBi2Sr2CuO6+xthin films grown by molecular beam epitaxy (MBE) on tilted SrTiO3(001) substrates have been investigated by usinginsitureflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The periodic intensity oscillations corresponded to 1/2 unit layer-by-layer growths have been observed for low growth temperatures and high growth rates, while periodic oscillations disappeared with increasing growth temperature and/or decreasing growth rate. The decrease of RHEED oscillation indicates that the growth mode changes, from two dimensional (2-D) nucleation growth to step-flow mode.
Scaling Behavior of YBaCuO/PrBaCuO/YBaCuO Trilayer Josephson Junctions
Authors: Akoh Hiroshi , Sato Hiroshi , Norito Nakamura Norito Nakamura , Susumu Takada Susumu Takada
Published: October 2002

We have fabricated Josephson junctions consisting of all (103)-oriented YBaCuO/PrBaCuO/YBaCuO trilayer films, varying the thickness of the PrBaCuO barrier from 45 to 100 nm and the junction area from 10×10 to 50×50 µm2. A scaling behavior with critical current× normal resistance ( I
c
R
n products) proportional to (critical current density J
c)1/2 is observed for fabricated trilayer junctions. Furthermore, it is found that junctions with trilayer and edge structures reported by other groups also obey this scaling behavior, strongly suggesting that the junction properties can be determined by the lowered value of the order parameter at the interface between the YBaCuO film and barrier layer, due to the proximity effect within the framework of the short-coherence-length effect.
Single-Longitudinal-Mode Operation and Larger Energy Diffusion due to Intracavity Second Harmonic Generation in a Nd:YVO4 Microchip Laser
Authors: Zhou Wang-Long , Takatomo Sasaki Takatomo Sasaki , Sadao Nakai Sadao Nakai
Published: October 2002

We report a method of single-longitudinal-mode operation by using intracavity second harmonic generation in a Nd:YVO4 microchip standing-wave laser under high pump power. The effects of energy diffusion in the laser medium on laser oscillation and mode interval are also discussed.
Kerr Rotation of Quenched High-Temperature-Phase MnBi Film
Authors: Di Guo-Qing , Oikawa Soichi , Iwata Satoshi , Shigeru Tsunashima Shigeru Tsunashima , Susumu Uchiyama Susumu Uchiyama
Published: October 2002

Quenched high-temperature-phase MnBi film was successfully obtained by quenching the low-temperature-phase MnBi film in air. The high-temperature-phase has been found to appear below 300°C, which is different from a previously reported result. Its Kerr rotation and Kerr ellipticity spectra have been measured at room temperature, and are very different from that of the low-temperature-phase MnBi film in both magnitude and spectral structure.
Optical Absorption in Higher Fullerenes: Effects of Symmetry Reduction
Authors: Kikuo Harigaya Kikuo Harigaya
Published: October 2002

Optical absorption spectra of higher fullerenes ( C70 and C76) as well as of C60 are calculated by a tight binding model with a long-range Coulomb interaction. A reasonable parameter set gives calculated spectra which are in overall agreement with those obtained from experiments of C60 and C70 in solutions. The variations of the spectral shape are discussed in relation to the symmetry reduction from C60 and C70 to C76: the optical gap decreases and the spectra exhibit a larger number of small structures in the dependences on the excitation energy.
Observation of Coulomb-Crystal Formation from Carbon Particles Grown in a Methane Plasma
Authors: Yasuaki Hayashi Yasuaki Hayashi , Kunihide Tachibana Kunihide Tachibana
Published: October 2002

A Coulomb crystal was successfully formed as a result of the growth of spherical and monodisperse carbon particles suspended in a methane plasma. The crystal structure was confirmed to be hexagonal from top- and side-view photographs. The particle growth was monitored by Mie-scattering ellipsometry and correlated with the formation process of the Coulomb crystal. The liquid-to-solid phase transition occurred when particle diameter grew to 1.3 µm, and when the Wigner-Seitz radius was about 90 µm.
Influence of Boron Adsorption over Si(111) Surface on Si Molecular Beam Epitaxial Growth Studied by Reflection High-Energy Electron Diffraction
Authors: Kumagai Yoshinao , Mori Ryosuke , Kouichi Ishimoto Kouichi Ishimoto , Fumio Hasegawa Fumio Hasegawa
Published: October 2002

Epitaxial growth of Si on top of a boron-adsorbed Si(111) surface was studied in a molecular beam epitaxy (MBE) system. When the initial boron coverage was more than 1/3 monolayer (ML), reflection high-energy electron diffraction (RHEED) intensity oscillation showed a 4 ML period in the early stage of Si growth as long as surface-segregated boron at the growing surface was more than 1/3 ML, and turned to the normal 2 ML period of oscillation. Periodical change of the full width at half-maximum (FWHM) of the RHEED specular spot confirmed that this is due to two-dimensional island growth of 4 ML height and the coalescence mode of Si.
Relationship between Different Interfacial Phases and Oxygen Solubility in Silicon Melt
Authors: Huang Xinming , Terashima Kazutaka , Koji Izunome Koji Izunome , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

Different interfacial phases formed at the interface between undoped or Sb-doped Si melt and SiO2 were observed, and the relationship between the interfacial phases and oxygen solubility in the Si melts was investigated. A foil-form interfacial phase with composition of about SiO1.8 appeared between the bulk Si melt and SiO2 ampule wall when the Sb concentration in the Si melt was less than 0.5 at%. However, the from of the interfacial phase became dendritic and composition changed to SiO2 when the Sb concentration was in the range from 0.5 to 2.0 at%. The interfacial phase disappeared when the Sb concentration reached about 2.0 at%. Corresponding to the different interfacial phases, the equilibrium oxygen concentrations in the Si melt also changed considerably, i.e., from 2×1018 at/cm3 to about 2×1019 at/cm3.
The Annealing Effects of Excimer-Laser-Produced Large-Grain Poly-Si Thin-Film Transistors
Authors: Do-Hyun Choi Do-Hyun Choi , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

Annealing effects have been studied for thin-film transistors (TFTs) with excimer-laser recrystallized large-grain poly-Si films. Electron field-effect mobility of about 350 cm2/V·s, i.e., much higher than the typical value, can be obtained by simple vacuum anneal. Effects of atomic hydrogen and molecular hydrogen anneals are also identified.
Enhanced Electron Mobility in the Inverted High Electron Mobility Transistor Structure by Two-Step Molecular Beam Epitaxy (MBE) Growth
Authors: Washima Mineo , Mishima Tomoyoshi , Kudo Makoto
Published: October 2002

Electron mobility dependence on molecular beam epitaxy (MBE) growth temperature for the channel layer in inverted high electron mobility transistors (HEMTs) has been investigated. 77 K 2-DEG mobility is increased up to 101200 cm2·V-1·s-1, even with a thin spacer layer (8 nm) by raising the growth temperature to 660° C, after growing the underlying n-AlGaAs:Si at 450° C. Its mobility is 43% higher than that of a continuously grown sample whose channel layer was grown at 450° C. With a thicker spacer layer (25 nm), two-step MBE growth facilitated very high mobility of 165000 cm2·V-1·s-1 at 77 K and 550000 cm2·V-1·s-1 at 10 K.
Simultaneous Switching on Vertically Stacked Josephson Junctions with Very Thin Intermediate Electrode
Authors: Hirotake Yamamori Hirotake Yamamori , Akira Fujimaki Akira Fujimaki , Yoshiaki Takai Yoshiaki Takai , Hisao Hayakawa Hisao Hayakawa
Published: October 2002

We have demonstrated vertically stacked Josephson junctions with very thin superconductors for the intermediate electrode. The gap voltage of a thin film decreases as the thickness decreases, but the decrease of the energy gap does not worsen the quality of the junction. In the double junction, simultaneous switching between the lower and upper junctions is observed. Although simultaneous switching is also observed in the series-connected Josephson junction, we have found some differences between them and have investigated the condition of simultaneous switching in the double junction.
RuO2 Thin Films as Bottom Electrodes for High Dielectric Constant Materials
Authors: Yoshikawa Kohta , Kimura Takafumi , Noshiro Hideyuki , Otani Seigen , Masao Yamada Masao Yamada , Yuji Furumura Yuji Furumura
Published: October 2002

Ruthenium dioxide ( RuO2) thin films are evaluated as a bottom electrode for SrTiO3. It was found that a thin RuO2(50 nm)/Ru(20 nm) layer on Si is quite effective as a barrier layer for both orygen atoms and metals when depositing SrTiO3 at a relatively low temperature of 450° C. To test its suitability for high-temperature processes such as CVD of SrTiO3, the RuO2/Ru electrode on Si was annealed in air at 600° C for 1 hour. Even under this severe condition, the electrode using 100-nm-thick RuO2 was sufficient for preventing oxygen diffusion into Si.
Efficient Field Effect in Heavily Doped Thin-Film Diamond Metal-Insulator-Semiconductor Diode Employing BaTiO3 Insulator Film
Authors: Ariki Takuya , Shikama Shozo , Suzuki Sei , Otsuka Yuzuru , Tetsuro Maki Tetsuro Maki , Takeshi Kobayashi Takeshi Kobayashi
Published: October 2002

Metal-insulator-semiconductor (MIS) structures of heavily doped ( 6–7×1018 cm-3) epitaxial diamond were prepared, which include highly polarizable BaTiO3 insulator films. They were characterized by capacitance-voltage ( C-V) and electron-beam-induced-current (EBIC) measurements. Despite the presence of background boron of an extremely high concentration, an applied voltage of at most 10 V was sufficient to establish the deep-depletion condition at the diamond surface. The observed EBIC image gave a more direct indication of the efficient field effect in our diamond MIS structures.
Observation of Direct Transitions in Silicon Nanocrystallites
Authors: Zhao Xinwei , Schoenfeld Olaf , Kusano Jun-ichi , Yoshinobu Aoyagi Yoshinobu Aoyagi , Takuo Sugano Takuo Sugano
Published: October 2002

Silicon nanocrystallites show intense violet and blue luminescence at room temperature. The luminescence band exhibits separated peaks at a wavelength range from 350 nm to 550 nm under N2 pulse laser excitation. Lifetimes of these emissions can be fitted by double-exponential equations. The two parts of the lifetime, τ1 and τ2, were determined as 100∼300 ps and 600∼800 ps, respectively. All the optical events were finished within 5 ns. This short lifetime is suggested to be caused by an enhancement effect on the oscillator strength of the confined levels in zero-dimensionally confined Si nanocrystallites.
Investigation of Deep Levels and Residual Impurities in Sublimation-Grown SiC Substrates
Authors: Uddin Ashraf , Hiroshi Mitsuhashi Hiroshi Mitsuhashi , Tsutomu Uemoto Tsutomu Uemoto
Published: October 2002

Deep levels and residual impurities in sublimation-grown n-type SiC substrates are investigated. Three electron trap centers at 0.26, 0.35 and 0.72 eV below the conduction band (CB) are observed in 4H-SiC for the first time by deep-level transient spectroscopy (DLTS). One electron trap center at 0.68 eV below the CB is also observed in n-type 6H-SiC. The trap concentration and capture cross section are estimated. The concentration of residual impurities V, Cr, Fe and Ti are found to be high. The origin of observed trap centers is discussed with respect to the residual impurities and available information.
Direct Growth of AlGaAs/GaAs Single Quantum Wells on GaAs Substrates Cleaned by Electron Cyclotron Resonance (ECR) Hydrogen Plasma
Authors: Kondo Naoto , Yasushi Nanishi Yasushi Nanishi , Masatomo Fujimoto Masatomo Fujimoto
Published: October 2002

Direct growth of AlGaAs/GaAs single quantum wells (SQWs) on GaAs substrates without growing buffer layers is carried out by using electron cyclotron resonance (ECR) hydrogen plasma cleaning. SQW structures are successively grown by molecular beam expitaxy (MBE) after the cleaning process without breaking the vacuum. Photoluminescence shows intense and narrow spectra, in clear contrast to that of conventional thermal cleaning. Atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) analyses show that surface roughness and interface impurity accumulations are significantly reduced as well. A flat and clean surface obtained by plasma cleaning improves the quality of grown layers.
Crystal Growth Mechanism of YBa2Cu3Ox from Coexisting Region of Solid with Melt
Authors: Asaoka Hidehito , Takei Humihiko , Kenji Noda Kenji Noda
Published: October 2002

The behavior of textured growth of YBa2Cu3O

x

(123) from Y2BaCuO5 (211) and melt has been investigated using polarized optical microscopy, electron microprobe analysis and the X-ray powder diffraction method. The observations of growing interfaces of the solidified 123 phase in three-phase region, 123, 211 and the melt revealed the occurrence of diffusion of the 123 phase to the surrounding melt. This fact suggests the solubility of the 123 phase to the melt, and induction of the Ostwald ripening, which acts on the solid-melt interfaces to lower the interface free energy of the growing crystals. These situations lead to the growth of 123 crystals which progresses due to the aid of the peritectic reaction between 211 and the surrounding melt phases.
Structure and Superconducting Properties of HgBa2CaCu2Oy Films Prepared by Laser Ablation
Authors: Miyashita Shoji , Hiroko Higuma Hiroko Higuma , Fusaoki Uchikawa Fusaoki Uchikawa
Published: October 2002

Hg-1212 films were prepared on the (100) SrTiO3 substrate by laser ablation and subsequent annealing. The as-grown film was annealed with a Hg-1212 bulk pellet in a quartz tube. The superconducting transition temperature T
c(onset) was 123 K and T
c(ρ=0) was 97 K. This film was shown to have a preferential orientation of the c-axis perpendicular to the (100) SrTiO3 substrate, and was composed of Hg-1212 platelike grains and Ba–Cu–O compounds.
Visible Photoluminescence from Anodically Oxidized Porous Silicon
Authors: Ito Toshimichi , Motoi Kenji , Arakaki Osamu , Akimitsu Hatta Akimitsu Hatta , Akio Hiraki Akio Hiraki
Published: October 2002

Porous silicon (PS) anodically oxidized just after anodization of a silicon wafer has been investigated. Room-temperature photoluminescence (PL) peaks shifted to shorter wavelengths at the initial oxidation stage, followed by the PL blue shift saturation upon further oxidation. The temperature coefficient of the PL peak energy was -0.2 meV/K in the former while it was -0.5 meV/K in the latter. PL excitation spectra around 4 eV also showed changes corresponding to the PL blue shifts with oxidation. The PL mechanism is discussed in relation to band-gap widening due to the size reduction effect and appearance of luminescence centers.
Dynamic Response of Surface-Stabilized Ferroelectric Liquid Crystals: Effect of Alignment Films
Authors: Munehiro Kimura Munehiro Kimura , Michinori Nishikawa Michinori Nishikawa , Tadashi Akahane Tadashi Akahane , Shunsuke Kobayashi Shunsuke Kobayashi
Published: October 2002

The dynamic response of Surface-Stabilized Ferroelectric Liquid Crystals (SSFLCs) with several orientational polyimide films which have different chemical structures was investigated. The experimental results examined by switching current and transitional dielectric constant measurement methods were compared qualitatively with the numerical calculations based on the continuum theory. It is proposed that the degree of anchoring strength is obtained by measuring the dynamic responses. The difference of the surface anchoring strength seems to be attributable to the physicochemical interaction between the polyimides and the FLC molecules.
Dissipation of Contact Electrified Electrons on Dielectric Thin films with Silicon Substrate
Authors: Okusako Takahiro , Uchihashi Takayuki , Nakano Akihiko , Ida Toru , Yasuhiro Sugawara Yasuhiro Sugawara , Seizo Morita Seizo Morita
Published: October 2002

We studied microscopic contact electrification on three different kinds of dielectric thin films with the same silicon substrate, i.e., SiO2/Si, Si3N4/SiO2/Si (NOS) and SiO2/Si3N4/SiO2/Si, using a modified atomic force micro- scope (AFM). From the results, we clarified that reproducible and controllable contact electrification is possible on each sample. From the time evolution of the peak values and full widths at half-maximum (FWHMs) of electrostatic force due to contact-electrified electrons, we found that the stable-unstable phase transition occurs only on SiO2/Si and SiO2/Si3N4/SiO2/Si thin films with the SiO2 surface.
Optical Properties of LiNbO3 Implanted with Ag+ Ions
Authors: Deying Shang , Yukinori Saito Yukinori Saito , Shinji Suganomata Shinji Suganomata
Published: October 2002

Ag+ ions were implanted into LiNbO3 held at room temperatures with the energy of 25 keV in the range of 2×1015 to 8×1016 ions/cm2. Absorption in the visible range was measured. LiNbO3 implanted with Ag+ ions shows brilliant reddish-violet and a large absorption peak at about 520 nm. Ag atoms aggregate during implantation and form very small flat particles of the size of about 0.3 to a few micrometers in surface layers of depths up to 16 nm.
Epitaxial Growth of AgGaS2 on (100) GaAs by Excimer Laser Deposition
Authors: Uchiki Hisao , Hiroyuki Hirasawa Hiroyuki Hirasawa , Isao Hasegawa Isao Hasegawa
Published: October 2002

Epitaxial AgGaS2 films were grown on (100) GaAs substrates by means of XeCl excimer laser deposition. Mixed powders of Ag2S and Ga2S3 were used as a target. The diffraction lines from the (004) and (008) planes of AgGaS2 appeared in an X-ray diffraction pattern. Weak, possibly excitonic, band-edge emission and intense broad green emission were observed in photoluminescence spectra upon excitation by the 365 nm line from a Hg-Xe lamp.
Electromigration Resistance Measurements of Multilayered Interconnections by Short Test Lines
Authors: Fukada Shin-ichi , Hirasawa Masayoshi , Suzuki Masayuki
Published: October 2002

The electromigration performance of Al/W bilayered interconnections was investigated. The cumulative failure plots deviate from the usual two-parameter log-normal distribution for some test conditions, and incubation time is needed as a third parameter to fit the plots to an ideal curve. The incubation time can be found more easily as the gradient of the cumulative failure density plot becomes smaller. Shortening the sample line length is effective in decreasing the gradient of the plot. Decreasing the damaged point density in interconnections has the same effect as shortening the test line length. In interconnections having a low damaged point density, the reliability will be limited by weak points within a few of the test lines, even though the average lifetime is improved. The incubation time is necessary as another parameter to evaluate the reliability of such interconnections accurately.
Relationship between Nitrogen Profile and Reliability of Heavily Oxynitrided Tunnel Oxide Films for Flash Electrically Erasable and Programmable ROMs
Authors: Arakawa Tomiyuki , Hayashi Takahisa , Ohno Morifumi , Matsumoto Ryoichi , Uchiyama Akira , Fukuda Hisashi
Published: October 2002

A larger charge-to-breakdown value and much less threshold-voltage narrowing in the endurance properties of flash electrically erasable and programmable ROMs were achieved by incorporating a greater amount of nitrogen ( ∼1021 atoms/cm3) into the bulk of thin oxide films, as well as near the oxide/Si interface. The charge to breakdown value of thin oxide films formed under an optimized heavy oxynitride condition (dry oxidation at 1100° C; NH3 annealing at 1000° C for 30 s; N2O annealing at 1100° C for 30 s) was four times as large as that of a conventional dry oxide film. These results were attributed to the suppression of stress-induced charge traps and the interface state, due to the introduction of nitrogen atoms in the oxide bulk, as well as at the oxide/Si interface.
High-Reliability Copper Interconnects through Dry Etching Process
Authors: Igarashi Yasushi , Yamanobe Tomomi , Toshio Ito Toshio Ito
Published: October 2002

A modified high-temperature dry etching technique, which enables anisotropic patterning with a high etching selectivity and self-aligned passivation of a sidewall of an interconnect simultaneously, has been developed for fabrication of sub-quarter-micron Cu interconnects. Resistivities of the resulting Cu interconnects are in the range of 1.7 to 2.2 µΩ· cm for the linewidth of 0.2-3.0 µ m. As a result of electromigration (EM) tests, it has been observed that median time to failure (MTF) of the Cu interconnects depends on their linewidth. This behavior is considered to be caused by their grain structure, such as a bamboo-type structure for linewidths narrower than 0.3 µ m. In comparison with a MTF of a conventional Al-1%Si line, these Cu interconnects have at least 100 times longer lifetime. Activation energy for EM damage of the 0.7-µ m-wide line is 0.88 eV.
Ammonium-Salt-Added Silica Slurry for the Chemical Mechanical Polishing of the Interlayer Dielectric Film Planarization in ULSI's
Authors: Hayashi Yoshihiro , Sakurai Michio , Nakajima Tsutomu , Hayashi Kanji , Sasaki Syuzo , Chikaki Shin-ichi , Takemitu Kunio Takemitu Kunio
Published: October 2002

Based on the theory of colloid, a new KOH-free silica slurry is developed for chemical mechanical polishing (CMP) to planarize the interlayer dielectric films in ULSI's. The ammonium salt addition to the slurries of pH=6-7 promotes the silica particle agglomeration in the slurry, and enlarges the effective abrasive particle size. The particle agglomeration yields a high polishing rate due to increasing of the mechanical effect, and good particle removability with scrub cleaning is achieved. The ammonium salt-added slurry provides the high-speed CMP without alkaline-metal contamination to the LSI fabrication line.
Local Vortex Generation and Detection by Integrated DC Superconducting Quantum Interference Devices*
Authors: Peter Frank , Grimm Michael , Mück Michael , Heiden Christoph
Published: October 2002

A test circuit for the local generation and detection of single vortices has been fabricated, based on a multilayer structure with low-pinning e-beam evaporated Nb and high-pinning reactively sputtered NbN films. The generation of vortices is performed by a current through a control line perpendicular to a low-pinning channel. For the detection and determination of the position of generated vortices, several dc superconducting quantum interference devices (SQUID) were located around the low-pinning channel and the control line. The presence of single vortices in the channel led to a shift in the dc SQUID flux-to-voltage transfer function. By computer simulations of the flux that a single vortex generates at the position of the SQUIDs, the number and location of generated vortices could be determined. The spatial resolution of this procedure was determined to be about ±1 µ m normal to and ±2 µ m along the channel.
Film Quality Dependence of Adaptive-Learning Processes in Neurodevices Using Ferroelectric PbZrxTi 1-xO3 (PZT) Films
Authors: Tokumitsu Eisuke , Nakamura Ryo-ichi , Itani Kensuke , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

Partial switching in ferroelectric PbZr

x

Ti1-
x

O3 (PZT) thin films has been studied for adaptive-learning metal-ferroelectric-semiconductor field-effect transistor (MFSFET) applications. In particular, the effects of film quality on adaptive-learning processes in ferroelectric PZT thin films are discussed. Dimensionality factor n of the ferroelectric domain growth is estimated to be 1.3-1.4 for sol-gel grown PZT films and 2.0-2.1 for vacuum-evaporated materials. It is shown that this discrepancy results in the difference of the adaptive-learning processes. It is also demonstrated that the learning process in PZT films can gradually proceed by applying the short input pulses.
Influences of Sb on the Growth and Properties of CuInSe2 Thin Films
Authors: Tseng Bae-Heng , Chang Geon-Wen , Song-Bin Lin Song-Bin Lin
Published: October 2002

The growth of CuInSe2 film in the presence of an Sb beam results in a great improvement in surface morphology and grain structure. It is attributed to the surfactant modified growth caused by the Sb atoms. A p-type CuInSe2 film with a resistivity of about 0.05 Ω- cm was obtained, which is comparable with the resistivity of a Cu-rich film grown without Sb. Photoluminescence measurements also show that the luminescence intensity of the films grown with Sb is much higher than that of the films grown without Sb having similar compositions. It is probably due to the improvement in the grain structure as well as the crystallinity within the grains.
Two-Dimensional Growth of GaN on Various Substrates by Gas Source Molecular Beam Epitaxy Using RF-Radical Nitrogen Source
Authors: Kikuchi Akihiko , Hoshi Hiroyuki , Katsumi Kishino Katsumi Kishino
Published: October 2002

Two-dimensional layer-by-layer growth conditions for GaN epitaxial layers by gas source molecular beam epitaxy (MBE) using a 13.56 MHz RF-radical nitrogen source were systematically investigated. As the growth rate was decreased, the reflection high-energy electron diffraction patterns of the GaN epitaxial layers grown on (0001) Al2O3 were changed from spotty patterns to streak ones in the earlier stage of GaN growth. It was clearly indicated that the lower growth rate (R<0.1 µ m/h) enhanced the two-dimensional growth. Furthermore, the introduction of the annealed GaN buffer layers (60 Å) drastically enhanced the two-dimensional growth of the layers on (0001) Al2O3, (001) MgO and (001) GaAs substrates. The surface morphology dependence on substrate materials was also described.
Disordering of CdZnSe/ZnSe Strained Layer Superlattices by Ion Implantation
Authors: Yokogawa Toshiya , Merz James , Luo Hon , Furdyna Jack , Lau Sylvanus , Kuttler Marc , Bimberg Dieter
Published: October 2002

We report the first confirmation of disordering of CdZnSe/ZnSe strained-layer superlattices (SLSs) by ion implantation. Ne was used for the ion species. Both the as-grown sample and the sample annealed without ion implantation showed periodic depth profiles in secondary ion mass spectrometry (SIMS) analyses and several orders of well-resolved double-crystal X-ray satellite peaks due to SLS periodic structure. However, the SIMS periodic profiles and the satellite peaks completely disappeared in the Ne-implanted sample, indicating that the SLS structure was disordered by the ion-implantation and not caused by the annealing process.
Schottky Contacts on n-InP with High Barrier Heights and Reduced Fermi-Level Pinning by a Novel In Situ Electrochemical Process
Authors: Wu Nan-Jian , Hashizume Tamotsu , Hasegawa Hideki , Amemiya Yoshihito
Published: October 2002

Schottky contacts on n-InP were fabricated by a novel in situ electrochemical process. The characteristics of the Schottky contacts were investigated using atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), current-voltage (I-V) and capacitance-voltage (C-V) techniques. The results of AFM and XPS measurements indicate that the novel in situ electrochemical process produces smooth and oxide-free interfaces. The Schottky contacts show nearly ideal thermionic emission characteristics. The novel electrochemical process was found to reduce Fermi-level pinning at the Schottky contact interfaces. The Schottky barrier height was found to change over a wide range from 0.35 eV to 0.86 eV, depending on the work function of the contact metals. The Pt/InP contact gave the highest barrier height of 0.86 eV.
Effects of Sulfur Treatment and Hydrogen Plasma Treatment on GaAs
Authors: Oh Yong Thak , Chung Chun Ki , Eom Gi Seog , Kang Tae Won , Hong Chi Yhou , Park Sung Bae , Kim Tae Whan
Published: October 2002

Photoluminescence (PL) and photoreflectance (PR) measurements have been carried out to investigate the surface state behavior for sulfur-treated GaAs as well as the neutralization effect on the carbon acceptors for hydrogen- or nitrogen-plasma-treated GaAs. Whereas the intensity of the PL signal for the sulfur-treated GaAs increased monotonically as the sulfur-treatment time increased, the intensity of the PR signal increased until the sulfur treatment time of 110 min, and thereafter decreased. These results indicate that a decrease in the number of the surface states and the formation of a quasi-flat band as a result of the sulfur treatment. After the GaAs was hydrogen-plasma-treated and annealed at 400° C, the relative PL intensity ratio between the donor-bound exciton and the carbon acceptor increased by a factor of 2, and a variation in the PR broadening parameter was induced by neutralization of the carbon acceptors due to the combination of the hydrogenic ions and the carbon ions in the GaAs. Variation in the surface states and neutralization of the ions affect the intensity of the PL spectra and the intensity and the broadening parameter of the PR signal.
Direct Patterning of the Current Confinement Structure for p-Type Column-III Nitrides by Low-Energy Electron Beam Irradiation Treatment
Authors: Inamori Masahiko , Sakai Hiromitsu , Tanaka Toshiyuki , Amano Hiroshi , Isamu Akasaki Isamu Akasaki
Published: October 2002

Partial low-energy electron beam irradiation (LEEBI) treatment was used to fabricate UV/blue light-emitting devices based on column-III nitrides having a directly patterned current confinement structure. The newly developed devices show very low leakage reverse current, stable operation at high pulsed current injection, and strong and narrow violet emission at room temperature.
Analysis of Switching Time of Monostable-Bistable Transition Logic Elements Based on Simple Model Calculation
Authors: Koichi Maezawa Koichi Maezawa
Published: October 2002

In this study, the operation speed of monostable-bistable transition logic elements (MOBILEs) is analyzed based on an equivalent circuit model. First, the intrinsic operation speed is examined independent of the subsequent stages. The results show that high-speed operation close to the intrinsic response time of resonant tunneling diodes is possible under the appropriate conditions. It is also shown that the most important factor limiting the operation speed is the angle of the crossing at the unstable point in the load-line diagram, which dominates the potential curve. Next, the effects of the input capacitance of the subsequent stages are examined to clarify the operating frequency under practical conditions. The importance of reducing the input capacitance is shown for high-speed operation.
Elastic Scattering and Depletion Effects on Current-Voltage Characteristics of Gated Resonant Tunneling Diodes
Authors: Chomsik Lee Chomsik Lee
Published: October 2002

Numerical solutions to the two-dimensional Poisson equation and the continuity equation have been used to calculate the lateral depletion region and carrier concentrations by the finite difference method. Simulation of the gated resonant tunneling diode (GRTD) using a self-consistent quantum model shows depletion effects on current-voltage characteristics. In the bias conditions whereby the GRTD reaches zero dimension in the well region, we consider elastic scattering mechanisms and the presence of evanescent modes to calculate resonant tunneling transmission coefficients. We present the effects of subband mixing and elastic scattering in a two-dimensional simulation of the current-voltage characteristics of the GRTD.
The effect of this scattering results in shifting and broadening of the tunneling probability, and reduction of its peak value.
Hot Electron Effects in Infrared Multiple-Quantum-Well Phototransistor
Authors: Victor Ryzhii Victor Ryzhii , Maxim Ershov Maxim Ershov
Published: October 2002

This paper presents a theoretical analysis of physical mechanisms responsible for operation and performance, in particular, optical gain, of infrared multiple-quantum-well (MQW) photodetectors. The influence of the device structure on the distribution of potential, which, in turn, determines the carrier injection and transport properties, is discussed. We studied the hot electron effects in the MQW phototransistor, which has wide triangular emitter and collector barriers and an equipotential base. It is shown that the hot electron transport in the base, provided by a wide gap emitter, can give rise to a very high values of optical gain, as high as 1000.
Analysis of Distributed Feedback Semiconductor Laser-Electroabsorption Modulator Integrated Light Source, Including Gain-Coupled Structure
Authors: Si Weimin , Luo Yi , Li Dejie , Zhang Keqian , Nakano Yoshiaki , Tada Kunio
Published: October 2002

Taking into consideration of gain coupling, characteristics such as single-mode selectivity, chirping and light output efficiency of photonic integrated circuits (PIC) integrating distributed feedback (DFB) semiconductor lasers and electroabsorption modulators are analyzed for the first time. Devices with conventional index-coupled (IC), quarter-wave-shifted (QWS) and gain-coupled (GC) DFB laser sections are calculated and compared. The chirping of GC-PIC is nearly the same as that of IC-PIC and QWS-PIC, but the single-mode selectivity of GC-PIC is much better. With a [HR-AR] coating , which is advantageous for high-power operation, GC-PIC shows a much higher probability of single-mode operation than IC-PIC, while QWS-PIC does not function at all.
First Fabrication of AlGaAs/GaAs Double-Heterostructure Light-Emitting Diodes Grown on GaAs(111)A Substrates Using Only Silicon Dopant
Authors: Egawa Takashi , Niwano Yutaka , Fujita Kazuhisa , Nitatori Kouichi , Watanabe Toshihide , Jimbo Takashi , Umeno Masayoshi
Published: October 2002

We have grown an AlGaAs/GaAs double-heterostructure (DH) light-emitting diode (LED) on a GaAs(111)A-5°-misoriented substrate using only Si dopant by molecular beam epitaxy. Conduction type and carrier concentration were controlled by flux ratio and Si cell temperature. Smooth heterointerfaces were also obtained. The p-n junction showed a turn-on voltage of 1.2 V and a reverse voltage of 2.5 V at 1 mA.
The AlGaAs/GaAs LED exhibited dc operation at 300 K.
The optical output power was 30 nW at 150 mA, and the peak in the spectrum was 875 nm with the full width at half-maximum of 28 nm.
Effects of Power Loss Reduction with Ferrite Magnetic Wedge on Capacitor Motor
Authors: Kaga Akio , Tajima Katsubumi , Yokawa Norihiko , Tadahito Itoh Tadahito Itoh
Published: October 2002

The authors have inserted ferrite magnetic wedges into the stator slot openings of the capacitor motor to decrease the pulsation of flux density distribution in the air gap. As a result, the iron loss was reduced greatly to increase the motor efficiency and to improve other running characteristics.
Single-Chip Integration of Light-Emitting Diode, Waveguide and Micromirrors
Authors: Nagata Takahiko , Namba Tohru , Kuroda Yasuhide , Miyake Kouji , Miyamoto Takahiro , Yokoyama Shin , Miyazaki Seiichi , Koyanagi Mitsumasa , Hirose Masataka
Published: October 2002

Fundamental technologies for optical interconnection on a Si LSI chip have been developed using conventional silicon process technologies. The optical waveguides with SiO

x

N

y

core and SiO2 cladding layers and Al micromirrors to change the light propagation direction have been fabricated by low-temperature deposition. Moreover, the single test chip integrated with a light-emitting diode (LED), photodiode, waveguides and micromirrors has been fabricated and signal transfer between LED and the photodetector has been achieved.
Preparation of Co Ferrite Films by Plasma-Enhanced Metalorganic Chemical Vapor Deposition
Authors: Fujii Eiji , Torii Hideo , Takayama Ryoichi , Takashi Hirao Takashi Hirao
Published: October 2002

Thin films of Co ferrite and Co-Zn ferrite ( Co1-
x

Zn

x

Fe2O4, 0≤x≤0.5) with partial preferential orientation of the (100) plane parallel to the film surface were prepared on soda-lime glass substrates at 400° C by plasmaenhanced metalorganic chemical vapor deposition. Faraday rotation of the CoFe2O4 film took the negative maximum value of -2.8×104 deg/cm near 700 nm in the wavelength range from 550 nm to 1100 nm. The Faraday hysteresis loop indicated that the CoFe2O4 film had perpendicular magnetic anisotropy, which was caused mainly by the intrinsic stress-induced uniaxial anisotropy. Faraday rotation at 800 nm and Curie temperature decreased with increasing Zn content x.
Quantized Conductance of a Silicon Wire Fabricated by Separation-by-Implanted-Oxygen Technology
Authors: Yasuyuki Nakajima Yasuyuki Nakajima , Yasuo Takahashi Yasuo Takahashi , Seiji Horiguchi Seiji Horiguchi , Kazumi Iwadate Kazumi Iwadate , Hideo Namatsu Hideo Namatsu , Kenji Kurihara Kenji Kurihara , Michiharu Tabe Michiharu Tabe
Published: October 2002

Ultra-fine silicon wires have been fabricated by SIMOX (Separation by IMplanted OXygen) technology, electron beam lithography, anisotropic chemical etching, and thermal oxidation. The silicon wires have a trapezoidal cross-sectional shape and are fully surrounded by SiO2, as confirmed by transmission electron microscopy. The size of the wires is controlled by using the fabrication method proposed here, as measured by scanning electron microscopy. A wire 20 nm wide and 6 nm high exhibits quantized conductance at 26 K, and conductance steps remain up to 60 K. In the case of a wire 17 nm wide and 4 nm high, steplike structures in the conductance versus gate voltage curve persist over 100 K. These results are attributed to the large subband energy spacing in the narrow wire region, where electrons are physically confined by the high potential of the SiO2 barrier.
Control of Current in 2DEG Channel by Oxide Wire Formed Using AFM
Authors: Ishii Masami , Kazuhiko Matsumoto Kazuhiko Matsumoto
Published: October 2002

We have succeeded in depleting a two-dimensional electron gas channel using an oxide wire formed with an atomic force microscope. Currents in the channel depend on the height of the oxide wire on the delta-doped high-electron-mobility transistor. The current in the sample with a 20 nm-thick oxide wire is approximately one hundred times lower than that without the wire.
Vertical Transport Properties of Photogenerated Carrier in InGaAs/GaAs Strained Multiple Quantum Wells
Authors: Kitatani Takeshi , Yazawa Yoshiaki , Minemura Junko , Tamura Katsumi , Terunori Warabisako Terunori Warabisako
Published: October 2002

We report on the carrier transport properties of a GaAs p-i-n structure including In

x

Ga1-
x

As/GaAs (x=0-0.15) strained multiple quantum wells (MQWs). Photocurrent measurements at room temperature showed that the spectral response extended to lower energies with increasing In content, and the quantum efficiency (ratio of the number of photogenerated carriers contributing photocurrent to the number of absorbed photons) was almost unity even when the well depth was several times greater than the thermal energy k
T at room temperature. This is consistent with the calculation of the time for carriers to escape from the InGaAs/GaAs single quantum well. The calculation result also shows that applying a high electric field increases the photocurrent gain in MQW diodes.
Bloch Oscillations in Semiconductor Superlattices
Authors: Kö Hartmut G. Roskos , Heinrich Kurz Heinrich Kurz
Published: October 2002

A brief summary of the time-resolved investigation of Bloch oscillations of electron wave packets in semiconductor superlattices is given. Focussing on the emission of coherent terahertz-frequency electromagnetic radiation by Bloch oscillations, new experimental and theoretical results are presented. In all experiments published so far, Bloch oscillations have been induced by simultaneous impulsive optical excitation of several excitonic Wannier-Stark states at the bandedge of the first electron miniband. Here, we report on the first observation of Bloch oscillations induced by photo-excitation of continuum states as high as 100 meV above the fundamental bandgap. We then address the feasibility of optically pumped Bloch (or Esaki-Tsu) oscillators as a practical source for electromagnetic signals with a frequency continuously tunable from several hundred GHz to at least 6 THz. Advantage is taken of the supperradiant character of the emission process. The emission efficiency is discussed and concepts for an increase of the output power are proposed.
Fuzzy Analysis of the Linear Equivalent for Fabricating a Holographic Optical Element in Photoresist
Authors: Seng Chang Rong , Pio Hu Chern Sheng Lin
Published: October 2002

In this paper fuzzy analysis for economically fabricating a holographic optical element (HOE) in photoresist is conducted. We find that the grating profile has a close relationship with diffraction efficiency, and that the process parameters influence the grating profile significantly. Thus, using the fuzzy control in these relations, it becomes possible to predict the diffraction efficiency and to solve many problems in the grating fabrication process. From the modulation mechanism in these complex holograms we believe we have extracted the necessary and intrinsic qualities, and our model of fuzzy set analysis produces good general agreement with the experimentally measured diffraction efficiency. The new concepts of the “linear equivalent" which we established to simplify a HOE from a honeycomb structure to a linear one will be helpful for processing various types of HOEs.
Crystallizing Mechanism and Recording Properties of In3SbTe2 Phase-Change Optical Disks
Authors: Naruse Atsuko , Ikuta Isao , Andoh Hisashi , Sato Yoshio , Minemura Hiroyuki
Published: October 2002

The crystallization mechanism and its application to improvement of the carrier-to-noise ratio (CNR) for In3SbTe2 phase-change optical disks were examined by that transmission electron microscopy (TEM). The TEM images indicated: (1) mark shapes were distorted when the interval between laser irradiations was short; (2) following dc laser irradiation onto the marks, crystallization proceeded only along the periphery of the amorphous phase; and (3) mark shapes were varied corresponding to the dc laser power. We assumed that the crystallization mechanism for In3SbTe2 was dominated by crystalline growth rather than nucleation. Then we simulated the mark shapes after dc irradiation. By controlling the thermal distribution on the marks, the CNR was improved promoted. We found that dc irradiation was a simple way of improving recording properties.
Convolution-Fitting Method for Doppler-Broadening Plasma Ion Temperature Measurement
Authors: Mikio Mimura Mikio Mimura , Kuninori Sato Kuninori Sato
Published: October 2002

To estimate the ion temperature of plasma using Doppler broadening with a low-resolution monochromator, a convolution-fitting method was proposed. This method utilizes the information of the slit function of the monochromator to improve the effective resolution. It consists of a convolution calculation of trial functions and the slit function, and a fitting of the result with a measured line spectrum. A model experiment was carried out to demonstrate the usefulness of the method. The measured lines were C III 2296.8 Å and C V 2270.9 Å from JIPP T-IIU Tokamak. The slit function was obtained by measuring Hg I 2656.5 Å line from a mercury lamp. Applying the method to these lines, effective resolution was improved by a factor of about seven.
Shift/Rotational-Invariant and Nonuniform Irradiance Pattern Recognition
Authors: Cheng Yih-Shyang , Tsair-Chun Liang Tsair-Chun Liang
Published: October 2002

A composite filter combining a 2-Dimension (2-D) symmetrical Mexican-hat wavelet filter and circular harmonic filter is used to perform shift- and rotational-invariant optical pattern recognition. Simulation results have shown that the method yields correlation output, in terms of correlation peak sharpness and peak-to-sidelobe ratio, the same as or better than that produced by others. The light efficiency of the proposed filters is comparable to that of a circular harmonic filter. Furthermore, even when the input pattern is of various nonuniform irradiances, the filter can recognize them.