bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo-Current Multiplication Phenomenon of Amorphous Silicon-Based Multilayer Photodiodes Fabricated on Crystalline Silicon Substrate
Authors: Kitamura Ken , Ishida Kouichi , Morimoto Takashi , Masuda Satoshi , Okumura Yoshihiro , Miyatake Shigehiro , Hatanaka Yoshinori
Published: October 2002

Recently, high-resolution and high-density solid-state imaging devices have been in high demand due to their high photogain because the smaller pixel size makes the smaller photo-current dependent on the reduced area. Multilayer photodiodes having a-SiC:H/a-Si:H/a-SiN:H structures fabricated on the crystalline silicon (c-Si) substrate were studied for their photo-multiplication effects which marked a gain of 6.6. These multiplication phenomenona arose in the wavelength region longer than 550 nm, while in the shorter-wavelength region, the photogain was less than unity. This is explained by the electron carrier process where the carriers photogenerated in the c-Si substrate are accumulated at the a-SiN:H/c-Si interface and tunneled via localized states in the a-SiN:H layer by the induced high electric field. From these results, it is considerably difficult to support the theory of avalanche effect to explain these photo-multiplication effects.
Electronic and Optical Characteristics of Multilayer Nanocrystalline Silicon/Adsorbed Oxygen Superlattice
Authors: Seo Yong-Jin , Tsu Raphael
Published: October 2002

The electronic transport and photoluminescence (PL) characteristics of the multilayer nanocrystalline silicon/adsorbed oxygen (nc-Si/O) superlattice formed by molecular beam epitaxy (MBE) were studied. The current–voltage (I–V) characteristics for hydrogen- and oxygen-annealed samples were quite symmetrical, and the device was stable up to a bias range from +30 V to -30 V. Also, the dI/dV characteristics showed jumps and negative conductance, which are due to electrically active defects and traps. To confirm the presence of the nanocrystalline Si structure, Raman scattering measurement was performed. The blue shift was observed in the PL peak of the oxygen-annealed sample, compared to the hydrogen-annealed sample, which is due to a contribution of smaller crystallites. Our results determine the right direction for the fabrication of silicon-based optoelectronic and quantum devices as well as for the replacement of silicon-on-insulator (SOI) in high-speed and low-power silicon MOSFET devices in the future.
Pulsed-Laser-Induced Microcrystallization and Amorphization of Silicon Thin Films
Authors: Higashi Seiichiro , Sameshima Toshiyuki
Published: October 2002

Pulsed-laser-induced microcrystallization and amorphization of Si thin films were investigated by transient reflectance and conductance measurements. It was clarified experimentally that the complete melting of a Si film and subsequent supercooling induces both microcrystallization and amorphization. In the case of the microcrystallization of a 49.1-nm-thick Si film, nucleation among supercooled liquid Si was observed. The nucleation temperature and resulting nucleation rate under the microcrystallization condition were estimated to be 1047 K and 1.67×1025 events/(cm3·s), respectively. On the other hand, no significant nucleation was observed in the case of a laser amorphization of 20.7-nm-thick Si film although the film was melted for the relatively long duration of about 80 ns. Extremely fast quench of liquid Si films seems to suppress nucleation and results in solidification in amorphous phase.
Device Applied Fowler-Nordheim Relationship
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji , Okuyama Fumio
Published: October 2002

A method for applying the Fowler-Nordheim (FN) relationship to analyze data pertaining to field emission (FE) devices is outlined. The emission current is obtained through integration of the FN current density over the emitter area, taking into account the local value of the electric field. The slope and intercept of the FN plots are used to plot the slope versus the intercept diagram, with emitter work function Φ and radius R as parameters. Each experimental current–voltage data set is represented in this diagram as a point inside the lattice of equi-Φ and equi-R lines, facilitating derivation of the actual Φ and R values. An analytical FE diode model and a numerical FE microtriode model are used to exemplify this approach. The method can be used as a convenient graphical tool to analyze the experimental results of FE.
An Analytical Method of Analyzing Insulated-Gate Bipolar Transistor Characteristics in Terms of Applied Terminal Voltages
Authors: Huang Tsung-Yi , Gong Jeng , Lai Jinn-Horng
Published: October 2002

An analytical method of analyzing insulated-gate bipolar transistor (IGBT) current–voltage characteristics is established in this paper. Important internal device parameters such as the injected carrier concentrations, electron and hole current densities and depletion length of the drift region are calculated as functions of the terminal voltages. The parasitic transistor current gains αnpn and αpnp are also extracted as functions of applied voltages. The temperature effect on both latch-up criteria can also be predicted from this method.
Crystalline Defects in InP-to-Silicon Direct Wafer Bonding
Authors: Pasquariello Donato , Camacho Martin , Ericsson Fredric , Hjort Klas
Published: October 2002

InP-to-Si wafer bonding has been proposed as a way of circumventing the problems associated with lattice-mismatch in heteroepitaxial growth. Therefore, in this study the dislocation density and material degradation in InP-to-Si hydrophobic bonding are evaluated. Both interface and InP bulk defects were studied using IR-transmission, atomic force microscopy (AFM) and defect-etching. When the bonded wafers were annealed below 300°C, no volume dislocations were generated in InP. However, when annealing above 300°C, the thermal mismatch stress induced large numbers of volume dislocations in InP. It was also shown that hydrophobic InP-to-Si wafer bonding unfortunately requires high-temperature annealing to achieve sufficient bonding-strength. However, a considerably lower dislocation density was observed in InP-to-Si wafer bonding than that in InP heteroepitaxial growth on Si. Also, when the samples were annealed above 400°C, asymmetric voids emerged at the interface. These voids are associated with the nucleation of indium droplets which causes microcavities at the interface where volume dislocations can sweep-out, forming surface steps. The voids completely disappeared when channel-patterned interfaces were used.
Single Crystal Growth and Improvement of the Superconductivity in Nd1-xPrxBa2Cu3Oy System
Authors: Fujita Yukitoshi , Suzuki Tadashi , Iwasaki Hideo
Published: October 2002

Superconducting characteristics have been studied from the viewpoint of the annealing condition on single crystals of the Nd1-x
PrxBa2Cu3Oy system grown by the travelling solvent floating zone (TSFZ) method. An anneal as the first step in Ar at 850–900°C gives the best superconducting characteristics in contrast to the anneal in O2. It is suggested that the annealing at high temperature in Ar causes the redistribution between the Pr(Nd)/Ba sites and strongly suppresses the occupancy to the Ba site by the Pr(Nd) ions.
Room-Temperature Magnetic and Magneto-Optical Properties of Sr2FeMoO6 Thin Films
Authors: Asano Hidefumi , Osugi Masahiro , Kohara Yasuhiro , Higashida Daisuke , Matsui Masaaki
Published: October 2002

Epitaxial thin films of a half-metallic ferromagnet Sr2FeMoO6 have been grown on (001) SrTiO3, and MgO substrates by magnetron sputtering in Ar+H2 mixture gas. Their structural, magnetic, magneto-optical and transport properties at room temperature were investigated and compared. Large difference has been observed especially in the magnetic and magneto-optical properties between thin films on SrTiO3 and MgO. The films on SrTiO3 exhibited stronger out-of-plane magnetic anisotropy and larger complex polar Kerr effect with a rotation θk up to -0.32° at 1.6 eV and RT. The observed difference in the properties of the films on the two substrates can be interpreted in terms of the structural disorder.
Direct Observation of Domain Structure and Magnetization Reversal of Magnetic Thin Films Using Lorentz Transmission Electron Microscopy
Authors: Yu Andrew Chak Chung , Petford-Long Amanda , Miyazaki Terunobu
Published: October 2002

Lorentz transmission electron microscopy (LTEM) was used to characterize the domain structure and the magnetization reversal process of Ni80Fe20 and Co films fabricated using magnetron sputtering. In-situ magnetizing experiments were performed in Fresnel imaging mode, while a long camera length mode (“reverse mode”) was employed for Foucault imaging. At low fields, magnetization ripple in the Co films showed higher magnetic contrast and angular distribution than in the NiFe films, which was due to the high anisotropy of Co. The NiFe films reversed via rapid wall motion while the Co films reversed mainly via slow moment rotation followed by wall motion. It is confirmed that domain wall mobility in the NiFe films is higher than that in the Co films. Profound columnar texture of the Co films observed in conventional transmission electron microscopy may enhance wall pinning and thus hinder wall mobility.
Mössbauer Studies on Exchange Interactions in CoFe2O4
Authors: Kim Sam Jin , Lee Seung Wha , Kim Chul Sung
Published: October 2002

Two polycrystalline samples of CoFe2O4 were prepared by slow cooling and quenching and studied using Mössbauer spectroscopy and X-ray diffraction. The crystals were found to have a cubic spinel structure with the lattice constants of the slowly cooled sample being a
0=8.381 Å and the quenched sample being a
0=8.391 Å. The temperature dependence of the magnetic hyperfine field in 57Fe nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the Néel theory of ferrimagnetism. For the slowly cooled sample, the intersublattice A–B superexchange interaction and intrasublattice A–A superexchange interaction were antiferromagnetic with a strength of J

A–B
=-25.0k
B and J

A–A
=-18.9k
B, respectively, while the intrasublattice B–B superexchange interaction was ferromagnetic with a strength of J

B–B
=3.9k
B. In the quenched sample, however, their strengths were J

A–B
=-22.6k
B, J

A–A
=-17.6k
B, and J

B–B
=3.9k
B, respectively.
Pulse Sequence Addressing for Gray-Scale Bistable Cholesteric Displays
Authors: Yip W. C. , Kwok H. S.
Published: October 2002

In the study of the transition dynamics, we found that the reflectance of bistable cholesteric displays depended on the addressing sequence of the bipolar pulses. Two different pulse amplitudes corresponding to the high and low voltages about the quiescent point were chosen. By a proper permutation of such pulses, the final reflectance of even difference could be obtained for gray-scale display applications. In contrast with the root-mean-square (rms) modulation techniques, this scheme proposed for the first time does not primarily depend on the rms voltage. In this paper, we study the electro-optics and the domain characteristics, and propose a phenomenological proposition to describe this effect. We shall also extend our previous driving scheme to demonstrate the gray-scale control at 5 ms/line addressing.
Light Figures and Group-to-Phase Velocity Ratio in Anisotropic Media
Authors: Mamedov Nazim , Yamamoto Nobuyuki , Kunie Akimori
Published: October 2002

It is shown that light figures can be employed for determination of the group-to-phase velocity ratio without measurements of the absolute value of refractive index. It is applicable to uniaxial media and, after generalization, to biaxial media. In some cases the sample thickness is not required. The method was applied to weakly biaxial TlInS2 semiconductor-ferroelectric with well-defined light figure patterns at room temperature. It is shown that the obtained results are consistent with the available data on optical transitions near the band gap of this material. In combination with measurements of interference fringe separation in polarized transmission intensity (PTI) spectra the proposed method is supposed to allow for the determination of the absolute values of refractive indices.
Microwave Dielectric Properties and Mixture Behavior of CaWO4–Mg2SiO4 Ceramics
Authors: Park Il-Hwan , Kim Beom-Soo , Kim Kyung-Yong , Kim Byong-Ho
Published: October 2002

In order to use at a high microwave frequency range, the microwave dielectric properties and the microstructures of the (1-x)CaWO4–xMg2SiO4 ceramics with dielectric constants below 10 were investigated. The (1-x)CaWO4–xMg2SiO4 ceramics have tetragonal structure, and quantitative and morphology analyses were performed using a scanning electron microscope (SEM), wave dispersive X-ray spectrometer (WDX) and backscattered electron image micrographs. The highest quality microwave dielectric properties of the (1-x)CaWO4–xMg2SiO4 ceramics as a function of the composition x agree well with the highest density and the highest extent of shrinkage at the most optimum sintering temperature. At the composition of x=0.1, the (1-x)CaWO4–xMg2SiO4 ceramics have excellent microwave dielectric properties: ε
r=10.0, Q·f=129858 GHz and τf=-49.6 ppm/°C.
Analysis of Switching in Perovskite Ferroelectrics on the Tetragonal Side of the Morphotropic Phase Boundary Using a Landau-Theory-Based Lattice Model with Polarization Vector Rotations
Authors: Ricinschi Dan , Ishibashi Yoshihiro , Iwata Makoto , Okuyama Masanori
Published: October 2002

The polarization reversal in perovskite ferroelectrics having a tetragonal phase is studied using the Landau-theory-based lattice model, extended to the three-dimensional polarization case. Switching at various electric field levels is analyzed for near and far distances from the theoretical morphotropic phase boundary (MPB), in the presence of the latent nuclei. The calculated time dependence of average polarization during switching is correlated with the changes of polarization profiles in the lattice. For low electric fields, switching can be achieved by polarization vector rotations triggered by infinitesimal tilting at the latent nuclei sites. Polarization vector rotations are most significant close to the MPB, where the free energy is isotropic in the space spanned by the polarization components. For electric fields beyond the longitudinal polarization instability, the transversal polarization components do not play a very significant role. Inferior retention properties near the MPB due to the polarization vector rotations are predicted, though higher reversal speed and lower switching threshold are expected.
Characterization of Cu2ZnSnS4 Thin Films Prepared by Vapor Phase Sulfurization
Authors: Katagiri Hironori , Ishigaki Naoya , Ishida Takeshi , Saito Kotoe
Published: October 2002

Cu2ZnSnS4 (CZTS) thin films could be successfully formed by vapor phase sulfurization of electron-beam-evaporated precursors on a soda-lime glass substrate. This film is an interesting material for absorber layer in a solar cell because all the constituents are readily available in the earth's crust. In this study, using a new type of precursors containing ZnS, we could achieve the strong adhesion of CZTS films to a glass substrate. From the result of scanning electron microscope (SEM) observation, it was confirmed that the surface morphology of CZTS films is much improved by using this new type of precursor. The X-ray diffraction pattern revealed that CZTS thin films have kesterite structures. From the measurement of transmittance and reflectance, the optical band-gap energy was estimated as 1.40–1.45 eV, which is very close to the optimum value for a solar-cell absorber. The highest open-circuit voltage of our cells based on CZTS films is 735 mV, which is a higher value than that reported in numerous other studies on CZTS.
Mössbauer Study on Crystallization Behavior of Glassy Fe58Co7Ni7ZrxB28-x (3 ≤x ≤18) Alloys with Variable Supercooled-Liquid Regions
Authors: Hideya Onodera Hideya Onodera , Takaomi Itoi Takaomi Itoi , Akihisa Inoue Akihisa Inoue
Published: October 2002

Crystallization behavior of glassy Fe58Co7Ni7ZrxB28-x
(3 ≤x ≤18) alloys was examined by means of X-ray diffraction and 57Fe Mössbauer spectroscopy in order to clarify the reason for the thermal stability against crystallization, where the thermal stability correlates strongly to the width of the supercooled-liquid region. Various crystalline phases appear in the specimens quenched from and annealed at temperatures 50 K higher than the crystallization temperatures. Crystalline Fe3B and Fe2B phases characteristic of the B-rich alloys appear along with Fe2Zr and unidentified Fe–Zr–B phases characteristic of the Zr-rich alloys in the quenched Fe58Co7Ni7Zr8B20 specimen that originally has the widest supercooled-liquid region of 66 K. The competitive frustration in the forming ability of these compositional short-range order is one of the reasons for thermal stability against crystallization. Both the quenched and annealed Fe58Co7Ni7Zr3B25 specimens do not contain any phase with the Zr constituent, while the glassy Fe58Co7Ni7Zr3B25 alloy has the supercooled-liquid region of 34 K. This fact implies that the Zr impurities in Fe3B- and/or Fe2B-type compositional short-range order also play an important role in the thermal stability of these glassy alloys.
Elastic Stiffness Properties of Brass near the Order–Disorder Transition: An Overview
Authors: Pal Barnana
Published: October 2002

An overview on the variation of the elastic stiffness constants of brass as a function of temperature, near the structural transition at T
c=468°C from an ordered β′-phase to disordered β-phase is presented in this report. Also, the variation of elastic stiffness constants c
11 and c
′
11 (=c
11 + c
12 + 2c
44) of brass, measured using the `coherent pulse/cw' technique has been reported. A simple modification of the technique has been made for the detection of the resonance frequencies in a sample of relatively small size.
Spectroscopic and Structural Studies of Cyanine Dyes in Functionalized Langmuir–Blodgett Films: Electron and Energy Transfer Processes
Authors: Ray Krishanu , Nakahara Hiroo
Published: October 2002

Formation of the J-aggregates with redshifted bands and the H-aggregates with blue-shifted bands for a long-chain merocyanine (MC) could be controlled by mixing the molecular matrix components in the monolayer assembly. The binary Langmuir–Blodgett (LB) film containing MC and Cd arachidate (AA) provided the J-aggregates which have a sharp fluorescence with less Stokes shift. The ternary LB system having MC–AA and octadecane (OD) showed the H-aggregates in addition to the J-aggregates. The structures of the J- and H-aggregates were studied by atomic force microscopy and X-ray diffraction analysis. Additionally, the photo-induced electron transfer from the MC J-aggregate donor to a long-chain bipyridilium and the energy transfer from another cyanine dye donor to the MC H-aggregate acceptor were investigated in the hetero-LB films by varying the separation between the donor and acceptor layers.
Formation of Three-Dimensional Silicon Mounds on the Si(111) 7 ×7 Surface Using the Tip of a Scanning Tunneling Microscope
Authors: Kazuhiko Hayashi Kazuhiko Hayashi , Ayahiko Ichimiya Ayahiko Ichimiya
Published: October 2002

Truncated triangular silicon pyramids are fabricated one by one on the Si(111) 7 ×7 surface in the temperature range from 400°C to 500°C. Two types of three-dimensional (3D) silicon mounds are fabricated with a mirror symmetry against the [101] direction. One type consists of normal stacking mounds with {311} and {221} on the side facets and a (111) on the top surface. The other type consists of silicon mounds with a stacking fault at the interface between the silicon mounds and the substrate surface, which have {311} facets, {331} facets and a (111) facet. Normal stacking mounds are produced with a probability of 75%. Silicon mounds with a stacking fault are produced with a probability of 25%. The difference in the formation energy between normal stacking mounds and silicon mounds with a stacking fault is about 0.07 eV per 1 ×1 unit cell at 500°C. Silicon mounds are fabricated with large tunneling currents and sample bias voltages near 0 V. During the production of silicon mounds, the scanning tunneling microscope (STM) tip moves away from the substrate surface by about 26 nm. The production rates of silicon mounds are 120 ±10 s-1 at 440°C, 220 ±20 s-1 at 465°C and 570 ±80 s-1 at 485°C. The activation energy required for the production of silicon mounds is 1.3 ±0.1 eV and the pre-exponential factor is 4 ×1011±1 s-1.
Field Emission Properties of a Potassium-Doped Multiwalled Carbon Nanotube Tip
Authors: Hu Binhui , Li Peng , Cao Jien , Dai Hongjie , Fan Shoushan
Published: October 2002

The field emission properties of a single closed multiwalled carbon nanotube tip were investigated before and after doping with potassium. The threshold voltage was significantly reduced from 143 V to 76 V, but the emitter degraded in about 4 min. The current-voltage measurements fit the Fowler-Nordheim equation well up to about 100 nA of emission current. Additionally the work function of the multiwalled carbon nanotube tip could be estimated as being about 5.3 eV.
Correlation between Metastable and Ground-State Fluorine Atom Densities Measured by Laser-Induced Fluorescence and Vacuum Ultraviolet Absorption Spectroscopies
Authors: Kazuki Takizawa Kazuki Takizawa , Koichi Sasaki Koichi Sasaki , Kiyoshi Kadota Kiyoshi Kadota
Published: October 2002

The correlation between F atom densities at the ground state and the metastable state was determined in high-density fluorocarbon plasmas by laser-induced fluorescence (LIF) and vacuum ultraviolet absorption spectroscopies. A proportional relationship has been determined between the metastable and ground-state F atom densities, which can be understood reasonably well by considering the production and loss processes of the metastable state. The metastable state is produced from the ground state by electron impact excitation. According to the results of lifetime measurements, the loss of the metastable state is dominated by electron collision in high-density plasmas (≥2×1012 cm-3). Since both the production and the loss of the metastable state are dominated by electron impact processes, the density of the metastable state is proportional to the ground-state F atom density. The present experimental results suggest the possibility of monitoring the spatial distribution of the ground-state F atom density using LIF detection of the metastable state.
Motional Resonances of Sympathetically Cooled 44Ca+, Zn+, or Ga+ Ions in a Linear Paul Trap
Authors: Kai Yoshiki , Toyoda Kenji , Watanabe Masayoshi , Urabe Shinji
Published: October 2002

44Ca+, Zn+, or Ga+ ions are sympathetically cooled by Coulomb interaction with laser-cooled 40Ca+ ions, and motional resonances of these ions are observed by monitoring the fluorescence of the 40Ca+ ions. In the experiment of sympathetic cooling of 44Ca+, the ratio of the decrease in the fluorescence signal at the motional resonance of the sympathetically cooled species to that at the motional resonance of the laser-cooled species is almost proportional to the number ratio of the two species. In the case of Ga+ ions as the sympathetically cooled species, the change in the response of sympathetically cooled species becomes larger as the temperature of the ion cloud decreases. Crystallization of an ion cloud which contains both 40Ca+ and Zn+ (or Ga+) is observed.
Methanol Gas Sensing Using Ultramicroelectrodes: Studies on Sensing Mechanism and Its Enhancement
Authors: Umeda Minoru , Kabasawa Akihiro , Kokubo Mitsuhiro , Mohamedi Mohamed , Itoh Takashi , Uchida Isamu
Published: October 2002

Electrochemical detection of methanol vapor has been achieved using a highly sensitive small detector by an ultramicroelectrode-based electrochemical method. First, a peak current was observed by employing potential sweep voltammetry at a microring ring electrode. The current peak was confirmed to be that of the methanol vapor. Next, (i) the potential-sweep rate dependence of the peak current at the microring ring electrode, and (ii) the electrode-gap width dependence of the cyclic voltammogram at the microgap electrode were measured. Based on the results, the electrochemical-detection mechanism of vapor methanol has been proposed. Finally, an enhancement method for detecting methanol vapor was achieved by the proposed mechanism. Namely, using a Nafion\circledR-membrane-coated dualmicroelectrode we succeeded in detecting the methanol vapor by approximately 200 times higher than that by the bare electrode at an applied voltage of 4 V.
Development of a New Design Technique for Surface Acoustic Wave Ladder Filters
Authors: Roh Yongrae , Lee Youngjin , Lee Seunghee
Published: October 2002

Design of surface acoustic wave (SAW) ladder filters has been performed by trial and error, that is, by modifying the design variables step by step until performance of the filter satisfies given specifications. In this work, a new design method is developed that automatically determines the detailed pattern of a SAW ladder filter to meet all the given specifications. As a first step for the development, an analysis tool for the SAW ladder filter is produced by means of the Smith equivalent circuit analysis technique, and its validity is verified through comparison of calculated results with experimental data. With the analysis tool, we investigate variation of the filter performance in relation to the change in its design factors, and the results lead to the design algorithm. Validity and efficiency of the algorithm are illustrated with an exemplary design of a SAW ladder filter for cellular phones. The design scheme developed in this paper is so general that it can be applied to any other types of SAW filters too.
Far-Infrared Excitations in an Antidot at Finite Magnetic Fields
Authors: Emperador Agustí , Pi Martí , Barranco Manuel , Lipparini Enrico , Serra Llorenç
Published: October 2002

We have investigated the far-infrared dipole modes of an antidot submitted to a perpendicularly applied magnetic field B. The ground state of the antidot is described in local spin-density functional theory, and the spectrum in time-dependent local spin-density functional theory. The results are compared with those corresponding to a quantum dot of similar electronic surface density. The method is able to reproduce two of the more salient experimental features, namely, that the main bulk and edge modes have the same circular polarization, and that the negative B dispersion edge branch oscillates, with minima at the B values corresponding to fully occupied Landau levels. It fails, however, to achieve the unique feature of short-period antidot lattices that the energy of the edge magnetoplasmon approaches the cyclotron frequency for small B values. The existence of anticyclotron-polarized bulk modes is discussed, and a detailed account of the dipole spin mode is presented.
Segmented Electron-Beam Diodes for Pumping Large-Aperture KrF-Laser Amplifiers
Authors: Okuda Isao , Owadano Yoshiro
Published: October 2002

The design of the segmented electron-beam (e-beam) diodes and e-beam generation in the 60-cm aperture KrF-laser amplifier in our laboratory are reported. Reduction of self-magnetic fields in the segmented-diode configuration to reduce e-beam pinching is discussed with the measured e-beam currents. Diode segmentation in a still larger-aperture amplifier for inertial-fusion-energy drivers is also discussed.
Oxidation Simulation of Heavily Phosphorus-Doped Silicon based on the Interfacial Silicon Emission Model
Authors: Uematsu Masashi , Kageshima Hiroyuki , Shiraishi Kenji
Published: October 2002

Silicon oxidation of heavily phosphorus-doped substrates is simulated based on the interfacial silicon emission model. We assume that double negatively charged vacancies (V2-) from the substrates reduce the interfacial silicon emission, which governs the oxidation rate at the interface. The simulation is done by reducing the rate of Si-atom emission according to the concentration of V2- estimated from the carrier concentration of the substrates. In addition, the equilibrium concentration of oxygen in the oxide is increased with increasing P concentration to fit the experimental oxide thickness.
Characterization of the Interface between the Top Si and Buried Oxide in Separation by Implanted Oxygen Wafers
Authors: Takahashi Mitsutoshi , Nakashima Sadao , Kodate Junichi , Ohno Terukazu
Published: October 2002

The electrical characteristics of the top Si-buried oxide interface in low-dose separation by implanted oxygen (SIMOX) wafers have been investigated from high-frequency and quasi-static capacitance–voltage (C–V) measurements of the buried metal oxide semiconductor (MOS) diodes proposed here. The structure of the interface has been also analyzed using cross-sectional transmission electron microscopy (XTEM). SIMOX wafers with an internal thermal oxidation (ITOX) process have a fixed charge density of 2.7×1010 cm-2 and an interface trap density of 5×109 cm-2 eV-1. XTEM analysis revealed the undulation of the interface with ITOX is about 1 lattice. From the small fixed charge density and the smooth interface, we conclude that the strain field in the top Si-buried oxide interface is small, and comparable to that of thermal oxide-Si interface. The obtained results indicate that ITOX-SIMOX wafers are useful for the fabrication of fully depleted MOSFETs.
Electroless Plating Ni Induced Crystallization of Amorphous Silicon Thin Films
Authors: Chen Ying-Chia , Wu Yew-Chung Sermon , Chao Chi-Wei , Hu Guo-Ren , Feng Ming-Shiann
Published: October 2002

There is a great demand to fabricate polycrystalline silicon films at low temperatures. A metal-induced crystallization method can significantly decrease the crystallization temperature of amorphous silicon (a-Si). Metal thin films are generally deposited on a-Si by the physical vapor deposition method followed by crystallization at a temperature lower than 600°C. In this study, a faster and more inexpensive electroless Ni plating method was introduced. It was found that Si crystallinity increased with Ni plating time, but dropped when the time reached 10 min. When the plating time was less than 5 min, all of the poly-Si became needlelike with preferred orientation parallel to the substrate.
Low Frequency Noise of InP/InGaAs Heterojunction Bipolar Transistors
Authors: Penarier A. , Pascal F. , G-Jarrix S. , Delseny C. , Riet M. , Blayac S.
Published: October 2002

In this paper, we have studied the 1/f low frequency noise of self-aligned and non self-aligned InP/InGaAs heterojunction bipolar transistors (HBTs). The total noise of transistor is modeled by two current noise sources. The evolution with geometry, technological process and bias, of the current spectral densities referred to the input and output of the devices, permit us to locate the noise sources. Noise is mainly generated in the intrinsic transistor, and an extra noise perimetric source has been identified for the self-aligned transistors at the emitter periphery.
Density-Matrix Modeling of Terahertz Photon-Assisted Tunneling and Optical Gain in Resonant Tunneling Structures
Authors: Asada Masahiro
Published: October 2002

Photon-assisted tunneling current under terahertz (THz) irradiation is analyzed for resonant tunneling structures using the density-matrix theory. Close agreement with measured results was obtained. The analysis is extended to the THz optical gain due to the inter-quantum well transition which is the most important factor in the discussion on developing intersubband THz lasers.
A Small-Sized Lateral Trench Electrode Insulated Gate Bipolar Transistor for Improving Latch-up and Breakdown Characteristics
Authors: Goo Kang Ey , Hyun Moon Seung , Young Sung Man
Published: October 2002

A new small-sized lateral trench electrode insulated gate bipolar transistor (LTEIGBT) was proposed to improve the characteristics of the conventional lateral IGBT (LIGBT) and the lateral trench gate IGBT (LTIGBT). The entire electrode of the LTEIGBT was replaced with a trench-type electrode. The LTEIGBT was designed so that the width of the device was no more than 19 µm. The latch-up current densities of LIGBT, LTIGBT and LTEIGBT were 120 A/cm2, 540 A/cm2, and 1230 A/cm2, respectively. The enhanced latch-up capability of the LTEIGBT was obtained due to the holes in the current directly reaching the cathode via the p+ cathode layer underneath the n+ cathode layer. The forward blocking voltage of the LTEIGBT was 130 V. Those for conventional LIGBT and LTIGBT of the same size were no more than 60 V and 100 V, respectively. Because the proposed device was constructed of trench-type electrodes, the electric field moved toward the trench-oxide layer, and punch-through breakdown of LTEIGBT occurred late.
Thermal Stability and Electrical Properties of SrBi2Ta2-xNbxO9/IrOx Capacitors with Pt Top Electrode
Authors: Kweon Soon Yong , Choi Si Kyung , Yang Woo Seok , Yeom Seung Jin , Roh Jae Sung
Published: October 2002

Both SrBi2Ta2-x
Nb
x
O9 (SBTN) film and IrO
x
electrode were used for fabricating a capacitor of high-density ferroelectric random access memory. IrO
x
was deposited by reactive sputtering, and the spin-on technique was used for coating the SBTN layer. Marked evaporation was observed in 2000-Å-thick IrO
x
film after electrode annealing at temperatures above 700°C. The evaporation was caused by the reduction of IrO
x
to metallic iridium. However, SBTN/IrO
x
stack remained stable even after annealing up to 800°C. Ferroelectric crystallization annealing during the integration was performed at 650°C for the application of stacked capacitor architecture. Thus, the Pt/SBTN/IrO
x
capacitor could be fabricated up to metallization without damaging the microstructure. The switching polarization was about 10 µC/cm2 at the 2.4 µm×3.7 µm×256 ea array capacitor after metallization and the leakage current density was about 4×10-7 A/cm2. The contact resistance of the SBTN/IrO
x
/Ir/TiN/plug was about 1500 Ω/plug at the contact size of φ 0.30 µm.
Quantitative Investigation of Hot Carrier Induced Drain Current Degradation in Submicron Drain-Engineered Metal-Oxide-Semiconductor Field-Effect-Transistors
Authors: Yang Jiuun-Jer , Chung Steve Shao-Shiun
Published: October 2002

Parameters, such as the total amount of hot carrier induced interface states and substrate current, are not sufficient to evaluate hot carrier reliability in drain-engineered metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this paper, for the first time, the distributions of hot carrier induced interface states are physically characterized and incorporated into two-dimensional device simulation to quantitatively study the structure-dependent drain current degradation in submicron MOSFETs, which give us insight into the relationship between degradation modes and device structures. The results show that the hot carrier induced series resistance effect in the sidewall spacer region plays an important role in drain-engineered MOSFETs. A different gate oxide thickness dependence of drain current degradation in thin gate oxide lightly-doped drain (LDD) MOSFETs is observed and is explained as the interface states enhanced series resistance effect in the LDD region.
Low-Frequency Noise in Si1-xGex p-Channel Metal Oxide Semiconductor Field-Effect Transistors
Authors: Tsuchiya Toshiaki , Matsuura Takashi , Murota Junichi
Published: October 2002

Low-frequency noise (LFN) in Si1-x
Ge
x
p-channel Metal Oxide Semiconductor Field-Effect Transistors (pMOSFETs) with a relatively wide range of Ge fraction x=0.2, 0.5, 0.7, and Si1-x
Ge
x
thickness d
SiGe of 2–14 nm are investigated. Although LFN of Si1-x
Ge
x
pMOSFETs seems to be complicated functions of d
SiGe and Ge fraction, it is shown that LFN in Si1-x
Ge
x
pMOSFETs can be lower than that in conventional Si pMOSFETs. Moreover, in order to evaluate the trap density at the Si1-x
Ge
x
/Si heterostructure interface, the noise power at bias conditions showing the maximum transconductance g
mMAX is examined. At the bias conditions, drain current is confirmed to flow mainly in the buried Si1-x
Ge
x
channel, but not in the surface Si channel. Surface generation current is also examined to evaluate the trap density at the interface between the gate oxide and the Si capping layer. The dependence of the noise power on d
SiGe and Ge fraction corresponds well to that of g
mMAX, but not to that of the surface generation current. It is concluded that the noise characteristics at the g
mMAX bias conditions reflect the trap density at the Si1-x
Ge
x
/Si heterostructure interface, and correspond well to g
mMAX behavior.
Effects of Rapid Thermal Annealing after Plasma H2 Pretreatment of the Copper Seed Layer Surface on Copper Electroplating
Authors: Oh Junhwan , Lee Hanseung , Paul Avijit , Lee Chongmu
Published: October 2002

In ULSI fabrication, copper is widely accepted as a new interconnect material to replace aluminum and its alloys due to its low resistivity and high electromigration resistance. Cu seed layers for copper electroplating were deposited by magnetron sputtering on silicon wafers using TaN as diffusion barriers between the seed layer and silicon. Effects of plasma H2 pretreatment and also the combined effects of plasma H2 pretreatment and rapid thermal annealing of the Cu seed layers have been investigated on the physical properties including the resistivity, the grain size and the surface roughness of the electroplated copper films. The best physical properties were obtained for the electroplated copper film on the TaN film the surface of which was given the plasma H2 treatment at the rf-power of 100 W for 10 min followed by rapid thermal annealing at 350°C for 30 s. The mechanism of the cleaning process has also been discussed.
A Comparative Study between Total Thickness Variance and Site Flatness of Polished Silicon Wafer
Authors: Oh Han-Seog , Lee Hong-Lim
Published: October 2002

Monocrytalline silicon wafers of wide range of total thickness variance (TTV) were produced and evaluated. Site total indicator readings (STIR) with different reference plane-site front least square focal plane range (SFQR) and site back ideal focal plane range (SBIR) were compared with TTV. SBIR was found to be correlated with TTV but not correlated with SFQR. This result indicates that process development procedure should be separately considered for SBIR and SFQR, respectively.
Gamma-Ray Induced Deep Electron Traps in GaInP
Authors: Sung Wei-Jer , Liu Tong-Yuan , Yang Su-Lin , Huang Kai-Feng , Tseng Tseung-Yuen , Chou Fong-In , Wei Yuan-Yaw , Wu Yu-Rue
Published: October 2002

Deep electron traps created by gamma-ray irradiation of Au/GaInP Schottky diodes grown by metal-organic chemical vapor deposition (MOCVD) were studied by using deep level transient spectroscopy (DLTS) technique. Three distinct deep electron traps, G1, G2 and G3, were observed in the irradiated GaInP samples. According to the analysis of trap properties in various samples, trap G1 is verified as a bulk defect located at 0.13 eV below the conduction band, while trap G2 and G3 are interface states originated from the junctions of Au/Te-doped GaInP contacts.
Extracting the Oxide Capacitance Using Inductance–Capacitance–Resistance Meter Measurement on Metal-Oxide-Semiconductor Capacitors
Authors: Lee Woohyung , Shin Jeshik , Yang Hyundoek , Hwang Hyunsang
Published: October 2002

A new oxide thickness analysis method is proposed which is based on the mode transformation of experimental capacitance–voltage (C–V) data measured in the parallel and series modes. Although the samples exhibited high leakage current, we were able to extract the intrinsic oxide capacitance which was confirmed by quantum mechanical simulation.
Resist Lithographic Performance Enhancement Based on Solvent Removal Measurements by Optical Interferometry
Authors: Raptis Ioannis
Published: October 2002

Post apply bake (PAB) effect understanding and control resulting to enhanced lithographic performance of two negative chemically amplified resists is demonstrated. This study is based on the measurement of the minimum time needed for the removal of the remaining after spin coating solvent using a novel interferometer tool. In the materials examined the free volume enhances the developer selectivity resulting to higher resolution and significantly improved process latitude.
Development of Micro-Optics Using Total Internal Reflection for an Optical Tracking Sensor
Authors: Sakamoto Masahiko , Kawano Hiroyuki
Published: October 2002

A compact and lightweight optics that can be used as an optical tracking sensor for a large capacity floppy disk drive (FDD) is proposed. The developed micro-optics is featured with three points in construction. One is the total internal reflection (TIR) in the substrate which requires no coating material. Another is a refraction-type aperture which eliminates the unnecessary light. The last is a Fresnel lens with a blazed relief structure which realizes high diffraction efficiency. The optics is made of plastic molding that is suitable for mass production. The aperture and Fresnel lens patterns on the molding die can be easily fabricated by machining.
Performance of Ge–Sb–Bi–Te–B Recording Media for Phase-Change Optical Disks
Authors: Lee Chain-Ming , Yen Wen-Shin , Liu Ren-Haur , Chin Tsung-Shune
Published: October 2002

We investigated the physical properties of GeSbBiTeB materials and examined the feasibility for phase change recording. The studied compositions were Ge4Sb0.5Bi0.5Te5 and Ge2Sb1.5Bi0.5Te5 with B doping. The coexistence of Bi and B atoms into both Ge4SbTe5 and Ge2Sb2Te5 lattice maintains single fcc structure without phase separation. The Bi substitution shows benefits in decreasing crystallization temperature and activation energy, however the reflectivity is slightly reduced. [rf3] With small amount addition of boron about 1 at.%, the reflectivity can be increased. [rf2] Conventional 4-layer structure of digital versatile disk-random access memory (DVD-RAM) 2.6 GB format was used to prepare the disks for dynamic characterization and overwrite cyclability evaluations. The disk with Ge4Sb0.5Bi0.5Te5(B) recording layer shows large noise fluctuation and low overwrite erase ratio, suggesting that the crystallization speed is still insufficient. While the disk with Ge2Sb1.5Bi0.5Te5(B) recording layer shows lower writing and erasing powers, stable noise level and high overwrite erase ratio, indicating the capability for DVD-RAM applications. The effect of B doping was verified to enhance the signal amplitude and modulation.
Pulsed Laser Deposition of TiNi Thin Films at Various Temperatures
Authors: Lu Yong-Feng , Chen Xiao-Yu , Ren Zhong-Min , Zhu Sha , Wang Jian-Ping , Liew Thomas Y. F.
Published: October 2002

Thin films of TiNi shape memory alloy (SMA) have been prepared by pulsed-laser deposition (PLD) at various substrate temperatures. X-ray photoelectron spectroscopy (XPS), surface profile measurements, and X-ray diffraction (XRD) are used to characterize the deposited films. The stoichiometry, deposition rate, and crystallinity of the films are investigated as functions of the substrate temperature. The deposition rates are of the order of 10-2 nm per pulse. The Ni content ranges from 46.7 to 52.0 at.%. It is found that the film deposited at a substrate temperature of 600°C has a polycrystalline structure and austenite is the major phase. It can be concluded that substrate temperature plays an important role in the composition control and the crystallization of the films. The martensitic transformation temperature of the annealed Ti–51.5 at.% Ni thin film is determined to be -20.8°C by differential scanning calorimetry (DSC).
Stable Servo System of Digital Versatile Disk Player against Defects
Authors: Ryu Tomoaki , Yokoyama Eiji , Ogawa Masaharu , Kime Kenjiro
Published: October 2002

In this paper, a method for improving the tracking a servo performance at damaged portions of a digital versatile disk (DVD) disk of a DVD player, is presented. In this study, disturbance due to detection delay at the defective portion, one of the causes of degraded tracking servo performance at the defective portion is considered, and the double impulse method to negate the influence of disturbance on the tracking actuator is presented.
Photoluminescence and Electroluminescence Characteristics of New Disubstituted Polyacetylenes
Authors: Ting Ching Hua , Hsu Chain Shu
Published: October 2002

Three di-substituted acetylenes in the tolane structure, 4-(trans-4-pentylcyclohexyl)-3′,4′-difluorotolane (1M), 4-(trans-4-heptylcyclohexyl)-4′-fluorotolane (2M), and 4-(4-pentylphenyl)-4′-fluorotolane (3M), were polymerized in the presence of TaCl5-based catalyst. The weight-average molecular weights \overlineMw of the polymers were high than 4×105. Photoluminescence (PL) and electroluminescence (EL) of the three polymers made as single-layer device on indium-tin oxide glass (ITO), ITO/polymer/Al, have been comprehensively studied. By changing the structural conditions of polymer, such as introducing the fluorine atom or a long carbon chain to the end group of polymer side chains, the luminescence is clearly enhanced.
Photocarrier Transport in Regioregular Poly(3-octadecylthiophene)
Authors: S. Pandey Shyam , Wataru Takashima Wataru Takashima , Koichi Rikitake Koichi Rikitake , Takeshi Endo Takeshi Endo , Masahiro Rikukawa Masahiro Rikukawa , Keiichi Kaneto Keiichi Kaneto
Published: October 2002

Charge carrier transport in regioregular poly(3-octadecylthiophene) has been studied by the time-of-flight method. The nature of transient photocurrent response is dispersive and holes were found to be the majority photocarriers with no detectable signal for electron transport. The hole mobility at room temperature and at an applied field of 1.3 ×105 V/cm has been measured to be 2.5 ×10-5 cm2/V.s. Analysis of the transport mechanism confirms the predictions of the stochastic model of Scher and Montroll as indicated by the universal-scaling behavior of transient photocurrents when they were normalized with respect to transit time. The field and temperature dependence of hole mobility has been analyzed in terms of Poole-Frenkel and Bässler's Gaussian disorder model. The interpretation of the results of hole mobility measurement is made in terms of the concept of hopping among the polymer segments featuring a Gaussian distribution of energies with its variance of 74 meV.
Spatial Distribution of Complex Refractive Index Change in Guest–Host Liquid Crystals Determined by a Phase-Sensitive Interferometric Method
Authors: Hiroshi Ono Hiroshi Ono , Hajime Saeki Hajime Saeki
Published: October 2002

The spatial distributions of the complex photothermal refractive index change in the guest-host liquid crystals were determined by a phase-sensitive optical interferometric method using a Mach-Zehnder interferometer. The Gaussian profile of the pump laser beam reflects the spatial distribution of the laser-induced index change and the radius of the distribution was slightly larger than that of the intensity distribution of the pump beam. In addition, the radius of the distribution of the extraordinary index change is larger than that of the ordinary one. The real part of the extraordinary refractive index change was negative, while that of the ordinary one was positive. Although the absorption coefficient was negligibly small at the wavelength of the probe laser beam, the imaginary part could not be ignored. The imaginary parts of both the extraordinary and ordinary indices changes were negative. These results can be explained by the photothermal effects of the guest-host liquid crystal.