bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-Temperature Pulsed Operation of GaInNAs Laser Diodes with Excellent High-Temperature Performance
Authors: Kondow Masahiko , Nakatsuka Shin'ichi , Kitatani Takeshi , Yazawa Yoshiaki , Okai Makoto
Published: October 2002

We have successfully operated GaInNAs laser diodes with a pulsed current at room temperature. The lowest threshold current density was about 0.8 kA/cm2, and the lasing wavelength was about 1.2 µ m. Characteristic parameters such as internal quantum efficiency and the gain constant were measured, and excellent high-temperature performance was observed. The characteristic temperature was 127 K in the temperature range from 25 to 85° C.
Measurements of Time Delays in Superradiant Laser Emssions from Binary Dye Mixtures
Authors: Yap Yeeping , Teckyong Tou Teckyong Tou , Kuanhiang Kwek Kuanhiang Kwek
Published: October 2002

The concentration dependence of the time delays, in the range of 80–800 ps, between two-color superradiant laser emissions from three enthanol solutions of the binary dye mixtures, C460/DF, DF/R640, and C460/R640, which were excited using a 1 ns transversely excited atmospheric (TEA) N2 laser was measured by a fast streak camera. While these time delays confirmed that radiative laser energy transfer as the predominant mechanism for multicolor laser emission from a single dye-mixture solution, these emissions were not usually obtained simultaneously, even when a broadband optical resonator was used.
Luminescent Characteristics of ZnGa2O4:Mn Phosphor Thin Films Grown by Radio-Frequency Magnetron Sputtering
Authors: Yu Chang Feng , Lin Pang
Published: October 2002

Mn-doped ZnGa2O4 phosphor thin films on Si(100) were prepared by rf sputtering at 500° C. Under UV light excitation, the deposited films showed a green emission band with a peak at 508 nm. Monitored at 508 nm, the excitation spectrum of the films showed a primary absorption at 245 nm. The spectra were similar to those of zinc gallate powder but with a larger band width. The films exhibited a high resistivity whether or not under the UV excitation. The possible energy transfer processes occurring in the material were discussed, and the resonance process was considered the dominant mechanism. From the spectral transmittance of undoped zinc gallate films sputtered on quartz glass, the evaluated indirect-transition optical gap was found to be 4.25 eV. The absorption by Ga3+ ions at 245 nm in the excitation spectrum was identified with the band-to-band transition of ZnGa2O4 host lattice.
Stabilization of Photoluminescence of Porous Silicon with Nonaqueous Anodic Oxidation
Authors: Shimura Michiko , Minoru Katsuma Minoru Katsuma , Tsugunori Okumura Tsugunori Okumura
Published: October 2002

In order to prevent the reduction of photoluminescence from porous silicon, we tried to form stable Si–O bonds by anodization in nonaqueous electrolyte at room temperature. Extremely strong, stable, and blue-shifted photoluminescence was obtained in porous silicon that was prepared in 1:1 solution of 49% HF and EtOH and subsequently anodized in KNO3-ethylene glycol electrolytes. The optimum condition was anodization at 20 mA cm-2 for 5 min in 0.02 M KNO3-ethylene glycol. For the formation of Si–O bonds on nanostructured surfaces, it is suggested that the electric field across the surface/electrolyte plays an important role because oxidation becomes more effective when the electrolyte is more resistive. Si–OH, which is formed as a precursor at subsequent anodization, stabilizes the nanostructured surface, converting itself to more stable Si–O bond with photoexcitation. The high current density introduced destroys nanostructured silicon by clustering with surrounding SiO2. With this clustering, wall sizes of the nanostructured silicon remain constant with anodization.
Analysis of Current-Voltage Characteristics of Organic Electroluminescent Devices on the Basis of Schottky Emission Mechanism
Authors: Matsumura Michio , Jinde Yukitoshi , Tomonori Akai Tomonori Akai , Takashi Kimura Takashi Kimura
Published: October 2002

The mechanism of hole injection from the indium-tin-oxide (ITO) electrode into the hole-transporting layer of the organic electroluminescent (EL) device was concluded to be Schottky emission. The barrier height at the ITO/hole-transporting layer interface was determined to be about 0.39 eV and the field-free current density to be 7.1 ×10-2 Am-2 at room temperature. From the analysis of the current–voltage (I–V) characteristics of the organic EL devices on the basis of the carrier injection mechanisms, we found that the currents of the organic EL devices having the organic bilayer structure are governed by the properties of carrier injection from the electrodes. Important information on the potential distribution in the organic layers and the effective dielectric constant for the carrier injection processes were also acquired from the comparison of the I–V curves with the theoretical calculations.
Electrical and Microstructural Degradation with Decreasing Thickness of (Ba, Sr)TiO3 Thin Films Deposited by RF Magnetron Sputtering
Authors: Paek Su-Hyon , Won Jinhee , Lee Kong-Soo , Choi Jin-Seog , Park Chi-Sun
Published: October 2002

The electrical degradation of (Ba, Sr)TiO3 [BST] thin films as a function of the film thickness was investigated. BST thin films with various thickness were deposited on Pt/Ti/SiO2/Si substrates by in-situ RF magnetron sputtering. It was found that the electrical properties degraded markedly as the thickness of the films decreased. Electrical properties such as the leakage current and the dielectric constant are closely related to the surface morphology, in particular, the grain size of the films. The existence of an interfacial layer between the BST film and the Pt bottom electrode was confirmed by HRTEM. The interfacial layer appeared to have crystallinity different from both the BST thin film and the Pt bottom electrode which resulted in variation of the interfacial states between BST and Pt. As the thickness of the BST films decreased from 300 nm to 50 nm, the thickness of the interfacial layer increased from 9.5 nm to 11 nm. The dielectric constant of the interfacial layer calculated from its measured overall capacitance and thickness, confirmed by HRTEM, was about 30. This low-dielectric-constant interfacial layer has been shown to affect the electrical degradation of BST thin films with decreasing thickness.
Piezoelectric Properties of Nylon 79 Thin Films Prepared by Vapor Deposition Polymerization
Authors: Hattori Takeshi , Takahashi Yoshikazu , Masayuki Iijima Masayuki Iijima , Eiichi Fukada Eiichi Fukada
Published: October 2002

Thin films of nylon 79 were prepared by vapor deposition polymerization of 1,7-diaminoheptane and azelaic acid chloride. Preliminary values for the piezoelectric stress constant, e
31 (= 2 mC/m2), and the pyroelectric constant, p
3 (= 2 mC/m2 K), were obtained for poled films. Three relaxation processes in the temperature dependence of the dielectric constant ε
3 were observed at -130° C (γ), -50° C (β), and 70° C (α) similar to those for nylon 7 and 11 and aliphatic polyureas. The piezoelectric constant e
31 remained up to about 130° C.
Performance of Conventional and Novel Deformed Helix Ferroelectric Liquid Crystal Display Operating Modes
Authors: Jürg Fünfschilling Jürg Fünfschilling , Martin Schadt Martin Schadt
Published: October 2002

Fast response times and wide viewing angles are characteristic features of the deformed-helix ferroelectric liquid crystal displays (DHF-LCDs) presented in this paper. We first discuss the electrooptics of the DHF effect, emphasizing the large electrically induced changes of birefringence which occur in DHF-LCDs with large switching angles. Based on these results a new DHF operating mode is introduced, which allows DHF display cell gaps larger than 5 µm. A second new type of DHF-LCD operating mode is then presented, which is used for low-tilt-angle DHF materials. This second, double-layer DHF-LCD allows fast, bright, ghost-free, low-voltage operation. Finally, the influence of various FLC material parameters and their temperature dependence on DHF display performance is investigated. It is shown that a pitch below 150 nm at room temperature is required for high-contrast DHF-LCDs. It is also shown that with suitable driving electronics, operation of DHF-LCDs at video rates is possible down to -15°C.
Preparation and Electrical Properties of Sintered Bodies Composed of Monophase Spinel Mn(2-X)Co2XNi(1-X)O4 ( 0 \LeqX \Leq 1) Derived from Rock-Salt-Type Oxides
Authors: Yokoyama Takashi , Abe Yoshiaki , Meguro Takeshi , Komeya Katsutoshi , Kondo Kazuyuki , Sasamoto Shinobu Kaneko
Published: October 2002

Preparation of spinel-type oxides, Mn(2-
X
)Co2
X

Ni(1-
X
)O4 (0≦X≦1), and their electrical properties were investigated. Die-pressed oxides (25 mm diam. ×4 mm), containing metals with desired molar ratios, were heated to 1400° C, and held at that temperature for 3 h in nitrogen. The sintered specimens were quenched to 800° C and then oxidized for 95 h in air to completely convert them into spinel-type oxides. The lattice constants of the spinels decreased with increasing X. Two turning points, at X=0.5 and 0.84, were observed. Based on these results, the cation distributions were estimated. Calculation of the Seebeck coefficient proved that the carriers of the oxides with X=0 and 0.25 are electrons and those of the oxides with X=0.5 to 1 are holes. Activation energies calculated from mobility were 0.34 to 0.36 eV. The conduction was considered to be due to the small polaron hopping mechanism.
Antenna Charging Effects on the Electrical Characteristics of Polysilicon Gate during Electron Cyclotron Resonance Etching
Authors: Kang Tzong-Kuei , Ueng Shih-Yuan , Dai Bau-Tong , Chen Liang-Po , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

The nonuniformity of the induced leakage current in metal oxide semiconductor (MOS) capacitors has been investigated in an electron cyclotron resonance (ECR) system. For plasma-etched MOS capacitors with 5-nm-thick oxides, it is found that the leakage currents induced by plasma etching increase with increasing overetching time. However, additional E
bd (breakdown field) degradation is not obvious as overetching percentage increases from 10% to 50%. A mechanism based on the antenna charging effect has been proposed to explain the E
bd electrical characteristics. In accordance with the mechanism, the E
bd degradation has been significantly reduced by first etching off a narrow peripheral edge around the gate pattern.
Effects of the Annealing in Ar and H2/Ar Ambients on the Microstructure and the Electrical Resistivity of the Copper Film Prepared by Chemical Vapor Deposition
Authors: Rha Sa-Kyun , Lee Won-Jun , Lee Seung-Yun , Kim Dong-Won , Chong-Ook Park Chong-Ook Park , Soung-Soon Chun Soung-Soon Chun
Published: October 2002

The copper films with a thickness of 600 nm were prepared on TiN at 180° C under 0.5 Torr using chemical vapor deposition (CVD) method. The deposited films were subjected to be annealed at various temperatures (350–550° C) in Ar and H2(10%)/Ar ambients. The changes of the microstructures and the electrical resistivity after annealing were investigated. H2(10%)/Ar was more effective than Ar as an ambient gas for the post annealing of the copper films, because smaller resistivity and larger grain size of the annealed film was given. The resistivity of the annealed film decreased, and the grain size increased with the annealing temperature. However, 550° C is found to be inappropriate as the annealing temperature, because the out-diffusion of silicon through the TiN layer was observed. Upon annealing at 450° C for 30 min in an H2(10%)/Ar ambient, the grain size of the film increased from 148 nm to 219 nm, and the resistivity decreased from 2.35 µ Ω·cm to 2.12 µ Ω·cm.
Microhardness and Strain Depth Profiles in Nitrogen-Implanted TiO2 Films
Authors: Yamada Kazunori Fukushima
Published: October 2002

Microhardness and strain depth profiles of N+-implanted epitaxial rutile TiO2 films on sapphire were studied. Implantation profiles were elucidated by sputtering beveled samples (inclination: 200–300 nm/10 mm), thereby facilitating depth profiling in which the analyzing probe was shifted to different depths on the sample surface. In a 180-keV-implanted sample, microhardness and interplanar spacing of the lattice increased with increasing depth, corresponding to the increase in defect density. Within the amorphized damage peak region, the microhardness was found to be lower than that in the crystalline region. In a multienergy-implanted sample (10, 40, 90 keV), a TiO2 phase transformation from rutile to anatase was observed. We found that defect-induced and atom-incorporation-induced stress and strain exerted a strong influence on the microhardness and microstructure of the films.
Growth and Characterization of CeO2Films on Sapphire Substrates by Sputtering Process
Authors: Lin Ran-Jin , Chen Lih-Juann , Lin Lih-Jiaun , Yu Yueh-Chung , Wang Chang-Wan , Lin Erh-Kang
Published: October 2002

Two-inch-diameter CeO2films on R-plane (1*BAR*1*BAR*02) sapphire substrates have been prepared using an on-axis rf magnetron sputtering method. The effects of postannealing treatment, sputtering gas pressure and substrate temperature on the orientation, crystallinity and surface morphology of the CeO2films have been investigated. The (100)-preferred CeO2films with high crystallinity are grown at 820° C and 0.15 Torr and have a full width at half-maximum value of the rocking curve of (200) planes of 0.15°. The spatial variation of thickness of the CeO2films across the 2-inch substrate is about 5.8%. Thec-axis oriented YBa2Cu3Ox(YBCO) films grown on sapphire substrates with a (100)-preferred CeO2buffer layer of 100 nm are made. The YBCO films have superconducting properties with theTcbeing 88–90 K andJc(77 K, 0 T) being (1–3)×106A/cm2.
Stability of Densely Contact-Electrified Charges on Thin Silicon Oxide in Air
Authors: Morita Seizo , Uchihashi Takayuki , Okusako Takahiro , Yamanishi Yoshiki , Oasa Takahiko , Yasuhiro Sugawara Yasuhiro Sugawara
Published: October 2002

By changing the polarity of charged trap sites, we investigated the stability of densely contact-electrified charges on thin silicon oxide in air using a modified atomic force microscope. For usual silicon oxides with positively charged trap sites, a stable state is obtained only for negative charge deposition, while for modified silicon oxides with negatively charged trap sites, a stable state is obtained only for positive charge deposition. As a result, we concluded that charged trap sites make densely contact-electrified charges with the same polarity unstable due to the strong Coulomb repulsive force.
Auger Electron and X-Ray Photoelectron Spectroscopy Studies of Oxidation of Tin Using SnOx Thin Films Grown by Reactive Ion-Assisted Deposition
Authors: Choi Won-Kook , Cho Jun-Sik , Song Seok-Kyun , Hyung-Jin Jung Hyung-Jin Jung , Seok-Keun Koh Seok-Keun Koh
Published: October 2002

In order to accurately determine the oxidation state of tin and to investigate the chemical shifts between tin and its oxides, quantitative Auger electron spectroscopy and X-ray photoelectron spectroscopy studies were performed using Sn metal, stoichiometric SnO2 powder, and polycrystalline SnO

x

thin films. Films with different oxygen contents were grown using a reactive ion-assisted deposition technique. As the atomic ratio of tin to oxygen in the deposited films increased to the stoichiometric value of 2, the tin M
4
N
4,5
N
4,5 Auger transition and the corresponding Sn 3d
5/2 core-level photoelectron line gradually shifted to lower kinetic energy and higher binding energy by as much as 6±1 eV and 2.39±0.02 eV, respectively, relative to those of the tin metal. An explanation for the observed systematic difference between the chemical shifts of Auger and photoelectron lines is given. It is based on the difference in electronic polarization energy between the final two-hole state produced by the Auger electron emission and the final single-hole state produced by the photoelectron emission.
X-Ray Diffraction study of Langmuir-Blodgett Films of Mn-Arachidate
Authors: Takamura Takumi , Matsushita Ken , Shimoyama Yuhei
Published: October 2002

To elucidate the structure of organic thin films having magnetic properties, we performed X-ray diffraction, differential scanning calorimetry and electron paramagnetic resonance measurements on the Langmuir-Blodgett (LB) films of Mn-arachidate. The LB films of Mn-arachidate were found the most feasible system for the study of magnetic thin films due to their reproducibility. We found that orientation of the fatty acid molecules correlates with the number of layers or thickness of films; films having less than three layers show the perpendicular orientation of fatty acid molecules to the substrate surface. However, films of more than five layers exhibit the tilt orientation with respect to the layer normal. The tilt angle increases with the thickness of the LB films. Homogeneous distributions of the crystalline size were found in the LB films.
An Approach to Fit Ion Induced Secondary Electron Emission Coefficient on Ion Energy in Some Insulators
Authors: Khairi I. Grais Khairi I. Grais , M. L. Marcos M. L. Marcos
Published: October 2002

No theory exists explaining the kinetic emission of the ion induced secondary electron emission containing physical parameters of the emitter. Dionne derived an equation for the secondary electron emission yield based on no scattering and on a constant energy loss. Khairi et al.., split Dionne's equation into the production and the emission terms. Recently, Rajopadhye et al.. considered both terms to remain the same as in secondary electron emission replacing the constant loss energy and the range of the primary electron by those corresponding for the primary ions. In the present approach, equations other than those used by Rajopadhye et al.. have been chosen to describe the low energy range of induced secondary yield. The mean free path λ s and the energy required to excite a secondary ξ are largely energy dependent. λ s is given empirically as a function of the primary energy.
Alternating Conductivity in a Weakly Relativistic Gas Plasma
Authors: Mitsuaki Nagata Mitsuaki Nagata
Published: October 2002

Characteristics of alternating conductivity in a weakly relativistic gas plasma are investigated based on the relativistic equation for the electron drift velocity, and the existence of negative conductivity, which leads to the amplification of an electromagnetic wave, in a slightly ionized, tenuous gas plasma is reported.
Thermal Desorption Spectroscopy of Alkanethiol Self-Assembled Monolayer on Au(111)
Authors: Nishida Naoki , Hara Masahiko , Hiroyuki Sasabe Hiroyuki Sasabe , Wolfgang Knoll Wolfgang Knoll
Published: October 2002

The adsorption and desorption of octadecanethiol ( CH3(CH2)17SH: monomer) self-assembled monolayers (SAMs) on Au(111) have been investigated by thermal desorption spectroscopy (TDS). Two desorption peaks of dioctadecyl disulfide ( (CH3(CH2)17S)2
+: dimer+) exhibiting different sticking behaviors have been identified in the TDS spectra, while the desorption of octadecanethiol ( CH3(CH2)17SH+: monomer+) occurred at a lower temperature than that of the dimer+. The desorption activation energy and the pre-exponential factor for each peak were estimated assuming first- and second-order reactions. The analysis results suggest that both alkyl thiolate (RS–Au) with strong chemisorption and dialkyl disulfide (RS–SR: dimer) with relatively weak adsorption co-exist in the alkanethiol SAM on Au. The total amount of relatively weakly adsorbed dimers increased appreciably in a slow reaction step, while the monolayer thickness remained almost constant after SAM formation. This result suggests that dimer molecules are formed in the monolayer. This formation of weakly adsorbed dimers is strongly related to the self-exchange phenomena in SAM films reported by Schlenoff et al.. [J. Am. Chem. Soc. 117 (1995) 12528].
Scaling of Time Variable and Constant Heating Rate Measurement
Authors: Yoshikazu Tanabe Yoshikazu Tanabe
Published: October 2002

In isothermal changes of physical quantities, the time variable t is frequently scaled by a characteristic time, τ. The scaling property of the time variable causes τq to become approximately constant for changes in the heating rate, q, of many orders of magnitude. This means that the activation energy can be derived from constant heating rate measurements. The case of a stretched exponential function is discussed in detail, and an example calculation is carried out for the cis-trans thermal isomerization of polyacetylene films.
Simple System for Dual-Parameter Multichannel Pulse-Height Analysis
Authors: Kusakabe Toshio , Norizawa Hiroshi Taniguchi
Published: October 2002

A dual-parameter multichannel pulse height analyzer has been simply constructed by use of two analog-to-digital converters, a digital input/output board and a personal computer. The control program for data acquisition and graphic display was written in an assembler. Stored data were promptly displayed on a monitor in both a contour and an isometric display. This system is simple to operate and applicable to any field of radiation measurement.
Estimation of Position and Relative Permittivity of Dielectric in a Cylindrical Air Condenser by New Capacitance Measurement Method
Authors: Akira Kimoto Akira Kimoto , Katsunori Shida Katsunori Shida
Published: October 2002

In this work, a new capacitance measurement method for collecting the data used to estimate relative permittivity distributions is proposed. The proposed method involves measuring the capacitance between a pair of measurement electrodes using various combinations of supplementary electrodes. This method can be used to obtain many types of information in each measurement, which cannot be acquired using conventional capacitance measurement methods. We first estimate the position and relative permittivity of a small dielectric column in a homogeneous cylindrical air space, and then discuss the effectiveness of our new capacitance measurement method. The great potential of this method is thus demonstrated.
Chaotic Dynamics and Rheology of Suspensions of Periodically Forced Slender Rods in Simple Shear Flow
Authors: Kumar K. Satheesh , S. Savithri S. Savithri , T. R. Ramamohan T. R. Ramamohan
Published: October 2002

In an earlier paper, we had outlined a procedure for calculating the rheological parameters for periodically forced suspensions of slender rods in simple shear flow in the chaotic regime. In this work, we examine the consequences of the above procedure on the dynamics and rheology of similar suspensions starting off with uniform initial orientation distributions as well as aligned initial distributions. We provide numerical evidence for existence of riddled and intermingled basins of attractions in the system. We discuss the limitations of the diffusion equation approach in the chaotic regime. We also demonstrate that small changes in the preparation of aligned suspensions can lead to dramatically different rheological behaviour in some parametric regimes. In other parametric regimes differences in the dynamical behaviour do not translate into differences in the rheological behaviour of aligned suspensions.
Localized Fluctuation of a Two-Dimensional Atomic-Scale Friction
Authors: Fujisawa Satoru , Sugawara Yasuhiro , Morita Seizo
Published: October 2002

By carrying out a fast line scan 10° tilted from perpendicular to a row of the stick-points on a cleaved graphite surface, we observed localized fluctuation of a two-dimensional atomic-scale friction using a two-dimensional frictional force microscope. The analysis which was based on a two-dimensional stick-slip model revealed that the localized fluctuation on an atomic scale exhibits three kinds of tip trajectory and that one trajectory exhibits a slip motion with an almost 90° angle from the fast line scan direction. This localized fluctuation enabled us to observe square-wave signal with a subangstrom lateral width which indicates the achievement of subangstrom lateral resolution with a microscope for the first time. Furthermore, the origin of the three possible trajectories was explained well by an extended two-dimensional stick-slip model with the effective adhesive area. Therefore, this extended model is useful for studying the origin of the fluctuation of an atomic-scale friction.
Photoinduced Formation of Semiconductor Nanocrystals in CdS-Doped Glasses
Authors: Tadaki Miyoshi Tadaki Miyoshi , Yoshitaka Araki Yoshitaka Araki , Ken-ichi Towata Ken-ichi Towata , Hirobumi Matsuki Hirobumi Matsuki , Naoto Matsuo Naoto Matsuo
Published: October 2002

Luminescence and electron spin resonance (ESR) of CdS-doped glass which did not contain nanocrystals of CdS were investigated. Luminescence intensity increases after laser irradiation. Luminescence and ESR spectra after laser irradiation are similar to those of CdS-doped glass which contains nanocrystals of CdS. These results indicate that the nanocrystals are formed after laser irradiation.
Surface Particle Analysis of SIMOX (Separation by IMplanted OXygen) Wafers
Authors: Kajiyama Kenji , Ohtsuka Susumu , Yoji Morikawa Yoji Morikawa , Takayuki Yano Takayuki Yano
Published: October 2002

Particles were analyzed on the surface of low-dose SIMOX (Separation by IMplanted OXygen) wafers of SOI (silicon on insulator) structures. Particles were detected by the laser-scattering method, using s-polarization at an oblique incident angle and side detection angle. In spite of interference scattering caused by SOI interface micro-roughness, 0.2 µ m particles were successfully detected. Particle shape and composition were analyzed by scanning electron microscope, electron-probe micro-analysis and atomic force microscope. Consequently, particles were presumed to derive from ion-beam sputtered materials. In addition, smaller particle detection problems were examined by means of the light-scattering theory.
Characterization of Crystallinity in Low-Temperature-Grown GaAs Layers by Raman Scattering and Time-Resolved Photoreflectance Measurements
Authors: Abe Hajime , Harima Hiroshi , Nakashima Shin-ichi , Tani Masahiko , Sakai Kiyomi , Tokuda Yasunori , Kanamoto Kyozo , Abe Yuji
Published: October 2002

Low-temperature-grown GaAs homo-epitaxial layers were studied by Raman scattering and time-resolved photoreflectance techniques. Raman spectral profiles, polarization properties and lifetimes of photo-induced carriers depend strongly on growth conditions and post annealing. The experimental results showed that heavily defective layers were formed in as-grown layers, while post-annealed layers were less defective and consisted of partially misoriented crystallites or polycrystals. The carrier lifetime was short and the magnitude of the optical response was small in defective layers grown at relatively low temperatures, while the optical response was increased by annealing and by increasing the growth temperature. Of the samples tested, GaAs layers grown at 200–250° C and post-annealed layers gave a lifetime of 0.3 ps with relatively high optical response.
Defects in Ion-Implanted 3C–SiC Probed by a Monoenergetic Positron Beam
Authors: Uedono Akira , Itoh Hisayoshi , Ohshima Takeshi , Aoki Yasushi , Yoshikawa Masahito , Nashiyama Isamu , Okumura Hajime , Yoshida Sadafumi , Moriya Tsuyoshi , Kawano Takao , Shoichiro Tanigawa Shoichiro Tanigawa
Published: October 2002

Defects introduced by 200-keV N2
+- or Al+-implantation into 3C–SiC were probed by a monoenergetic positron beam. Depth profiles of the defects were determined from measurements of Doppler broadening profiles of the annihilation radiation as a function of incident positron energy. For ion implanted specimens at high substrate temperature (≥800° C), the major species of defects was identified to be vacancy clusters. The depth profile of vacancy-type defects was found to be shifted towards the surface of the specimen by implantation at high temperatures. Upon furnace annealing after the implantation, an agglomeration of vacancy-type defects was observed, and interstitial clusters were introduced below the vacancy-rich region.
Comparison of GaAs, InGaAs, and GaAs/InGaAs Doped Channel Field-Effect Transistors with AlGaAs Insulator Gate
Authors: Wen-Shiung Lour Wen-Shiung Lour
Published: October 2002

Heterojunction field-effect transistors (HFET's) with a GaAs, an InGaAs, and a GaAs/InGaAs doped channel have been fabricated and compared. The HFET's with an InGaAs doped channel show better performance than that of HFET's with a GaAs doped channel. Another device with a high-low double GaAs/InGaAs doped channel exhibits a much higher breakdown voltage. The parallel conduction and transconductance suppression could be avoided in the doped-channel FET's. All devices display broad plateaus on their transconductance vs. gate-to-source voltage profiles through a large voltage swing. For 1.5×100 µ m2 devices, the measured extrinsic transconductances (breakdown voltages) are 130 (15), 152 (17), and 184 (25) mS/mm (V) for a GaAs, an InGaAs, and a GaAs/InGaAs double strained doped channel FET's, respectively.
Electrical Characterization of Au/p-ZnSe Structure
Authors: Ohtsuka Ken-ichi , Suita Muneyoshi , Endoh Yasuyuki , Imaizumi Masayuki , Toshiro Isu Toshiro Isu , Masahiro Nunoshita Masahiro Nunoshita
Published: October 2002

Au electrodes were deposited on p-ZnSe layers grown by molecular beam epitaxy (MBE) and gas source (GS) MBE. The influences of the chemical pretreatment before electrode formation and the following heat treatment on electrical characteristics were investigated. All of the samples showed nonohmic current flow. In MBE-grown samples before heat treatment, pretreatment lowers the voltage of current flow rise from 6 V to 4–5 V. On the other hand, GSMBE-grown samples with and without pretreatment showed current flow rise at 4–5 V. The increase of the voltage of current flow rise was observed after heat treatment, irrespective of pretreatment and the growth method. This is related to the difference in the as-grown surface between MBE and GSMBE. The resistivity of the p-ZnSe layer increased slightly after heat treatment below the growth temperature.
Abnormal Surge Responses in Bi-directional Thyristors at High Surge Current
Authors: Yoshio Shimoda Yoshio Shimoda , Hidetaka Satoh Hidetaka Satoh
Published: October 2002

Abnormal surge response in bi-directional thyristors at high surge currents is analyzed. This phenomenon presents an abrupt increase in the on-voltage with a peak. As the applied surge current increases, the peak value of the on-voltage becomes higher, and the peak occurrence time decreases. The on-voltage increase is caused by the temperature dependence of Auger recombination and carrier mobility. The decrease in mobility and lifetime governed by the Auger effect are enhanced due to self-heating caused by the surge current. The analysis agrees reasonably well with theoretical considerations.
Assessment of the Structural Properties of GaAs/Si Epilayers Using X-Ray (004) and (220) Reflections
Authors: Maosheng Hao Maosheng Hao , Yutian Wang Yutian Wang , Chunlin Shao Chunlin Shao , Tetsuo Soga Tetsuo Soga , Junwu Liang Junwu Liang , Takashi Jimbo Takashi Jimbo , Masayoshi Umeno Masayoshi Umeno
Published: October 2002

We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.
Advantages of RuOx Bottom Electrode in the Dielectric and Leakage Characteristics of (Ba,Sr)TiO 3 Capacitor
Authors: Lee Yong Tae Kim
Published: October 2002

The crystal structure and electrical properties of (Ba,Sr)TiO3 (BST) films were investigated with three different bottom electrodes, Ti/Pt, RuOx and RuOx/Pt. On the RuOx and RuOx/Pt electrodes BST films were preferentially grown along the same orientations of electrodes, whereas BST films have no preferential orientation on the Pt electrode. The interfacial reaction, oxygen deficiency and hillock formation in the BST capacitors were obviously prevented by the RuOx bottom electrode, resulting in a high dielectric constant (300–305) and low leakage current density (10-9 A/cm2).
Direct Observations of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Homopolyester by Scanning Tunneling Microscopy
Authors: Dae Ken Nakajima
Published: October 2002

The structure of a main-chain thermotropic liquid-crystalline homopolyester, poly [(phenylsulfonyl)- p-phenylene 1,10-decamethylene-bis(4-oxybenzoate)] (PSHQ10), having a melting point of approximately 110°C and the nematic-isotropic transition temperature of approximately 175°C, was investigated using scanning tunneling microscopy (STM). For taking STM images we employed two samples of PSHQ10: sample A was an as-cast film which received no thermal treatment and sample B was an as-cast film which was thermally treated above the melting point. The STM images show that (i) sample A has a molecular arrangement which is in good agreement with the crystallographic data obtained in a wide-angle X-ray diffraction study, and (ii) sample B has both crystal-like and bundle regions. The STM images of sample B are interpreted as representing a structure which, according to results obtained by Han et al. [Macromolecules 26 (1993) 3176], is a high-temperature melting crystal formed via recrystallization during annealing.
High-Power Single-Mode Flared Laser Diode with an Intermediate-Width Stripe at the Flare Base
Authors: Shin'ichi Nakatsuka Shin'ichi Nakatsuka , Kenji Uchida Kenji Uchida
Published: October 2002

A high-power laser diode with a flared stripe is investigated. Beam shape analysis is carried out to optimize the stripe shape. Calculations show that the spot size at the laser facet strongly depends on the length of the intermediate stripe and, compared to a conventional stripe laser diode, a 33% increase in the stripe area of this structure can increase more than triple the catastrophic optical damage (COD) power. Laser diodes fabricated according to the calculation show characteristics consistent with the calculation results and a 380 mW output-power laser diode with an 80 mA threshold current is obtained by using this structure. This laser diode attained single-mode operation up to a maximum of 200 mW and could be operated for more than 1000 h at 50° C at an output of 100 mW.
Compositional Modulation of Two-Dimensional Layered Perovskite (RNH3)2Pb(Cl, Br, I)4 and Its Optical Properties
Authors: Nobuaki Kitazawa Nobuaki Kitazawa
Published: October 2002

The compositional modulation of two-dimensional layered perovskites, (RNH3)2Pb(X, I)4(R: C6H5C2H4-; X: Cl, Br), and optical properties of these materials were investigated. Thin films of microcrystalline (RNH3)2- Pb(X, I)4 were successfully fabricated by the spin-coating method. X-ray diffraction spectra revealed that these materials could be regarded as inorganic/organic superlattice structures. In the spectra obtained for the (RNH3)2Pb(Br, I)4 films, a strong exciton absorption band was observed even at room temperature, and the peak position shifted continuously towards the blue and violet regions. The exciton absorption bands observed in the spectrum of (RNH3)2Pb(X, I)4 mixed crystal were consistent with the 6s to 6p transition of Pb2+. The peak shift of the exciton absorption bands of these materials could be explained by the valence band structure composed of the Pb(6s) orbital which was hybridized with the I(5p) and X(np) orbitals.
Design of Frequency-Domain Filters for Femtosecond Pulse Shaping
Authors: Kazuya Takasago Kazuya Takasago , Tetsuya Itoh Tetsuya Itoh , Makoto Takekawa Makoto Takekawa , Ken-ichi Utoh Ken-ichi Utoh , Fumihiko Kannari Fumihiko Kannari
Published: October 2002

As a calibration method for frequency-domain filters in Fourier-transform synthesis of arbitrarily shaped laser pulses, the spatial amplitude and phase profile of the filter were reconstructed from the synthesized temporal pulse shape and its spectrum using a simple iterative method. We also developed a design procedure for phase-only filters to synthesize both temporal phase and amplitude even for asymmetric pulse profiles of femtosecond laser pulses.
Effects of Electrode Geometry and Gas Pressure on Breakdown Voltage of a Pseudospark Discharge
Authors: Higuchi Kazuya , Shimada Tsutomu , Itagaki Minoru , Abe Teruyuki Sato
Published: October 2002

The breakdown voltage of a pseudospark discharge device is measured for a wide range of nitrogen gas pressure, p, and various geometrical dimensions of the electrodes, i.e., anode-cathode gap distance, L, diameter of hole, d, thickness of the electrode, t, and depth of hollow cathode cavity, h. The empirical scaling relation obtained is expressed as V
s=3.06×102
p
-3.37
L
-1.16
d
-2.25. This relation shows that the breakdown voltage is a function of p
3.37, as opposed to the p
2
L or p
L dependence. The geometrical effect of the electrodes on the breakdown voltage characteristic can be explained by introducing the effective discharge length, which is defined as the width of the spatial profile of the calculated electric field.
Construction of a Compact Spin- and Angle-Resolved Photoelectron Spectrometer
Authors: Takahashi Naoshi , Tanaka Shin-ichiro , Ichikawa Masatake , Ohara Shigeo , Fujii Yasuo , Nakanishi Koichi , Masao Kamada Masao Kamada
Published: October 2002

A compact photoelectron spectrometer has been constructed to analyze energy, momentum and spin of the electronic states in condensed matter. The spectrometer consists of an electron energy analyzer, lens systems and a spin detector. The spin detector is a low-energy diffuse scattering type instrument with a potential of about 100–250 eV. The detector consists of a 90° deflector, a gold target, a four-section anode and lens systems. The detector is about 0.15×0.05×0.05 m3 in size and is rotatable along a single axis in the analysis chamber under ultra-high vacuum conditions. The parameters of the optical elements have been determined through optimization of the photoelectrons from GaAs(100) and with reference to the ray tracing calculation. The performance of the spin detector has been verified by observing the spin-polarized electrons from O/Cs/GaAs(100).
Design and Performance of a Rotary Motor Driven by Piezoelectric Stack Actuators
Authors: Khanh Duong Khanh Duong , Ephrahim Garcia Ephrahim Garcia
Published: October 2002

The development of a rotary inchworm-motor using piezoelectric actuators is presented. The motor design has the advantage of a macro and micro stepper motor with high torque and speed. The design is capable of fast angular positioning with micro level accuracy. The rotary motor, as designed, can also be used as a clutch/brake mechanism. A constructed prototype motor along with its characteristics are presented. The motor consists of a torsional section that provides angular displacement and torque, and two alternating clamping sections which provide the holding force. The motor relies on the principal piezoelectric coupling coefficient (d
33) without torsional piezoelectric elements. This design eliminates bending moment and shear applied to the actuator elements and thus increases its torque capability. An innovative flexure design is introduced and consideration is given to contact elements which affect the performance of the motor. Experimental results demonstrating the prototype's performance based on the aforementioned design considerations are presented.
Seventy-nm-Pitch Patterning on CaF 2 by e-beam Exposure
Authors: Hiroo Hongo Hiroo Hongo , Tetsuya Hattori Tetsuya Hattori , Yasuyuki Miyamoto Yasuyuki Miyamoto , Kazuhito Furuya Kazuhito Furuya , Takeshi Matsunuma Takeshi Matsunuma , Masahiro Watanabe Masahiro Watanabe , Masahiro Asada Masahiro Asada
Published: October 2002

We report fine pitch patterns of polycrystalline \caf film deposited on an InP substrate formed by e-beam exposure. Ten periods of 70-nm-pitch line patterns were fabricated. The linewidth fluctuation was found to depend on the grain size of the \caf film.
Flash Technology: Challenges and Opportunities
Authors: Raghupathy V. Giridhar Raghupathy V. Giridhar
Published: October 2002

Flash memory is a rapidly growing segment of the semiconductor memory market. It occupies a unique place among semiconductor memories by offering the combination of non-volatility, electrical re-writability and high density. Several alternate Flash cell structures have evolved that offer differing tradeoffs for cost and performance. The Flash memory market has been valued over $1.9 Billion (US) in 1995 and accounts for about 3.5% of the overall semiconductor memory market. Flash memory is the fastest growing segment of the non-volatile semiconductor memory market. This paper examines the challenges and opportunities in Flash technology using ETOX
T
M
cells as an example. Flash poses some unique challenges in controlling tunneling and in voltage scaling. Flash also presents a unique opportunity for scaling storage density through multi-level cells.
MASCOT: Mask Pattern Correction Tool Using Genetic Algorithm
Authors: Haruki Tamae , Asai Satoru , Kenji Nakagawa Kenji Nakagawa , Isamu Hanyu Isamu Hanyu
Published: October 2002

We propose a new optical proximity correction (OPC) method using a polygonal mask model and a genetic algorithm (GA). With the polygonal mask model, our method can generate simple and practical masks that satisfy the constraints arising from manufacturing requirements. A robust optimization method, the genetic algorithm was adopted for obtaining adequate modifying ability for a given arbitrary mask pattern. For some of these mask patterns, the characteristics of distortion due to the optical proximity effects (OPE) are not well-known. GAs simulate the free-competition among animals through generation alternation is recognized as the algorithm that can avoid being stuck in local optima in multi-modal optimization problems. We developed our mask pattern correction tool (MASCOT) using the mask model and the optimization method. Experimental results showed great improvement in the generated resist pattern. Satisfactorily practical computational performance was obtained in our experiments with a workstation.
Improvement of Interface Properties in µc-SiC/poly-Si/µc-Si Double Heterojunction Solar Cell
Authors: Ma Wen , Hiroaki Okamoto Hiroaki Okamoto , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

A new type of double heterojunction thin film solar cell has been developed with a p µ c-SiC/n poly-Si/n µ c-Si/Al structure. By efficiently employing the wide band gap window effect and the back surface field (BSF) effect with hydrogen passivation treatment, a fill factor higher than 80% has been obtained with a conversion efficiency of 17.2%. In order to determine the detailed mechanism of the enhancement of cell performance, a systematic measurement of the rear interface recombination velocity has been performed using poly-Si based solar cells with the p µ c-SiC/a-SiC/n poly-Si/n µ c-Si/Al structure. It is found that the interface recombination velocity decreases by more than one order of magnitude with the insertion of the n µ c-Si rear side layer. Possible mechanisms for the improvement of cell performance are discussed on the basis of a series of characterizations of the devices with several different interface layers.
Second Harmonic Generation from Si1-xGex Epitaxial Films with a Vicinal Face: Film Thickness Dependence
Authors: Mizutani Goro , Sonoda Yasuyuki , Ushioda Sukekatsu , Maeda Takahiro , Murota Junichi
Published: October 2002

We have observed optical second harmonic generation in Si1-
x

Ge
x
(x=0.685) crystalline films grown on Si(001) substrates. The substrates are oriented 4 degrees off the [001] direction rotated about the [100] axis. We have measured the SH intensity as a function of the film thickness and the sample rotation angle about the surface normal. The intensity pattern changes as the film thickness is varied from 110 nm to 58 nm. For the film thickness of 110 nm the intensity curve as a function of the rotation angle has three maxima. This angular pattern can be reproduced by a model that includes the effect of interference between the surface and bulk second harmonic amplitudes. For the film thickness of 58 nm the angular pattern has only one maximum. In this case the surface SHG dominates the observed intensity and no interference effect is observed.
Precise Stress Control of Ta Absorber using Low Stress Alumina Etching Mask for X-Ray Mask Fabrication
Authors: Iba Yoshihisa , Kumasaka Fumiaki , Aoyama Hajime , Takao Taguchi Takao Taguchi , Masaki Yamabe Masaki Yamabe
Published: October 2002

In the stress control of an X-ray mask absorber, the repeatability of control and stability are important. We found that the change in the stress in a Ta film resulting from annealing depends on the oxygen concentration in the film; the magnitude of the stress change is determined by the annealing temperature and time. Using this characteristic of Ta film, we have successfully controlled the stress in the Ta absorber to less than 5 MPa with good repeatability. In our mask fabrication process, Al2O3 film was used as an etching mask. We found that the Al2O3 film prevented the Ta absorber stress from changing in high-temperature atmospheres because the Al2O3 film prevented oxygen diffusion into the Ta film. Utilizing Al2O3 films, we succeeded in preventing changes in Ta absorber stress in the thermal processes after Ta stress control, such as frame bonding and resist baking. Consequently, we were able to precisely control the Ta absorber stress in X-ray masks with good repeatability and stability in a realistic X-ray mask fabrication process.
Simulation of X-Ray Mask Pattern Displacement
Authors: Oda Masatoshi , Shingo Uchiyama Shingo Uchiyama , Tadahito Matsuda Tadahito Matsuda
Published: October 2002

We have developed programs to calculate pattern displacement caused by membrane stress, absorber stress distribution and pattern density in X-ray masks. This paper describes the models upon which the calculations were based and shows how the results fit experimental ones. The membrane area shrinkage caused by SiN stress is calculated using a previously reported method. The pattern displacement caused by absorber stress is calculated using the stress gradients estimated for each point from the stress distribution measured in masks used in practice. It is found that the displacement in the membrane with non-patterned absorber is strongly affected by the absorber stress distribution. The influence of pattern density on pattern displacement is calculated using a model in which the absorber thickness is reduced in accordance with the volume etched off during patterning. Comparisons between calculated and experimental results of the pattern displacement in masks with simple patterns reveal that the calculated results agree with the experimental results with an accuracy of about 30 nm.
Influence of Crystallinity on the Electrical Property of KFe(S1-xSex)2
Authors: Nishioka Shido , Hisao Kuriyaki Hisao Kuriyaki , Kazuyoshi Hirakawa Kazuyoshi Hirakawa
Published: October 2002

The electrical properties of KFe(S1-
x

Se

x

)2 (0≤x≤0.89) were studied on crystals annealed for a long period. The resistivity ρ along the c-axis shows high values: 1.6×104 Ω·cm for x=0 and 8.6×101 Ω·cm for x=0.89 at 290 K. The nonmetallic temperature-dependent resistivity is approximated by ρ∝exp
[(T
0/T)1/2], where T
0 is a constant. Both the susceptibility and the Seebeck coefficient show metallic behavior. Observations using a transmission electron microscope indicate that the specimens consist of many grains. It is concluded that these compounds are essentially metallic. The high resistivity and the nonmetallic temperature dependence are ascribed to the imperfections in the crystal.