bluuebunny/crossref_metadata_2025 huggingface dataset:
Gray-Scale Characteristics in High-Tilt-Angle Ferroelectric Liquid Crystal
Authors: Biradar A. M. , Bawa S. S. , E. P. Haridas E. P. Haridas , S. Chandra S. Chandra
Published: October 2002

The gray-scale characteristics has been observed in a high-tilt-angle ferroelectric liquid crystal, possessing Isotropic-chiral nematic-smectic C* phase transition in a thin and polymer rubbed surface of the sample. The results have been analysed by electrical and optical method. It has been found that the gray-scale characteristics appear because of the strong anchoring effect on polymer rubbed surface due to the unwinding and winding of the smectic layer twisted structure which is present very close to the rubbed surface.
Competition between the Screening Effect and Exchange Interactions in the System CeCu1-xAl3+x ( 0≤x≤0.25)
Authors: Lee Wun-Hsin , Yeh Mei-Rung , Dung-Chung Wang Dung-Chung Wang , Fu-An Yang Fu-An Yang
Published: October 2002

Magnetic measurements on three alloys in the series CeCu1-
x

Al3+
x

(x=0, 0.16, 0.25) reflect the increasing strength of exchange interactions with Al concentration. As determined by ac susceptibility measurements, the Néel temperatures are 2.5, 2.7 and 3.3 K for the three samples x=0, 0.16 and 0.25, respectively. Specific data for CeCuAl3 show that the entropies associated with the magnetic ordering accounts for only ∼ 40% of the theoretically expected Rln2 entropy. The s ubstitution of Cu by Al in CeCu1-
x

Al3+
x

, which increases the average conduction electron density, seems unable to attenuate the localized Ce-4f moments. These results suggest that the RKKY interactions surpass the tendency of the conduction electrons to screen the Ce-4f moments in this system.
Application of Radio-Frequency Discharged Plasma Produced in Closed Magnetic Neutral Line for Plasma Processing
Authors: Taijiro Uchida Taijiro Uchida
Published: October 2002

A new plasma processing method is presented. Use of plasma produced in a closed magnetic neutral line is essential and the merit is easily illustrated in principle with a preliminary experimental result. This method is considered to be useful for many kinds of plasma processing.
Precursors in Atmospheric-Pressure Chemical Vapor Deposition of Silica Films from Tetraethylorthosilicate/Ozone System
Authors: Adachi Motoaki , Okuyama Kikuo , Tohge Noboru , Shimada Manabu , Sato Jun-ichi , Muroyama Masakazu
Published: October 2002

In order to clarify the mechanisms of film formation in an atmospheric-pressure chemical vapor deposition reactor using the tetraethylorthosilicate/O3/He system, the contents of C, H, and SiO2 in the intermediate species were estimated from both CHN elemental chemical component and thermogravimetric analyses of simultaneously generated nanometer-sized particles. From the results of compositional analysis of intermediate species and SEM observation of resultant films, the intermediate species which form films with excellent flow-like shape were found to contain relatively large amounts of ethoxy group and small amounts of hydroxyl group.
Application of Maximum Entropy Method for Data Processing of Microwave Reflectometry
Authors: Nagatsu Masaaki , Hayashi Takashige , Tsukishima Yoshiko Matsuhisa
Published: October 2002

One-dimensional full wave analysis shows that simultaneous reflections from the O-mode and X-mode cutoff layers will occur through the mode-coupling process in a plasma with a sheared magnetic field. In this letter, we propose and examine signal processing using the maximum entropy method to overcome the problem caused by simultaneous reflection. It has been shown that the proposed method is effective for obtaining cutoff positions precisely not only in case of mixed, simultaneously-reflected signals but also in case of a noisy signal.
Studies on Positive Ion Behavior in Reactive Sputtering of Yttria-Stabilized Zirconia (YSZ)
Authors: Hata Tomonobu , Matsuda Hideki , Ryo Ando Ryo Ando , Susumu Horita Susumu Horita
Published: October 2002

Yttria-stabilized zirconia (YSZ) thin films were deposited by reactive sputtering. Various hysteresis curves, such as those in deposition rate and discharge voltage, were observed as functions of oxygen flow rate: The O2
+, Zr+, Y+, YO+, ZrO+, ZrO2
+ ions incident on the substrate were analyzed by a quadrupole mass spectrometer (QMS) and their behavior during the course of deposition was observed in detail. It is concluded that the Y/Zr ratio in the metallic film is exactly estimated as the arrival ratio of Y+/Zr+.
Atomically Resolved Image of Cleaved GaAs(110) Surface Observed with an Ultrahigh Vacuum Atomic Force Microscope
Authors: Ohta Masahiro , Sugawara Yasuhiro , Hontani Kouji , Morita Seizo , Osaka Fukunobu , Suzuki Mineharu , Nagaoka Hideki , Mishima Shuzo , Okada Takao
Published: October 2002

The first demonstration of atomic-resolution imaging of a GaAs(110) surface with an ultrahigh vacuum atomic force microscope (UHV AFM) is performed. A rectangular lattice with spacing of 5.7±0.5 Å×4.0±0.4 Å is resolved. This result suggests that the UHV AFM has potential capability for investigating semiconductor surfaces having dangling bonds on an atomic scale.
Total Photo-Yield Imaging of Stripe Patterns Using Soft X-Ray Microbeam Formed by Wolter-Type Mirror
Authors: Ken Ninomiya Ken Ninomiya , Masaki Hasegawa Masaki Hasegawa
Published: October 2002

One-dimensional imaging of stripe patterns was performed using the total yield of photoelectrons generated by the irradiation of a 150 eV soft X-ray microbeam formed by a Wolter-type mirror. The samples were aluminum stripes, which were patterned on a SiO2 wafer with the same widths and spacing of either 2 or 4 µ m. When the sagittal beam size of the microbeam was between 1.8 and 3.8 µ m, the patterns were detected with a modulation between 0.06 and 0.11. The imaging indicates that the highest lateral resolution achieved is between 0.7 and 1.3 µ m, when the resolution is defined as the 25%–75% width of the photoelectron count rate change at the pattern edge.
A2Nb1+XOY (A=Ca, Sr) ( 0\lesssimx\lesssim5): New Reduced Niobate Superconductors with the Distorted Defect-Perovskite Structure
Authors: Akio Nakamura Akio Nakamura
Published: October 2002

From the DC magnetization and powder X-ray diffraction (XRD) measurements, in the defect-perovskitc-type reduced niobates A2Nb1+
X

O

Y

(A=Ca, Sr), we found at least two kinds of broad superconducting phases with the critical temperatures of about 9.2 K (for 0\lesssimx\lesssim1.0) and 8.3 K (for 1.2–1.5\lesssimx\lesssim5.0) covering almost the whole valence state of Nb from Nb1+ to Nb5+ in the Ca system and in the somewhat narrower range in the Sr system. The highest shielding effect in these phases of both systems is attained for samples prepared from the starting mixtures having the initial mean Nb valence between 1+ and 2+.
Structure and Superconducting Properties of Y–Pd–B–C System
Authors: Fujii Hiroki , Ikeda Shozo , Kimura Takashi , Arisawa Shun-ichi , Hirata Kazuto , Kumakura Hiroaki , Kazuo Kadowaki Kazuo Kadowaki , Kazumasa Togano Kazumasa Togano
Published: October 2002

A superconducting phase with transition temperature of 23 K found in the Y–Pd–B–C system was identified to have a body-centered tetragonal structure with the lattice parameters of a=0.38 nm and c=1.08 nm. The phase is of a platelike shape embedded in a matrix of other phases. The composition ratio of the superconducting phase determined using an electron probe X-ray microanalyzer is YPd2B2C1.5, although there may be uncertainty of the C concentration. The observation by high-resolution transmission electron microscopy indicates that the crystal structure is very similar to that reported recently for the superconducting LuNi2B2C intermetallic compound.
Photoluminescence and Raman Studies of Zn0.7Cd0.3Se/ZnSe Short Period Strained-Layer Superlattices Grown by Hot Wall Epitaxy
Authors: Hassan H. Abu , J. Y. Jen J. Y. Jen , Yasuo Oka Yasuo Oka
Published: October 2002

Optical and structural studies on short period Zn0.7Cd0.3Se/ZnSe strained-layer superlattices (SLS) grown by hot wall epitaxy have been performed experimentally using photoluminescence and Raman scattering. We have found an additional luminescence peak (in our shorter period SLS) at higher energy than the dominant exciton transition peak. From our Raman scattering measurements and a Kromg-Penney model for calculating excitonic transitions in quantum wells, this phenomenon can be interpreted in terms of monolayer-type interface fluctuation.
Trains of Flux Jumps Observed in a Quench-and-Melt-Grown YBa2Cu3O7 under Pulsed Magnetic Field
Authors: Itoh Takeo Takizawa , Tanimura Yoshinobu , Kohji Kanbara Kohji Kanbara , Mitsuru Morita Mitsuru Morita , Misao Hashimoto Misao Hashimoto
Published: October 2002

The motion of quantized fluxes in ring-shaped YBa2Cu3O7 samples has been observed under pulsed magnetic field in the 15 K to critical temperature (T
c) range. Successive flux jumps have been observed in a low-J
c sample, where J
c is the transport critical current density. All these jumps are determined by the Lorentz force, and not by the thermal avalanche conditions. It is suggested that the trains of jumps are caused by the weakened pinning force in a degraded sample.
Effect of Pr Impurity on Blue Tm3+ Luminescence in Y2O2S Phosphor
Authors: Daud Alias , Kitagawa Masahiko , Takeshima Hideaki , Futaki Hisanori , Shosaku Tanaka Shosaku Tanaka , Hiroshi Kobayashi Hiroshi Kobayashi
Published: October 2002

The quenching mechanism of blue Tm3+ luminescence in Y2O2S phosphors due to residual Pr3+ ions has been studied. Results of photoluminescence and excitation spectra measurements and selective excitation measurements of Y2O2S:Tm3+, Pr3+ phosphors show that there is no energy transfer between Tm3+ and Pr3+ centers. The quenching of the blue Tm3+ emission by Pr3+ ions can be ascribed to the large electron-hole capture cross section of Pr3+ centers.
Convenient Spectrum Measurement of Magnetooptic Faraday Effect Utilizing Off-Crossed Polarization
Authors: Imamura Takayuki , Matsumoto Koji , Inoue Mitsuteru , Gomi Manabu , Toshitaka Fujii Toshitaka Fujii
Published: October 2002

A convenient measurement of the magnetooptic Faraday spectra, i.e., the Faraday rotation angle θ F and Faraday ellipticity χ F vs wavelength, is presented based on ellipsometry in which the polarizer and analyzer are set in an off-crossed polarization state. This system is suitable for full computerization, enabling us to achieve efficiency in measurement without loss of accuracy. A very good agreement of the spectra between the present method and an ordinary crossed polarization method was found using a bismuth-substituted yttrirnm-iron-garnet film.
Space Charge Limited Current in Semiconducting Diamond Films
Authors: Matsumae Yoshiaki , Akiba Yukio , Hirose Yoichi , Tateki Kurosu Tateki Kurosu , Masamori Iida Masamori Iida
Published: October 2002

A trap-limited space-charge-limited current (SCLC) in diamond p-i junction diodes is studied. Diodes are prepared by the hot filament chemical vapor deposition method. The SCLC is ascribed to the positive charge due to holes injected from the p-type diamond layer into the intrinsic (i)-type diamond layer. According to the method proposed by Rose [Phys. Rev. 97 (1995) 1538], the existence of trap levels which are distributed exponetially in the energy gap is confirmed. The distribution profile and the concentration of traps per unit energy and cubic centimeter are deduced by examining current-voltage characteristics which are experimentally obtained.
Modulation Voltage of High Tc DC Superconducting Quantum Interference Device with Damping Resistance
Authors: Enpuku Keiji , Doi Hideki , Go Tokita Go Tokita , Taku Maruo Taku Maruo
Published: October 2002

The effect of damping resistance on the voltage versus flux (V -Φ) relation of the high T
c dc superconducting quantum interference device (SQUID) is studied experimentally. Dc SQUID using YBaCuO step-edge junction and damping resistance in parallel with SQUID inductance is fabricated. Measured values of modulation voltage in the V -Φ relation are compared with those of the conventional SQUID without damping resistance. It is shown that modulation voltage is much improved by using damping resistance. The obtained experimental results agree reasonably with theoretical predictions reported previously.
Preparation of CuGaSe2 Heteroepitaxial Layers by Metalorganic Molecular Beam Epitaxy
Authors: Shirakata Sho , Kazuo Morita Kazuo Morita , Shigehiro Isomura Shigehiro Isomura
Published: October 2002

The growth of CuGaSe2 films on a GaAs(100) substrate using cyclopentadienylcoppertriethylphosphine (CpCuTEP) as a Cu source in metalorganic molecular beam epitaxy (MOMBE) has been studied. Epitaxial CuGaSe2 films have been grown at 500°C with the c-axis normal to the substrate plane. Films were characterized by scanning electron microscopy, X-ray diffraction, photoluminescence and photoreflectance techniques.
Transparent and Conductive ZnO Thin Films Prepared by Atmospheric-Pressure Chemical Vapor Deposition Using Zinc Acetylacetonate
Authors: Minami Tadatsugu , Sonohara Hideo , Shinzo Takata Shinzo Takata , Hirotoshi Sato Hirotoshi Sato
Published: October 2002

Highly transparent and conductive undoped and impurity-doped ZnO thin films have been prepared by atmospheric-pressure chemical vapor deposition (CVD) using Zn(C5H7O2)2 as a zinc source. A resistivity as low as 4.6×10-3 Ω · cm and an average transmittance above 85% in the visible range were obtained for undoped ZnO thin films deposited at 550°C using H2O as the oxygen source. Al-doped ZnO films with a resistivity as low as 7×10-3 Ω · cm and an average transmittance above 85% in the visible range were prepared at 350°C by the atmospheric-pressure CVD using Al(C5H7O2)3 as the dopant source. In addition, ZnO films with textured surface (milky films) were easily prepared with thicknesses greater than about 400 nm by the atmospheric pressure CVD.
Propagation of Waves through Magnetized Plasmas in Waveguides
Authors: Susumu Takeda Susumu Takeda
Published: October 2002

The dispersion relation and the wavelength of microwaves required to produce [ECR] plasmas in waveguides are calculated by approximate and exact equations. The maximum values of wavelengths are found at some values of ω
p

2/ω2 near the plasma resonance where ω
c
is slightly larger than ω. Here ω
p
, ω
c
and ω are, respectively, plasma, cyclotron resonance and applied frequencies. A wave can also propagate through a high density magnetized plasma in a waveguide with an extremely small diameter.
Polarization Oscillation of Secondary Electrons Emitted from Au/Fe(110)
Authors: Koike Kazuyuki , Furukawa Takashi , Graham P. Cameron Graham P. Cameron , Yoshimasa Murayama Yoshimasa Murayama
Published: October 2002

We have found that polarization and intensity of secondary electrons emitted from Au/Fe(110) oscillate periodically as functions of Au film thickness, with a period of 15±3 Å and with polarities opposite to each other. This result can be attributed to confined energy states in the Au film.
Time-Delayed Interferometry with Nuclear Resonant Scattering of Synchrotron Radiation
Authors: Hasegawa Yuji , Yoda Yoshitaka , Izumi Koichi , Ishikawa Tetsuya , Kikuta Seishi , Zhang Xiaowei , Sugiyama Hiroshi , Ando Masami
Published: October 2002

Interference of two beams resonantly scattered in an X-ray interferometer has been demonstrated. The interference arises between the beams emitted by different nuclei with some time interval. High visibility interference oscillations show the coherent superpositions, as well as the complete coincidence of these beams in the time domain.
X-Ray Chemical Analysis of Multilayered Thin Films by Scanning Electron Microscopy and Total-Reflection-Angle X-Ray Spectroscopy
Authors: Kyoko Yonemitsu Kyoko Yonemitsu , Noriyoshi Shibata Noriyoshi Shibata
Published: October 2002

Scanning electron microscopy and total-reflection-angle X-ray spectroscopy (SEM-TRAXS) have been applied to X-ray chemical analysis of multilayered thin films on Si substrates. Clear differences were observed in the take-off angle (θ t) dependence of the X-ray intensities between Pd(10 nm)/Au(10 nm)/Si and Au(10 nm)/Pd(10 nm)/Si structures. The θ t dependence varied with layer thickness increase from 10 to 13 nm. An AlN(30 nm)/Al2O3(30 nm)/Si structure was also successfully analyzed by measuring the θ t dependence of NK α, OK α, AlK α and SiK α lines.
Investigation of Surface Passivation Effect of a-SiNx:H on a-Si:H by Photothermal Deflection Spectroscopy
Authors: Ikurou Umezu Ikurou Umezu , Michio Daigo Michio Daigo , Keiji Maeda Keiji Maeda
Published: October 2002

Optical absorption of surface- and interface-states in a-Si:H and a-SiN

x

:H (x=1.2 and 1.7) films was measured by photothermal deflection spectroscopy. The surface-state absorption of a-Si:H was reduced by passivation of the a-SiN1.7:H or a-SiN1.2:H layer. The surface absorptions of a-SiN1.7:H and a-SiN1.2:H are lower than that of a-Si:H. The origin of free surface absorption of a-Si:H was discussed in terms of the native oxide layer.
Carbon Phase Transition by Dynamic Shock Compression of a Copper/Graphite Powder Mixture
Authors: Günther Burkhard Günther Burkhard , Koji Dan Koji Dan , Yasuhiro Tanabe Yasuhiro Tanabe , Akira B. Sawaoka Akira B. Sawaoka , Kenjiro Yamada Kenjiro Yamada
Published: October 2002

Shock compression of a copper/graphite powder mixture was conducted. The shock - treated sample was characterized by micro - Raman spectroscopy and optical/electron microscopy. Cubic diamond in small quantities was detected. Synthesis of two cubic phases of carbon was determined by transmission electron microscopy (TEM). It was proposed that they originated via solid - vapor - solid (SVS) or solid - vapor - liquid - solid (SVLS) sequences of phase transformation. Copper may not merely be a coolant to rapidly quench the shock - loaded carbon, but also act as a physical and chemical reaction partner.
Plasma Parameters in Low-Pressure Ar–Hg Discharge Plasma Used for Liquid Crystal Display Back-Lighting
Authors: Goto Miki , Sakai Takayuki , Toshihiko Arai Toshihiko Arai
Published: October 2002

The electron temperature and electron density in the tube axis of a low-pressure Ar–Hg discharge lamp with 4 mm bore diameter have been measured under various bath temperatures with a probe method. Results show that the relative changes in the bath temperature dependence of electron temperature and electron density are similar to those obtained in the 36 mm I.D. discharge tubes. However, the electron temperature values are twice as large. The electron densities measured by the four methods used here are in good agreement with one another, indicating the reliability of the results.
Reverse-Mode Single Ion Beam Induced Charge (R-mode SIBIC) Imaging for the Test of Total Dose Effects in n-ch Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)
Authors: Koh Meishoku , Hara Ken-ichi , Horita Katsuyuki , Shigeta Bungo , Matsukawa Takashi , Kishida Atsushi , Tanii Takashi , Goto Makoto , Ohdomari Iwao
Published: October 2002

To achieve quantitative analysis of site-dependent total dose effects in metal-oxide-semiconductor field-effect transistors (MOSFETs), a new imaging technique designated as the reverse-mode single ion beam induced charge (R-mode SIBIC) imaging for sample positioning combined with accurate ion counting has been developed using the single-ion microprobe. With only five He single ions per pixel, we have succeeded in obtaining images of n-ch MOSFET and n-type Si regions fabricated on a p-well without any degradation of device characteristics. The R-mode SIBIC imaging has made it possible to count exactly the number of ions incident upon the MOSFET during radiation hardness tests.
Al-Reflow Process with a “Cap-Clamp” for Sub-Micron Contact Holes
Authors: Choi Gil-Heyun , Lee Sang-In , Park Chang-Soo , Park In-Seon , Ahn Sung-Tae , Kim Yong-Kil , Reynolds Reese
Published: October 2002

The use of “cap-clamp” has been demonstrated for extending the process margin of Al-reflow process. To evaluate the process window of Al-reflow with and without the “cap-clamp”, two major factors of in-situ annealing temperature and time were varied between 500-560° C and 40-90 seconds, respectively. Sub-micron contact holes were completely filled by heating wafers at 500° C or higher temperatures by adopting the “cap-clamp” to the conventional conduction heating system. The effect of the “cap-clamp” comes from the improved heating efficiency of the wafer by introducing hot Ar gas into the inner space of “cap-clamp”, resulting in faster ramp-up as well as more effective heating of the front-side of the wafer. Al-reflow with the “cap-clamp” gives wider process window than that of the conventional heating method and realizes the contact planarization of 256 Mbit dynamic random access memory (DRAM) and beyond.
NH3-Plasma-Nitridation Process of (100) GaAs Surface Observed by Angle-Dependent X-Ray Photoelectron Spectroscopy
Authors: Masuda Atsushi , Yonezawa Yasuto , Morimoto Akiharu , Tatsuo Shimizu Tatsuo Shimizu
Published: October 2002

X-ray photoelectron spectroscopy with varying the photoelectron take-off angle reveals the surface-nitridation process of (100) GaAs by an rf NH3 plasma with a magnetic field. The plasma treatment for shorter time or at lower temperature leads to the formation of a Ga-As-N ternary-compound layer on the GaAs surface. Increasing the treatment time or treatment temperature changes the main part of the surface layer into GaN due to the desorption of As. The oxidation resistance is also examined, showing that this plasma-nitridation method is one of the promising technologies for the passivation of (100) CaAs surface.
Plasma-Assisted MOCVD Growth of GaAs/GaN/GaAs Thin-Layer Structures by N-As Replacement Using N-Radicals
Authors: Michio Sato Michio Sato
Published: October 2002

GaAs/GaN/GaAs thin-layer structures were grown by plasma-assisted low-pressure metalorganic chemical vapor deposition. GaN layers were formed by exposing the surfaces of GaAs epitaxial layers to nitrogen-radical fluxes. When the nitrogen amount exceeded that in one-monolayer-thick GaN, the GaN/GaAs interfaces deteriorated drastically. Low-temperature photoluminescence from the structures suggests that the two-dimensional growth of GaN is limited to one-monolayer thick and that the excess nitrogen atoms form GaN clusters in the underlying layers. The one-monolayer-thick GaN embedded in GaAs shows intense photoluminescence, whereas the GaN cluster is non-radiative, probably because of the defects caused by the large lattice-mismatch between GaN and GaAs.
Growth Process in Initial Stage of GaAs/GaP(001) by Molecular Beam Epitaxy
Authors: Yoshikawa Masahiro , Nomura Takashi , Ishikawa Kenji , Minoru Hagino Minoru Hagino
Published: October 2002

The growth-mode transition of strained GaAs heteroepitaxial growth on GaP(001) is studied in detail using reflection high-energy electron diffraction (RHEED). The lattice parameter oscillation during layer-by-layer growth and the increase of the critical thickness of the growth-mode transition with increase of the growth rate reflect the elastic strain relaxation around the edge of two-dimensional nuclei and the existence of the kinetically controlled evolution of islands, respectively. The transformation from a strained metastable layer structure to a relaxed stable island structure is revealed through analyses of the RHEED pattern. We propose a model to explain the increase of the critical thickness, which assumes two processes at the surface, the formation of a metastable layer and its transformation to islands.
Fabrication of GaAs/AlGaAs Quantum Dots by Metalorganic Vapor Phase Epitaxy on Patterned GaAs Substrates
Authors: Junichi Motohisa Junichi Motohisa , Kazuhide Kumakura Kazuhide Kumakura , Motoya Kishida Motoya Kishida , Takahiro Yamazaki Takahiro Yamazaki , Takashi Fukui Takashi Fukui , Hideki Hasegawa Hideki Hasegawa , Kazumi Wada Kazumi Wada
Published: October 2002

We report on a growth process on patterned GaAs (001) substrate during metalorganic vapor-phase epitaxy (MOVPE) and a novel approach for the fabrication of AlGaAs/GaAs quantum dot (QD) structures. The patterned substrate has an array of holes on the surface and those holes are partially filled with GaAs by MOVPE growth, followed by GaAs/AlGaAs quantum well structures. Detailed investigation on the growth process on such patterned substrates revealed the presence of complicated two-dimensional duffusion of Ga and Al between two different surfaces. Formation of GaAs dots was directly confirmed by spatially resolved cathodoluminescence measurements.
In-Situ Surface Second-Harmonic Generation Study of Epitaxial Growth of GaAs
Authors: Yamada Chikashi , Takahiro Kimura Takahiro Kimura
Published: October 2002

Second-harmonic generation (SHG) observed in reflection from the growing surface of GaAs is reported. In a specific configuration of the polarization and crystal azimuths, only the surface specific component was observed. Combined with the reflection high-energy electron diffraction (RHEED) observation, we found that SHG is only sensitive to the chemical constituent on the surface while the RHEED is sensitive to long-range ordering of the surface reconstruction.
In Situ Mass Spectrometric Analysis of Surface Chemistry in MOMBE Growth
Authors: Sasaki Masahiro , Seikoh Yoshida Seikoh Yoshida
Published: October 2002

The surface chemistry in metalorganic molecular beam epitaxy (MOMBE) growth was studied by observing desorbed species with a mass spectrometer when differently prepared GaAs(100) surfaces were exposed to continuous and pulsed trimethylgallium (TMG) beams. It has been found that TMG decomposition is suppressed on oxidized GaAs surfaces (providing selective-area growth) and also on a GaAs surface having a stable structure (providing stoichiometry dependence of the growth rate). In this paper, we discuss the mechanism of these decomposition suppressions of TMG within the framework of precursor-mediated chemisorption. The suppression of decomposition on a mask surface is interpreted by considering the absence of the deep precursor states, while decomposition suppression on a GaAs surface with a stable structure was found to be due to a high barrier of the precursor states to chemisorption.
Characterization of Deep Levels in Si-Doped InxAl1-xAs Layers Grown by Molecular Beam Epitaxy
Authors: Malinin Alexei , Tomozawa Hidemasa , Hashizume Tamotsu , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

Deep levels in Si-doped InxAl1-xAs layers grown by molecular beam epitaxy were systematically investigated, changing the alloy composition for the first time. Deep level traps were characterized by deep level transient spectroscopy (DLTS) measurements and photoluminescence (PL) measurements. Two kinds of deep electron traps, E1 and E2 were observed. Least squares fitting curves of all data on the E1 and E2 traps were almost parallel to the Γ-band edge. From the observed dependence of trap level position on the alloy composition as well as from the comparison between DLTS and PL results, observed traps seem to be not DX center like donors but normal deep donors associated with the Γ-band.
Novel Surface Passivation Scheme for Compound Semiconductor Using Silicon Interface Control Layer and Its Application to Near-Surface Quantum Wells
Authors: Kodama Satoshi , Koyanagi Satoshi , Hashizume Tamotsu , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

A novel passivation scheme using an ultrathin molecular beam epitaxy (MBE) silicon interface control layer (ICL) and an ultrathin silicon nitride layer is investigated for use in the passivation of compound semiconductor quantum structures. Process optimization was performed by in-situ X-ray photoelectron spectroscopy (XPS) and electrical characterization of the insulator-semiconductor interface formed on In0.53Ga0.47As. A drastic reduction of interface state density into the 1010 cm-2·eV-1 range was obtained under optimum condition. The passivation scheme was then applied to passivation of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As near-surface quantum wells. Remarkable recovery of photoluminescence (PL) intensity was observed upon application of the present passivation scheme to the barrier surface, which was consistent with the reduction of surface states.
Effect of Phase Transformation Velocity on the Magnetic Domain Structure of YIG Single Crystal
Authors: Park Hyun Min , Park Bong Mo , Su Jin Chung Su Jin Chung
Published: October 2002

YIG single crystals were grown from a high temperature solution by top-seeded solution growth. The domain structure of grown crystals was investigated under a polarizing microscope. Magnetic domain patterns in a plate parallel to (110) face revealed a set of parallel-oriented, zig-zag curved, long stripes. The period of zig-zag curves depended on the cooling rates at the magnetic transition temperature, i.e. the velocity of transformation.
Highly Reproducible Fabrication Technology for Passivated AlGaAs/GaAs Heterojunction Bipolar Transistors with Pt/Ti/Pt/Au Base Electrodes
Authors: Hongo Sadato , Sugiyama Tohru , Kuriyama Yasuhiko , Iizuka Norio , Masao Obara Masao Obara
Published: October 2002

A highly reproducible fabrication technology for passivated heterojunction bipolar transistors (HBT's) has been developed. A thermally stable Pt/Ti/Pt/Au base electrode metal penetrates through the Al0.3Ga0.7As emitter layer to contact the base layer. This feature leads to the formation of the base passivation layer. A citric-acid-based selective etchant eliminates the ambiguity of etching and thus confirms the reproducibility of passivation layer thickness. The excess base leakage current density was reduced to about 1 µ A/µ m.
Control of As Precipitation in Low-Temperature GaAs by Electronic and Isoelectronic Delta Doping
Authors: Cheng Tzyy Ming , Chang Chun Yen , Huang Jin Hua
Published: October 2002

A systematic study of electronic (Si and Be) and isoelectronic (In and Al) delta-doping effects on the formation of arsenic precipitates in GaAs grown by molecular beam epitaxy (MBE) at low substrate temperature is presented. Both electronic dopant Si and isoelectronic dopant In are found to accumulate As precipitates in postgrowth-annealed samples, while the precipitate accumulation effect is more prominent for Si than In. As precipitate is depleted from regions doped with Be or Al. The results suggest that the electronic property of impurity does not have a direct correlation with the As precipitation process. The effects of doping concentration and postgrowth annealing temperatures are also reported. The ability to control the As precipitates in low-temperature materials should lead to a wide variety of device applications.
InGaP/GaAs Heterojunction Bipolar Transistors with an Ultra-High Carbon-Doped Base (p=1.5×1021cm-3)
Authors: Shirakashi Jun-ichi , Azuma Toshiaki , Fukuchi Fumihiko , Konagai Makoto , Takahashi Kiyoshi
Published: October 2002

In0.5Ga0.5P/GaAs heterojunction bipolar transistors (HBTs) having a heavily carbon (C)-doped GaAs base with an ultra-high hole concentration of 1.5×1021 cm-3 were successfully fabricated by metalorganic molecular beam epitaxy (MOMBE) for the first time. Tertiarybutylphosphine (TBP), elemental In and elemental Ga were used as source materials for the growth of In0.5Ga0.5P emitter and trimethylgallium (TMG) and elemental arsenic ( As4) for the growth of GaAs base. Abrupt change of composition was obtained at the heterointerface between InGaP emitter and heavily C-doped GaAs base, suggesting no defect formation due to heavy doping in the base. Small signal current gain (h
fe) of 16 and DC current gain (h
FE) of 12 were obtained for devices with a base thickness of 15 nm despite the ultra-high doping in the base layer. To our knowledge, this is the first report on the InGaP/GaAs HBTs with an ultra-high C-doped base layer.
Novel Wire Transistor Structure with In-Plane Gate Using Direct Schottky Contacts to 2DEG
Authors: Hiroshi Okada Hiroshi Okada , Kei-ichiroh Jinushi Kei-ichiroh Jinushi , Nan-Jian Wu Nan-Jian Wu , Tamotsu Hashizume Tamotsu Hashizume , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

A novel wire transistor structure with Schottky in-plane gates (IPG) to the AlGaAs/GaAs quantum well (QW) has been successfully fabricated and characterized. An in situ selective electrochemical process is utilized to form direct Schottky contacts to the edge of the QW. Details of the novel process for transistor fabrication, as well as field-effect characteristics of the novel device, are presented and discussed. Field-effect transistor (FET) characteristics with excellent gate control and clear pinch-off are obtained at room temperature and they are compared with a theory newly developed for the IPG FET.
Dynamic Characteristics of Inverter Circuits Using Single Electron Transistors
Authors: Yoshikawa Nobuyuki , Ishibashi Hiroshi , Masanori Sugahara Masanori Sugahara
Published: October 2002

We have investigated the basic characteristics of capacitively and resistively coupled single-electron tunneling (SET) inverters as a digital logic circuit. Static and dynamic characteristics have been calculated based on the semiclassical model using the Monte Carlo method. Although a voltage gain larger than unity is found even in a cascade connection of two stages of the SET inverters, they reveal some disadvantages in digital logic application, such as small voltage gain, poor input-output separation, small logic level difference, instability of operating point and oscillating output voltages. The switching delay time is estimated to be on the order of 100R
C, where R and C is resistance and capacitance of a tunnel junction, respectively. The stability of logic voltage levels has also been verified in cross-coupled latch circuits.
Composition Modulation in Quantum Wire Structures on Vicinal (110) GaAs Studied by Photoluminescence
Authors: Koichi Inoue Koichi Inoue , Hu Kun Huang Hu Kun Huang , Misaichi Takeuchi Misaichi Takeuchi , Kenta Kimura Kenta Kimura , Hisao Nakashima Hisao Nakashima , Masaaki Iwane Masaaki Iwane , Osamu Matsuda Osamu Matsuda , Kazuo Murase Kazuo Murase
Published: October 2002

Quantum wires are fabricated by the growth of the AlGaAs system on vicinal (110) GaAs substrates misoriented toward (111)A. It is concluded that during the growth of AlGaAs, composition modulation occurs on the large-step structure almost independently of the temperature, while the large-step structure is formed by the growth only below a transition temperature. The photoluminescence (PL) from a single quantum wire is observed with a much narrower spectral width as compared with the PL from multi-quantum wires.
Evaluation of Thin Silicon Dioxide Layers by Beam Assisted Scanning Tunneling Microscope
Authors: Heike Seiji , Wada Yasuo , Kondo Seiichi , Lutwyche Mark , Murayama Ken , Hiroshi Kuroda Hiroshi Kuroda
Published: October 2002

The electronic structure of thin thermal silicon dioxide ( SiO2) layers are evaluated by beam assisted scanning tunneling microscope (BASTM). The BASTM operation principle is that an insulator sample is exposed with an electron beam, which excites electron-hole pairs in the insulator and makes the sample conductive. 100 nm wide line and space patterns are delineated by electron beam lithography and dry etching in a 10 nm thick thermally grown silicon dioxide layer, and are observed by BASTM to ascertain the capability. Current-voltage (I-V) characteristics are measured for silicon dioxide layers with thicknesses between 1.8 and 4.5 nm by tunneling spectroscopy. The results indicate that both the band gap and barrier height have no dependence on the silicon dioxide layer thicknesses.
Superconducting Three-Terminal Devices Using an InAs-Based Two-Dimensional Electron Gas
Authors: Takayanagi Hideaki , Akazaki Tatsushi , Nitta Junsaku , Enoki Takatomo
Published: October 2002

A newly fabricated three-terminal Josephson junction is coupled with an InAs-inserted-channel InAlAs/InGaAs heterostructure. The two-dimensional electron gas (2DEG) confined in the inserted InAs layer has a high mobility of 73800 cm2/V·s and a high sheet-carrier density of 1.98×1012 cm-2 at 4.2 K.
The supercurrent flows through the 2DEG and can be controlled by gate voltage. The critical current and the normal resistance as a function of gate voltage are measured and the sheet-carrier density dependence of the critical current is obtained. The experimental results for this dependence are explained by the superconducting proximity effect theory and by the normal transport of the 2DEG.
Water-Immersion-Induced Surface Reactions of EuBa2Cu3Oy Thin Films
Authors: Kiyokura Takanori , Maeda Fumihiko , Watanabe Yoshio , Oshima Masaharu , Asano Hidehumi , Minoru Suzuki Minoru Suzuki
Published: October 2002

Photoelectron spectroscopy was performed on EuBa2Cu3O

y

thin films before and after immersion into de-ionized pure water to clarify the water immersion effect on copper oxide superconductors during water rinsing in device fabrication. The surface Ba compounds were found to drastically decrease, while a short (5 minutes) water immersion of epitaxial-quality thin films barely affected bulk EuBa2Cu3O

y

.
AC Conduction Mechanism in Borate Glasses Containing Antimony and Arsenic Ions
Authors: Datta A. , Giri A. K. , D. Chakravorty D. Chakravorty
Published: October 2002

AC resistivities of borate glasses containing pentavalent antimony or arsenic ions of a maximum fraction of 0.3 have been measured over the temperature range 90 to 350 K. A sharp minimum in resistivity is observed for all the samples at a temperature around 315 K. The ac resistivity variation at temperatures lower than 290 K can be explained on the basis of overlapping large polaron tunnelling (OLPT) mechanism.
Effects of F+ Implantation on the Characteristics of Poly-Si Films and Low-Temperature n-ch Poly-Si Thin-Film Transistors
Authors: Park Jin Won , Ahn Byung Tae , Lee Kwyro
Published: October 2002

Fluorine was implanted onto poly-Si films through an oxide layer and its passivation effect on poly-Si films and low-temperature n-ch TFTs was investigated. The implant energy of F+ ions was 40 keV, and the F+ dose was varied from 5×1012 to 4×1015 cm-2. The fluorine implanted inside poly-Si film preferentially diffused toward the poly- Si/SiO2 interface during annealing at 600° C. The residual implant damage was found to remain inside poly-Si films after annealing at 600° C when the F+ dose was ≥5×1014 cm-2. The resistivity and activation energy of the p-type poly-Si resistors were increased as the F+ dose increased, resulting from the increase of residual implant damage. However, the characteristics of the n-ch poly-Si TFT were clearly improved when the F+ dose was in the range of 5×1014 to 2×1015 cm-2, where the trap state density at the poly Si/SiO2 interface was found to be reduced because of the passivation effect by fluorine atoms. These results indicated that the fluorine passivation at the poly- Si/SiO2 interface was effective in an appropriate F+ dose range, while the passivation inside the poly-Si film (or grain boundary passivation) was not.
Electrical Properties of Layered ZrSe2Single Crystals Annealed in Selenium Atmosphere
Authors: Tetsuo Ikari Tetsuo Ikari , Kouji Maeda Kouji Maeda , Koji Futagami Koji Futagami , Akio Nakashima Akio Nakashima
Published: October 2002

Temperature dependencies of electron carrier concentrationnand Hall mobility µHof layer ZrSe2single crystals are investigated for samples annealed in vacuum or Se atmosphere. The high carrier concentration in the order of 1019 cm-3for the as-grown sample decreases to 1018 cm-3upon annealing in Se atmosphere. We consider that the dominant donor state in ZrSe2is produced by a complex involving interstitial Zr atoms and Se vacancies. The temperature dependence of µHis explained by inter and intravalley electron scattering by acoustic phonons.
The Damage Energy Transfer to Interfacial Oxide by Phosphorus Ion Implantation for Small Geometry Polysilicon to Polysilicon Contact
Authors: Shibata Hideki , Kazuhiko Hashimoto Kazuhiko Hashimoto
Published: October 2002

The characteristics for small geometry polysilicon to polysilicon contact were investigated focusing on the damage energy transfered to an interfacial oxide by phosphorus ion implantation. The damage energy distribution were estimated based on Brice's model, and the relationship between the damage energy and the contact resistance was discussed. It was found that although the contact resistance decreases with increasing the damage energy, the impurity concentration at the contact interface is also significant for reduction of the contact resistance. Moreover, two kinds of models were proposed to explain the conduction mechanism. One is a filament model, the other is a direct tunneling model. Furthermore, an appropriate ion implanted condition to minimize the contact resistance was presented. It was confirmed that the projection range of phosphorus ions has to be set to be 50 Å shallower than the distance to the contact interface.
Relation between Stress-Induced Leakage Current and Dielectric Breakdown in SiN-Based Antifuses
Authors: Hiroaki Yasuda Hiroaki Yasuda , Naoki Ikeda Naoki Ikeda , Kaoru Hama Kaoru Hama , Mariko T. Takagi Mariko T. Takagi , Ichiro Yoshii Ichiro Yoshii
Published: October 2002

We report on the degradation process of metal-to-metal antifuses that use thin silicon nitride film as the dielectric layer under high electric field stress. Stress-induced leakage current was observed in all samples, and it flows through local spots. Two-level fluctuations were found on the leakage current well below the stress voltage, and large and complex fluctuations were observed near the stress voltage. The conduction mechanism of the stress-induced leakage current was the Poole-Frenkel type. It was found that the dielectric constant of the path became large and that the breakdown and the anomalous current depended on the barrier metal thickness. Considering these results, the stress-induced leakage current and the breakdown are thought to be caused by electromigration of electrode material to the SiN film.
Chemical Reaction of Sb Atoms in Si Melt
Authors: Huang Xinming , Terashima Kazutaka , Izunome Koji , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

The oxygen solubilities in undoped and Sb-doped Si melts have been investigated after quenching. It was found that the oxygen solubility increased with increasing Sb concentration in the Si melt, and the increased oxygen concentration was proportional to the square of the Sb concentration in the Si melt. To explain the phenomenon we suggest that some ordering of Sb2O existed in the Sb-doped Si melt. The equilibrium constant for the reaction forming Sb2O in the Sb-doped Si melt was determined to be 6300. It was calculated using the equilibrium constant that the portion of the Sb2O in the Sb-doped Si melt increased with increase in Sb concentration and/or oxygen concentration in the Si melt.
Strain-Compensated Multi-Quantum Barriers for Reduction of Electron Leakages in Long-Wavelength Semiconductor Lasers
Authors: Loh Terhoe , Miyamoto Tomoyuki , Koyama Fumio , Kenichi Iga Kenichi Iga
Published: October 2002

To suppress the leakage of hot electrons and thermionic electrons over the hetero-barrier of an active layer for long-wavelength lasers, we have proposed a two-cavity strain-compensated multi-quantum barrier, which utilizes alternate strain natures in wells and barriers to increase the barrier height. The coupling of two strain-compensated superlattices under the off-resonant condition increases the virtual electron barrier up to about 1.3 eV.
It is not only sufficient to suppress the hot electrons, but it has the advantages of aluminium-free crystal growth and suppression of misfit dislocations by strain-compensation.
Microstructure and Phase-Transformation Studies of Cu-Ni-Sn Alloys
Authors: Pal Hiranmay , Pradhan Swapan Kumar , Madhusudan De Madhusudan De
Published: October 2002

Six compositions of Cu-Ni-Sn alloys in the α and (α+θ) phase containing 2.7 to 13 wt% Sn and 5 to 22 wt% Ni have been prepared for structure-property correlation by X-ray diffraction, optical and scanning electron microscopy, microhardness and ageing studies. X-ray diffraction line profile analysis characterizes the plastically deformed state of the homogenised α-matrix through the evaluation of different defect parameters. The results reveal that the α-matrix is more prone to faulting and the solute Sn predominantly controls the defect state. With increasing solute concentration the matrix becomes slightly depleted of Sn and Ni resulting in some lowering in the lattice parameter values. The decomposition process has been investigated by ageing study on prior cold-worked (hand-filed) samples and the precipitating phases identified as 2H, DO3and DO19along with α-phase with varying Sn and Ni concentrations. However, no evidence of spinodal decomposition has been noticed. From optical microscopy and energy dispersive X-ray (EDX) study grain boundary precipitation having composition (CuxNi1-x)3Sn has been detected in higher Sn content alloys and the composite matrix reveals a dendritic structure in the micrographs. Microhardness study of homogenised alloy shows considerable increase in the microhardness values for high Sn content alloys undergoing precipitation. Unlike deformed alloys in the form of filings, deformed (compressed) bulk samples are found to be less prone to decomposition on ageing as revealed from X-ray and microhardness studies.
Characteristics of Surface Acoustic Waves on Proton-Exchanged and Annealed Proton-Exchanged Z-Cut LiNbO3 Using Pyrophosphoric Acid
Authors: Cheng Chien-Chuan , Chen Ying-Chung , Wang Sheng-Tz , Bo-Wen Tsai Bo-Wen Tsai
Published: October 2002

The characteristics of surface acoustic waves (SAWs) on proton-exchanged (PE) and annealed proton-exchanged (APE) Z-cut Y-propagated LiNbO3 waveguides using pure pyrophosphoric acid are investigated and compared. The distribution of hydrogen in the PE samples measured by secondary-ion mass spectrometry (SIMS) shows a step-like profile with the diffusion constant D
0 and the activation energy Q of about 9×107 µ m2/ h and 82.18 kJ/mol, respectively. The velocity (V
p) of SAW on PE samples decreases with the increase of k
d, where k is 2π/λ and d is the waveguide depth, and almost exhibits an exponential decay. However, post-annealing will result in a restoration of the decreased velocity and an improvement of the SAW insertion loss (IL). On the other hand, the electromechanical coupling coefficient (K
2) almost decreases with the increase of k
d and shows greater sample-to-sample discrepancy.
Electron Spectroscopy for Chemical Analysis Study on Influence of Polymerization on Anisotropic Etching of Thick Silicon Oxide Using C 2F 6 Based ECR-RIBE
Authors: Achyut Kumar Dutta Achyut Kumar Dutta
Published: October 2002

Anisotropic etching mechanism is investigated increasing the CF2 precursor in C2F6 plasma. The increasing of CF2 precursor is known from the ESCA (electron spectroscopy for chemical analysis) measurement of C/F elemental ratio of the deposited layer. It is found that the C/F ratio is increased from 0.28 to close to 1, when the microwave power of plasma is increased from 150 W to 350 W, respectively. The side wall angle of the deep SiO2 etching under the power of 350 W, is found to be close to 90°. The SiO2 etching selectivity with respect to the chromium (Cr) metal mask is also found to be enhanced considerably with the increasing of microwave power.
Optical Emission Analysis of Triple-Fold Plume Formed at Pulsed IR Laser Ablation of Graphite
Authors: Tasaka Yoshiharu , Tanaka Masatoshi , Seiji Usami Seiji Usami
Published: October 2002

A sheet of sintered graphite was ablated by a pulsed Nd:YAG laser in He gas and air at 1 atm. Triple-fold plumes were produced in both gases. The time-resolved emission spectrograms of the plume were measured and the plume was analyzed as follows. The plume is generated near the target surface and expands while separating into three because of different expansion speeds of its components. The fastest component is gas plasma mainly composed of carbon ions in the He atmosphere, and nitrogen and oxygen ions in air. The second fastest component is very hot and compressed neutral molecules of the gas, that is, the shock wave. The slowest component is radical vapor of the graphite target.