bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Barrier Growth Temperature on the Properties of InGaN/GaN Quantum Well
Authors: Wen Tzu-Chi , Lee Wei-I
Published: October 2002

In this study we investigate the effect of barrier growth temperature on the properties of InGaN/GaN multiple quantum wells. Double-crystal X-ray diffraction of MQW structures indicates that increasing the barrier growth temperature will reduce the well thickness. However, the photoluminescence peak wavelength shift is greater than the change of in the effective bandgap due to the reduction of well width. In addition to the reduction of well width, the determination of the origin of the significant blue shift in the photoluminescence peak wavelength should also take the strain effect into account.
Temperature Dependence of Two Beam Coupling, Light-induced Erasure Decay and Dark Decay in As-Grown and Reduced BaTiO3:Rh
Authors: Chang Jenq-Yang , Huang Chi-Yi , Chu Chen-Fu , Wang Je-Min , Sun Ching-Cherng
Published: October 2002

Two beam coupling, light-induced erasure decay and dark decay are investigated in as-grown and reduced BaTiO3:Rh as a function of temperature. The photorefractive sensitivity increases with temperature, mainly due to the increase of the speed. As deduced from the dark decay measurement, the shallow trap effect decreases while the dark conductivity increases with increasing temperature. These two factors determine how the two beam coupling gain depends on intensity and the intensity dependence power coefficient with response time varies as temperature increases. For the as-grown sample, the photorefractive properties are controlled by the competition between deep and shallow levels when the temperature is below 60°C. Above 60°C, large dark conductivity plays a dominant role. For the sample reduced at an atmosphere of 10-10 atm oxygen partial pressure, the photorefractive properties are controlled by the competition between deep and shallow traps from room temperature to 100°C. For the sample reduced at an atmosphere of 10-14 atm oxygen partial pressure, the photorefractive properties are mainly dependent on the dark conductivity though it has a high photoconductivity.
Microchannel Epitaxy of GaAs from Parallel and Nonparallel Seeds
Authors: Huang Weidong , Nishinaga Tatau , Naritsuka Shigeya
Published: October 2002

We have investigated the lateral coalescence in microchannel epitaxy (MCE) of GaAs from parallel and nonparallel seeds by liquid phase epitaxy (LPE). It was shown that when parallel seeds were employed, the lateral coalescence of the MCE islands started from two points and then preceded inward, but when nonparallel seeds were employed, the lateral coalescence started from one point. The coalesced MCE islands were etched by molten KOH and it was found that when the parallel seeds were employed, dislocation was generated at the last coalesced point in the coalesced region. However, dislocation did not appear in the coalesced region obtained from nonparallel seeds. It is concluded that by employing MCE from nonparallel seeds, one can avoid the formations of dislocations in the coalesced region.
Application of an Electron-Tube Technique to the VENUS Vertex Chamber
Authors: Ohama Taro
Published: October 2002

This paper presents a new method to design and analyze drift chambers which are commonly used in high-energy physics experiments. The method is based on an analogy of the electron-tube theory; in particular, it treats the drift chamber with a grid wire plane as a “triode ion tube” filled with a gas. This method provides an analytical way in which to calculate the potential and/or charge of electrodes (wires) and the electric fields between them. The method also gives a semianalytic means to derive “X–T” relations in a chamber, and to calculate expected signal forms. This method has been developed specifically for designing a vertex chamber installed in the VENUS detector at the TRISTAN e
+
e
- collider. The anode signal forms actually obtained by the VENUS vertex chamber are found to agree well with the predictions by this method.
Inductively Coupled Plasma Source with Internal Straight Antenna
Authors: Kanoh Masaaki , Suzuki Keiji , Tonotani Jyunichi , Aoki Katsuaki , Yamage Masashi
Published: October 2002

An inductively coupled plasma source with an internal straight antenna was developed. By inserting an antenna into plasma, the induction of a strong electric field in the plasma and the efficient transmissions of power to plasma is enabled. However, there was a practical problem in that antenna sputtering occurred. Suppression of antenna sputtering and methods of insulating the antenna were studied. Consequently, it was found that sputtering impurities were reduced by covering the straight antenna with a quartz pipe. Furthermore, the amount of quartz pipe etching could be reduced to as little as 1/10th the original value. As a result of fabricating and evaluating the plasma source in which four straight antennas were arranged in parallel, electron density was determined to be as high as 1011 cm-3 even at a pressure as low as 4 mTorr. When the processing performance of the plasma source was evaluated, the ashing rate of the photoresist and the etching rate of the poly-Si were, respectively, 4.8 µm/min and 450 nm/min. These values are at practically applicable levels.
Multiple-Fiber Collection System for Scanning Tunneling Microscope Light Emission Spectroscopy
Authors: Ryuichi Arafune Ryuichi Arafune , Kenji Sakamoto Kenji Sakamoto , Kazuyuki Meguro Kazuyuki Meguro , Minoru Satoh Minoru Satoh , Atsushi Arai Atsushi Arai , Sukekatsu Ushioda Sukekatsu Ushioda
Published: October 2002

We have constructed an optical fiber system for collecting light emission (LE) from the gap between a sample and the tip of a scanning tunneling microscope (STM). The collection system consists of four optical fibers with a core diameter of 600 µm and a numerical aperture (NA) of 0.2. The four optical fibers point radially at the tip-sample gap from four directions. To demonstrate the performance of the collection system, we evaluated its effective solid angle of collection by measuring the STM-LE from a Au evaporated film. The effective solid angle was estimated to be 0.33±0.03 sr, which corresponds to about 2.6 times that of a single optical fiber determined by the NA (0.13 sr). Although the solid angle of collection did not increase by a factor of four, the increase of the collection solid angle will improve the detection limit by reducing the accumulation time for spectral measurements.
Photolithography and Selective Etching of an Array of Surface Mount Device 32.768 kHz Quartz Tuning Fork Resonators: Definition of Side-Wall Electrodes and Interconnections Using Stencil Mask
Authors: Lee Sungkyu
Published: October 2002

In the present research, both negative (additive) and positive (subtractive) photolithographies were employed to fabricate quartz tuning forks with a resonance frequency (f
R) close to 31.964 kHz and a crystal impedance (C.I.) value of 48 kΩ. The side-wall electrodes and interconnections of quartz tuning forks were subsequently defined by oblique evaporation of a nickel–chromium alloy/gold coating using a stencil mask. The assembled tuning forks were evaluated to measure resonance frequency and crystal impedance values with vacuum levels of the work chamber. The effect of an oblique evaporation angle on electrical characteristics of the tuning forks was studied.
Quantum Mechanical Influence on Flat-Band Capacitance in Metal-Oxide-Semiconductor Structures with a Nanometer-Thick Silicon Oxide Film and the Impact of Oxide Charge Evaluation
Authors: Shimizu Akira , Nakatsuji Hiroshi , Omura Yasuhisa
Published: October 2002

In this paper, we describe theoretically how the quantum-mechanical carrier distribution in the flat-band condition influences the flat-band capacitance. It is numerically demonstrated that the semiclassical method overestimates the flat-band capacitance when the quantum-mechanical effect is significant. It is also shown that the quantum-mechanical flat-band capacitance at the gate poly-Si/SiO2 interface significantly influences the total flat-band capacitance and oxide charge evaluation.
Ferroelectricity in Li-Doped ZnO:X Thin Films and their Application in Optical Switching Devices
Authors: Nagata Takahiro , Shimura Tamaki , Nakano Yoshiyuki , Ashida Atsushi , Fujimura Norifumi , Ito Taichiro
Published: October 2002

We have proposed the application of ZnO:X (X=Li,Ni,Al etc.) films in monolithic optical integrated circuits (OICs). [rf1] To realize the optical switching device, dielectric properties of ZnO:Li deposited on SiO2/p-Si were evaluated in detail. From the results of the frequency dependence of the dielectric permittivity and the loss, and the temperature dependence of ac conductivity at various frequencies, the existence of mobile Li ion was confirmed. The pulsed C–V measurements [rf2] revealed that not only the mobile Li ion but also the ferroelectricity of ZnO:Li contributed to the hysteresis in the normal C–V behavior. To determine the processes assumed to occur in the switching device structure, a prototype of the waveguide structure was fabricated. Although the relationship between the refractive indices of the core and clad layers satisfied the required condition for propagation, several processes such as interdiffusion of doped ions, band alignment and/or rearrangement of space charge when applying the bias voltage were also revealed.
Generation and Dynamic Behaviors of Oxygen Vacancies in Barium Strontium Titanate Ceramics
Authors: Fukami Tatsuo , Agawa Daisuke , Bamba Noriko
Published: October 2002

Oxygen vacancy behaviors in Ni-doped barium strontium titanate (BST) ceramics have been observed through thermally stimulated current (TSC) measurements up to 200°C. The set of observations confirmed that the vacancies drift due to a high electric field at an elevated temperature to pile up under the cathode electrode and the initial complex defects of acceptor, NiTi
′′, and donor, VO
••, are separated from each other forming a forward-biased pn junction. It is also revealed that the oxygen vacancies are newly generated at the anode area either if the ceramic surface is roughened or if a catalytic electrode such as Pt is attached.
Effect of Electrode Materials on Lead Lanthanum Zirconate Titanate with Heating under Reduced Atmosphere
Authors: Kondo Masao , Maruyama Kenji , Kurihara Kazuaki
Published: October 2002

To understand the ferroelectricity degradation of ferroelectric random access memory (FeRAM) capacitor under hydrogen atmosphere, reactions between lead lanthanum zirconate titanate (PLZT) and the electrode materials, such as platinum (Pt) and iridium oxide (IrO2), were investigated by thermal analysis. The PLZT powder was decomposed by heating under Ar+3%H2 atmosphere at 1000°C with lead (Pb) metal, PbO, ZrTiO4 and TiO2. The decomposed PLZT with Pb metal exhibited perovskite phase after annealing under air atmosphere at 1000°C and no pyrochlore phase was observed. We found that Pt reacted with the Pb precipitated from PLZT by heating under Ar+3%H2 atmosphere. Consequently, a large amount of PbPt alloy and a small amount of PtPb4 alloy were formed. The formation temperature of the alloys was lower than the decomposition temperature of PLZT without Pt. Pt was directly involved in the decomposition of PLZT. However, no alloys of Ir and Pb were formed in the mixture of PLZT and IrO2 under Ar+3%H2 atmosphere. The heat treatment of the mixture of PLZT and the electrode powders indicated that Pt promoted the decomposition of PLZT under Ar+3%H2 atmosphere and IrO2 reduced the rate of the decomposition.
Selective Area Mass Transport Regrowth of Gallium Nitride
Authors: Heikman Sten , DenBaars Steven P. , Mishra Umesh K.
Published: October 2002

Selective area mass transport regrowth of GaN was performed on wafers with etched wells and SiO2 mask. The samples were annealed in NH3 and H2 flow, with no gallium precursor. At 1060°C, only little mass transport occured, but the sidewall morphology changed, depending on crystallographic orientation. At 1160°C, the sidewalls grew out about 1 µm in 1 min, independent of orientation. The technique can potentially be performed in an annealing chamber, providing a low cost regrowth process. A promising application is ohmic contact regrowth to high composition AlGaN/GaN high electron mobility transistors.
Thermodynamic Consideration for Photoinduced Surface Deposition of Ag–As–S Glasses
Authors: Kawaguchi Takeshi
Published: October 2002

Thermodynamic aspects of the photoinduced surface deposition (PSD) phenomenon have been investigated to reveal the compositional dependence of the PSD effect and its irreversibility. The free energy of the (Ag2S)
y
(AsS)1-y
quasibinary system was calculated as a function of Ag content. The thermodynamic problems concerning the PSD phenomenon in Ag–As–S glasses can be solved based on the free energy of the quasibinary system.
Crystal Growth and Characterization of Lanthanum Substituted Bismuth Titanate Single Crystals
Authors: Aoyagi Rintaro , Takeda Hiroaki , Okamura Soichiro , Shiosaki Tadashi
Published: October 2002

The thermostability of lanthanum substituted bismuth titanate, Bi4-x
La
x
Ti3O12 (BLT), with La-content up to x=0.75 was investigated using differential thermal analysis. Subsequently, BLT and Bi4Ti3O12 (BIT) single crystals were grown by a self-flux method. The BLT crystals with two different ranges of La content, x=1.0–1.5 and 0<x<0.1, were obtained using starting materials with mole ratio BLT(x=0.25):Bi2O3=1:9. Segregation phenomena of La during crystal growth process were observed. A comparison of dielectric and ferroelectric properties in BIT and BLT crystals was performed. The La incorporation led to a significant increase in the coercive field value, E
c, of BIT single crystals.
Preparation of Ferroelectric Thick Film Actuator on Silicon Substrate by Screen-Printing
Authors: Futakuchi Tomoaki , Yamano Hiroshi , Adachi Masatoshi
Published: October 2002

Piezoelectric actuators were prepared on Si substrates that have membranes fabricated by the wet-etching process. Ferroelectric Pb[Zr0.2 Ti0.3(Mg1/3 Nb2/3)0.3(Zn1/3 Nb2/3)0.1(Mg1/2W1/2)0.1]O3 thick films with a thickness of 25 µm, and Pt bottom electrodes and Ag top electrodes were all prepared by screen printing methods. The actuation properties were investigated for an actuator with the dimensions of 3×10 mm2. The influence of membrane's thickness was examined. The displacement of the center of the actuator with a 100-µm-thick membrane was 0.3 µm at an applied voltage of 25 V. An array of micro actuators with the dimensions of 0.15×5 mm2 were also successfully prepared by screen-printing.
Piezoelectric Properties of Bi3TiNbO9–BaBi2Nb2O9 Ceramics
Authors: Nanao Masaru , Hirose Masakazu , Tsukada Takeo
Published: October 2002

Piezoelectric properties of lead-free bismuth layer structure oxides, (1-x)Bi3TiNbO9 (BTN)–xBaBi2Nb2O9 (BBN) (m=2) ceramics, have been studied. We have observed large piezoelectric properties for x values between 0.1 and 0.3. Within this range of x values, these specimens have an orthorhombic structure, high anisotropy of the a and b axes and high resistivity. Also, for these samples, a large coercive force (E
c) of 8.0 kV/mm, large remanent polarization (P
r) of 7.1 µC/cm2 at 200°C and high Curie temperatures (T
c) of 700–900°C have been obtained. Maximum mechanical quality factor (Q
m) of 9000 at 16 MHz thickness extensional third vibration mode (TE3rd) has been measured.
Preparation of Texture-Controlled Lead Zirconate Titanate Diaphragm-Type Film Actuator Using a Chemical Solution Method
Authors: Iijima Takashi , Kunii Kouki
Published: October 2002

A diaphragm-type (100)-dominant-oriented tetragonal phase lead zirconate titanate (PZT) film actuator was fabricated. The ferroelectric properties of the texture-controlled PZT film were comparable to those of bulk PZT ceramics. The displacement property of the PZT film actuator driven at ±20 V exhibited a butterfly-like hysteresis. However, this butterfly shape showed an opposite direction to that of the typical displacement curve of bulk PZT ceramics. This depressed displacement property of the PZT film appears to indicate bend motion in the vertical direction on the film surface since the film is not clamped, and it does not reflect the genuine piezoelectric property. For a unipolar drive, the value of the displacement was about 220 nm at 20 V. The deflection amplitude of the diaphragm actuator showed a peak at 77.5 kHz. Therefore, the diaphragm of the texture-controlled PZT film is considered to be applicable to microactuators.
Rotary Multilayer Split Morph–A Piezoelectric Microactuator for Dual-Stage Actuation Systems in High Track Density Hard Disk Drives
Authors: Wang Zhihong , Zhu Weiguang , Tan Ooi Kiang , Yao Xi
Published: October 2002

A novel annular rotary piezoelectric microactuator has been proposed for a dual-stage actuation system for future high track density hard disk drives. The microactuator is designed to be mounted on a flexure tongue and drives a slider directly to perform high-frequency track following. The configuration and operation of the microactuator are described. The controllable stroke and the resonance frequency of the slider/actuator assembly have been evaluated and optimized by finite-element analysis. The results reveal that the designed actuator/slider assembly should be a promising addition to the dual-stage actuation system.
The Study on Ferromagnetic Resonance Linewidth for NM/80NiFe/NM (NM=Cu, Ta, Pd and Pt) Films
Authors: Shigemi Mizukami Shigemi Mizukami , Yasuo Ando Yasuo Ando , Terunobu Miyazaki Terunobu Miyazaki
Published: October 2002

The out-of-plane angular dependence of ferromagnetic resonance (FMR) was measured for NM/80NiFe(Py)/NM (NM=Cu, Ta, Pd and Pt) films with various Py, Cu and Ta thicknesses fabricated by magnetron sputtering. The out-of-plane angular dependences of FMR resonance field and linewidth were analyzed using Landau-Lifshitz-Gilbert equation taking account of broadening of linewidth due to magnetic inhomogeneities in a film. Magnetic inhomogeneities were assumed to be the fluctuation of magnitude and direction of the effective demagnetization field which contains both demagnetization and perpendicular anisotropy field for a film. The calculations of the angular variations of linewidth agreed with the experimental ones quantitatively. The fluctuations of magnitude and direction of the effective demagnetization field, which are represented as Δ(4πM
eff.) and Δθ
H
, respectively, increased with decreasing Py thickness for all NM/Py/NM films. Δθ
H
increased as the thicknesses of the buffer layers increased for Cu/Py(40 Å)/Cu films and was almost constant with increasing buffer layer thickness for Ta/Py(40 Å)/Ta films. Only in the case of NM=Pd and Pt films, the Gilbert damping parameter, which is the speed of decay of magnetization precession, was enhanced significantly as compared with that for the bulk sample and was dependent on Py thickness.
Relationship between Lattice Deformation and Polarization in BaTiO3
Authors: Hiromu Miyazawa Hiromu Miyazawa , Eiji Natori Eiji Natori , Tatsuya Shimoda Tatsuya Shimoda , Hiroki Kishimoto Hiroki Kishimoto , Fumiyuki Ishii Fumiyuki Ishii , Tamio Oguchi Tamio Oguchi
Published: October 2002

The relationship between lattice deformation and electrical polarization in tetragonal BaTiO3 is investigated. The density functional theory within the local density approximation using the full-potential-linear-augmented-plane-wave (FLAPW) method is adopted to obtain internal atom positions and one-electron wave functions. Electric polarization is calculated using the Berry-phase theory. We have found that a lattice strain of the order of 1% along the c-axis enhances polarization considerably. However, for that of the order of 0.1%, polarization hardly changes. We assume that these responses of the polarization to lattice strain are related to the stress sensitivity of the polarization in ferroelectric-thin films through nanoscale domains, especially ferroelectric-90-degree domains. We have also found that the polarization of BaTiO3 can be scaled linearly by the distance between Ti and its nearest-neighbor oxygen (apical site in oxygen octahedron). This indicates that the covalency between Ti and the apical oxygen is the only driving force for the ferroelectricity in BaTiO3. We suggest that this covalency softens Young's modulus of BaTiO3 in the ferroelectric states compared to the paraelectric states through the increase of the degree of freedom for atomic displacements in a unit cell.
Fundamental Study of Surface Layer on Ferroelectrics by Scanning Nonlinear Dielectric Microscopy
Authors: Ohara Koya , Cho Yasuo
Published: October 2002

Distribution and growth of very thin surface layers on ferroelectric materials are investigated by scanning nonlinear dielectric microscopy. This microscopy technique involves the measurement of higher order nonlinear dielectric constants, with depth resolution down to one unit cell order. By changing the order of nonlinearity of the dielectric response, we obtain information about the surface layer on lead zirconate titanate (PZT) thin film and also observe the growth process of a surface paraelectric layer on LiNbO3 single crystal.
Modelling of Structural and Threshold Voltage Characteristics of Randomly Doped Silicon Nanowires in the Coulomb-Blockade Regime
Authors: Evans Gareth J. , Mizuta Hiroshi , Ahmed Haroon
Published: October 2002

We report on the theoretical investigation of how geometrically uniform highly doped silicon nanowires can break up into a series of islands that exhibit Coulomb blockade. By using a newly developed numerical simulation in which random ionized dopants are introduced explicitly and the electron distribution is calculated self-consistently under the Thomas-Fermi approximation, we demonstrate natural formation of electron islands in the nanowires owing to the random dopant potential. We study the quasi-one-dimensional nature of the electron islands formed in the nanowires. The offset charge effects on the current threshold of the nanowire transistors are then investigated by feeding the derived structural parameters such as inter-island capacitance and tunnel resistance into a Monte Carlo single electron transport simulator. We show that the overall threshold voltage distribution can roughly be described as a two-`macro'-island system despite a complex series of multiple electron islands.
Long-Term Photocapacitance Decay Behavior in Undoped GaN
Authors: Chung Hao-Ming , Pan Yung-Chung , Chuang Wang-Chung , Chen Nie-Chuan , Tsai Cheng-Chung , Lee Ming-Chih , Chen Wen-Hsiung , Chen Wei-Kuo
Published: October 2002

We have measured the dynamic response of the photocapacitance of a Schottky diode made of an undoped GaN epilayer grown by metalorganic vapor phase epitaxy. The measurements were performed after the suspension of a white light for a specified “waiting” time, t. The results indicate that the capacitance exhibits a logarithmic function of t from which a time constant of approximately 34.5 s and a cross-sectional area of less than 2.89 ×10-27 cm2 were retrieved. These are interpreted as the characteristic time and the cross-sectional area of electron capture by the traps associated with dislocations formed in the epifilm, respectively.
Thickness and Stress Polarity Effects on the Reliability of the Low Thermal Budget Polyoixdes
Authors: Chang Kow Ming , Chung Yuan Hung , Chen Hong Yu , Lee Tzyh Cheang , Sun Yong Long
Published: October 2002

In this paper, the thickness and the stress polarity effects on the reliability of the low thermal budget polyoxides are investigated. The polyoxides are prepared by two methods: the low-temperature tetraethylorthosilicate (TEOS) polyoxide deposition and in the rapid thermal chamber in N2O ambient (RTN2O). It is observed that the thinner TEOS polyoxides exhibit higher charge to breakdown (Q
bd) and larger stress polarity effect than those of the thicker TEOS polyoxides. However, for the RTN2O grown polyoxides from 8.5 nm to 12.9 nm, they have the similar values of the Q
bd and the stress polarity effects. The nitrogen atoms incorporated in the RTN2O grown polyoxides may be the reason to this less thickness dependence of the Q
bd. Higher barrier height is also observed for the RTN2O grown polyoxides than that of the deposited TEOS polyoxide to obtain a lower tunneling current under a fixed electric field.
90° Phase-Matching Properties of YCa4O(BO3)3 and GdxY1-xCa4O(BO3)3
Authors: Umemura Nobuhiro , Nakao Hiroshi , Furuya Hiroyuki , Yoshimura Masashi , Mori Yusuke , Sasaki Takatomo , Yoshida Kunio , Kato Kiyoshi
Published: October 2002

YCa4O(BO3)3 has been found to be 90° phase-matchable for type-1 second-harmonic generation at 0.4168 µm along the z-axis at 20°C. The improved Sellmeier equations of YCa4O(BO3)3 that correctly reproduce our new experimental data for second-harmonic and sum-frequency generation in the 0.3547–1.9079 µm range are reported. In addition, the 90° phase-matching properties of Gd
x
Y1-x
Ca4O(BO3)3 as a function of the Gd molar concentration X are presented together with the empirical index formula.
Relationship between Structure and Dielectric Property in (1-x)(Na1/2Bi1/2)TiO3–xPbZrO3 Ceramics
Authors: Lee Jung-Kun , Yi Jae Yun , Hong Kug-Sun
Published: October 2002

The effect that PbZrO3 (PZ) addition to (Na1/2Bi1/2)TiO3 (NBT) has on crystal structure, domain state, ferroelectric property and cation ordering was investigated. With increasing PZ concentration, lattice distortion of NBT decreased and the phase transition behavior became similar to that of relaxor ferroelectrics. The relaxor-like behavior was maximum in a NBT–0.5PZ ceramics, whose phase transition behavior and ferroelectric hysteresis loop were those of typical relaxor ferroelectrics. These variations were discussed in terms of cation ordering and local fields. Structural analysis using transmission electron microscope (TEM) revealed that PZ addition prevented the arrangement of A-site cations, which caused random fields and non-uniform polarization in NBT–PZ solid solution.
Theory of Chaotic Dynamics on Class A Laser with Optical Delayed Feedback
Authors: Kuwashima Fumiyoshi , Kitazima Iwao , Iwasawa Hiroshi
Published: October 2002

Chaotic dynamics of a single-mode class A laser is first investigated theoretically. We derived the equation of the electric field for the single-mode class A laser with optical feedback in which the multireflection effect was taken into account. The stationary solution and its stability were considered analytically, and the dynamics were studied by numerical analysis. The results of the simulations were given in time series, phase portraits, bifurcation diagrams, and the Lyapunov exponents, and the threshold value of feedback rate a for chaos, the route to chaos, and also the multireflective effects were discussed. These results agreed qualitatively with the experimental results as shown in our previous paper [Jpn. J. Appl. Phys. 38 (1999) 6321]. It is notable that the time behavior often presented phenomena similar to low-frequency fluctuation (LFF) as already observed in semiconductor lasers.
R-Dependency of the Hardness of Perovskite-Type RRh3B Compounds (R = La, Gd, Lu and Sc)
Authors: Shishido Toetsu , Kudou Kunio , Okada Shigeru , Ye Jinhua , Yoshikawa Akira , Sasaki Takahiko , Oku Masaoki , Horiuchi Hiroyuki , Higashi Iwami , Kohiki Shigemi , Kawazoe Yoshiyuki , Nakajima Kazuo
Published: October 2002

Perovskite-type rare-earth rhodium borides of the chemical formula RRh3B (R=La, Gd, Lu and Sc) have been studied from the viewpoint of microhardness. Polycrystals of RRh3B are synthesized by the arc melting method. RRh3B compounds have a perovskite-type cubic structure (space group: P
m3m). The microhardness become larger with the contraction of the volume of the Rh6B octahedron in the perovskite-type structure. As a result, microhardness increases with decreasing atomic size of R in RRh3B.
Dielectric Response and dc Conductivity in Polyvinylbutyral: An Analysis in the Complex Conductivity Plane
Authors: Santos Simón , Salazar Iris , Gómez Catalino
Published: October 2002

Dielectric measurements have been carried out on thin films of polyvinylbutyral in the frequency range from 10 to 105 Hz at room temperature. The response was analyzed in terms of a graphical representation in the complex conductivity plane. Using this representation, a value of the contribution of dc conductivity on the order of 1.05×10-10 S/m was estimated. This value was of the same order as that obtained by complementary current-voltage measurements. The similarity between these two values is an indication that in our samples, the contribution to the dc and ac conductivities stems from conduction mechanisms of different origins, which confirms that in polar polymers these two contributions can be experimentally separated, since the dipoles do not contribute to the conduction current. The same behavior was observed at different temperatures. These results allow us to conclude that the representation of dielectric data in the conductivity complex plane provides an alternative to estimating the contribution of a dc conductivity from the dielectric response, without the experimental complication of measurements at extremely low frequencies.
Defect Structure of Heteroepitaxial SnO2 Thin Films Grown on TiO2 Substrates
Authors: Wakabayashi Hirotaka , Suzuki Toshimasa , Iwazaki Yoshiki , Fujimoto Masayuki
Published: October 2002

Heteroepitaxal SnO2 thin films were grown on rutile (100) TiO2 single crystal substrates by pulsed laser deposition. The defect structure and surface morphology were investigated by transmission electron microscopy, reflection high-energy electron diffraction, and atomic force microscopy. The misfit-induced large biaxial compressive stress in the 200-nm-thick SnO2 thin film was almost fully relaxed to yield the high-density interfacial misfit dislocations and related planar defects. The misfit dislocation network on the hetero-interface consisted of two types of partial edge dislocations with Burgers vectors of 1/2<101> and 1/2<110>, which involved {101} and {010} planar defects formed in the film, respectively. The evolution of the surface morphology and cross-sectional structure for thinner films suggested that the introduction of such defects occurs at the early growth stage, due to large lattice misfit, and is strongly affected by point defect condensation.
Electron Detachment for Collisions of Intermediate Energy Cu- and Ag- with He
Authors: Li Guang-Wu , Zhang Xue-Mei , Wu Shi-Min , He Mian-Hong , Lu Fu-Quan , Tang Jia-Yong , Peng Xian-Jue , Yang Fu-Jia
Published: October 2002

The total electron detachment cross sections for the collisions of Cu- and Ag- with He have been measured in the range of 10–30 keV by the growth-rate method. The typical value of the cross section at 20 keV energy is 7.63×10-16 cm2 for Cu-, and 6.66×10-16 cm2 for Ag-. The experimental uncertainty of the results is within ±8% in this work.
Effects of Directional Microphone and Transducer in Spatially Feedforward Active Noise Control System
Authors: Wu Jian-Da , Bai Mingsian R.
Published: October 2002

In this paper, an experimental study concerning the effects of a directional microphone and transducer in a duct active noise control (ANC) system in the presence of acoustic feedback is described. In the duct ANC system, a spatial feedforward system is used for broadband noise cancellation in ducts, where a non-acoustical reference is unavailable. In this structure, acoustic feedback that is known to be detrimental to the system stability and performance must be taken into account in the controller design. The algorithm of the proposed control system is based on the previous work by Roure (1985), Munjal and Eriksson, Hong and Bernstein (1998), and there exists some discusses for spatially feedforward structure. The algorithm is implemented on a digital signal processor (DSP), using finite impulse response (FIR) and infinite impulse response (IIR) filters. Experiments are carried out to evaluate the effects of a directional microphone and transducer in proposed the system for reducing the noise at the broadband noise source. The results of the experiment indicated that the proposed system with a directional microphone and loudspeaker improved the ANC system attenuation performance in the presence of acoustic feedback.
Mode Control of Vertical-Cavity Surface-Emitting Lasers by Germanium Coating
Authors: Chiou Shu-Woei , Lin Gray , Lee Chien-Ping , Yang Hung-Pin , Sung Chia-Pin
Published: October 2002

We have successfully developed a selective surface coating technique to control the modal behavior of the ion-implanted vertical-cavity surface-emitting laser (VCSEL). With selective deposition of a germanium coating by the lift-off process, we could spatially control the threshold gain condition of the VCSEL to support the single transverse mode. The threshold current is 7 mA and single transverse mode operation is maintained up to 1 mW. The method is simple and nondestructive compared with other techniques.
Effect of Thermal Annealing on Band Edge Absorption Spectrum of Arsenic-Ion-Implanted GaAs
Authors: Lin Gong-Ru , Pan Ci-Ling
Published: October 2002

We report the effects of annealing temperature on the near-band-gap transmittance, the absorption coefficient, and the evolution of shallow-level defects of arsenic-ion-implanted GaAs (hereafter referred to as GaAs:As+) using Fourier-transform infrared spectroscopy. The maximum above-band-gap transmittance and absorption coefficient are determined to be 0.4 and 6×103 cm-1, respectively. An anomalous absorption peak at the photon energy of 1.37–1.4 eV for the GaAs:As+ samples annealed at lower than 500°C is observed. By either fitting the absorption curve, the band-gap energy of rapid-thermal-annealed GaAs:As+ is evaluated, which blue shifts from 1.36 eV to 1.41 eV as the annealing temperature increases from 300°C to 800°C. The slightly rising absorption spectra at the near-band-gap region suggest the existence of defects and scattering centers. The activation energies and formatting mechanisms of the dense defects in the Rapid-thermal-annealed GaAs:As+ samples were identified. By characterizing the differential absorption spectra, the eVolution of some defect-related absorption bands during the high-temperature annealing process were observed and the correlated structural phenomena were explained.
Comparative Hydrogen-Sensing Study of Pd/GaAs and Pd/InP Metal-Oxide-Semiconductor Schottky Diodes
Authors: Liu Wen-Chau , Pan Hsi-Jen , Chen Huey-Ing , Lin Kun-Wei , Wang Chik-Kai
Published: October 2002

In this work, the hydrogen response characteristics and sensing properties of catalytic Pd metal-oxide-semiconductor (MOS) Schottky diodes based on both GaAs and InP substrates are comparatively investigated. The behaviors of interface Fermi-level pinning causing the apparent difference in the barrier height modulation and the sensitivity are discussed. Furthermore, the effects of temperature and hydrogen concentration in the initial rate of change in current and the response time are examined. In order to study the steady-state reaction kinetics, we also performed the Langmuir analysis to estimate the values of initial heat of adsorption for both devices. Based on the adsorption isotherm of Temkin type, the interface coverage dependent heat of adsorption is responsible for the wide hydrogen sensing range. From the theoretical prediction, both devices have a very low sensitivity limit under atmospheric conditions.
Exchange Coupling Effect in Magnetic Trilayer Systems with Perpendicular Anisotropic Interlayer
Authors: Hu Jing-guo , Jin Guo-jun , Ma Yu-qiang
Published: October 2002

Based on a simple micromagnetic approach, the equilibrium magnetic configuration, the inducing field and the magnetic hysteresis in a trilayer magnetic structure with horizontal-perpendicular-horizontal anisotropy are investigated by both analytical derivation and numerical calculation. It is shown that the equilibrium magnetic configuration, the inducing effect, and the behavior of magnetic hysteresis are all strongly dependent on the thickness of intermediate defect layer, as well as on the applied field. Interestingly, the magnetic hysteresis shows characteristic shape of soft magnet even though the host matrices are composed of hard magnetic materials. Furthermore, the coercive field H
coer always increases with the thickness of interlayer, but does not approach saturation. The results are compared with the previous data reported for a trilayer structure having perpendicular-horizontal-perpendicular anisotropy studied by Yorozu and Hu. The pronounced difference can be found in both circumstances due to the different arrangement of magnetic trilayer systems.
Terahertz Radiation from Superconducting YBa2Cu3O7-δ Thin Films with 1.55 µm Excitation
Authors: Kondo Takashi , Tonouchi Masayoshi , Hangyo Masanori
Published: October 2002

We observed terahertz (THz) radiation from superconducting YBa2Cu3O7-δ (YBCO) thin films excited by femtosecond laser pulses with a center wavelength around 1.55 µm. The THz radiation mechanism is revealed to be a one photon excitation process corresponding to an intraband transition in the in-gap state. The property of the THz radiation excited by a 1.55 µm laser is similar to that excited by an 800 nm laser.
Evaluation of Silicide Morphology by Near-Infrared-Laser Optical-Beam-Induced-Current Technique
Authors: Koyama Tohru , Umeno Masataka , Komori Junko , Mashiko Yoji
Published: October 2002

We found that the near-infrared-laser optical-beam-induced-current (IR-OBIC) technique was very useful for the evaluation of silicide morphology in ultralarge-scale integrated (ULSI) devices. By this technique, it is possible to detect the cohesion points of silicide as two-dimensional images by scanning a near-infrared laser from the back of the chip. The cohesion points appear as bright spots. We confirmed that the number and intensity of bright spots changed according to the extent of cohesion for some different samples upon varying the silicide layer thickness or thermal treatment time after silicide formation. Furthermore, other experiments were performed to clarify the image formation mechanism at cohesion points. It was demonstrated that the electromotive current was generated upon irradiation by the near-infrared-laser, and Schottky junctions were formed at cohesion points. Thus, it was clarified that the images obtained at cohesion points by this technique are a result of the electromotive current generated due to the carriers (electrons or holes) that are excited over the Schottky barrier formed at cohesion points. The IR-OBIC technique can be used to detect the silicide morphology nondestructively without the need to remove the upper layers of the silicide layer. This study reveals a novel application of the IR-OBIC method which is a very useful technique for the evolution of the self-aligned silicide (SALICIDE) process or structure in future ULSIs.
Laser Performance of Neodymium-Doped Lanthanum Tungstate Crystals
Authors: Urata Yoshiharu , Fukuda Tsuguo , Ito Hiromasa , Wada Satoshi
Published: October 2002

We demonstrated the laser oscillation at 1.06 µm with neodymium-doped lanthanum tungstate crystals under pulsed-laser pumping at 802 nm. Fiber-shaped crystals with Nd concentration of up to 20 at.% were grown using the micro-pulling-down method. A maximum slope efficiency of 35% was achieved for a 3.2 at.%-doped sample at 1059 nm.
Origin of Broad Visible Emission from Branched Polysilane and Polygermane Chains
Authors: Watanabe Akira , Sato Takaaki , Matsuda Minoru
Published: October 2002

The emission properties of branched polysilane and polygermane are studied using time-resolved emission spectroscopy. As branched polymers, the organosilicon cluster (OSI) and organogermanium cluster (OGE) are investigated, which are prepared from tetrachlorosilane and tetrachlorogermane, respectively, and have a hyperbranched structure. The broad visible emissions of OSI and OGE are explained by the energy diagram based on a configuration coordinate model, and the excited states are attributed to a localized state around the branching point. The molecular orbital (MO) calculation suggested the formation of a localized state by the distortion around the branching point in the excited state. The potential barrier for the nonradiative relaxation process was determined from the temperature dependence of the emission lifetime.
Temperature Dependence of Time-resolved Photoluminescence in Mercuric Iodide
Authors: Wen Xiao-Ming , Ohno Nobuhito
Published: October 2002

Time-resolved photoluminescence (TRPL) of red mercuric iodide single crystal was measured from 10 K to 110 K. Several near band-gap exciton lines were found in 530 nm and a broad band was found at 630 nm. At near band-gap region photoluminescence comprises fast and slow decay components. Free excitons convert into bound excitons much more efficiently than the bound into the free so that non-radiative decay becomes dominant. At 10 K the dominant decay of bound excitons was radiation. With increasing temperature non-radiative decay became gradually dominant so that luminescent intensity of bound exciton line decreased and lifetime shortened quickly, especially from 20 K to 30 K. The TRPL experiment revealed that 630 nm band originates from the radiative recombination of donor-acceptor pairs. The central wavelength of the band shifted toward shorter wavelength with increasing temperature and the intensity decay can be depicted as t
-n(r). The recombination rate of the donor-acceptor pairs is dependent of wavelength and temperature.
Theoretical Study on the Homeotropic-Transient Planar Transition of Cholesteric Liquid Crystals
Authors: Yang Young-Chol , Lee Min-Hyong , Kim Jae-Eun , Park Hae Yong , Lee Jong-Choen
Published: October 2002

We investigate both analytically and numerically the time evolution of the director field in the homeotropic-transient planar transition of cholesteric liquid crystals bounded by parallel substrates. The analytic solution of approximate dynamic equations shows that, at the initial stages of the transition, the spatial frequency of the director components perpendicular to the helical axis should be smaller than 2(K
22/K
33)q
0, and the growth rate of the components depends on the spatial frequency and the elastic constants of both twist and bend. We find that (K
22/K
33)q
0 is the most probable value considering either thermal agitation of the director or the free energy density as a function of spatial frequency and thermal agitation in the initial stages. Numerical solutions of exact dynamic equations show that the initial spatial frequency remains constant throughout the transition, which indicates that the pitch of the transient planar texture is determined by the initial condition. Functional dependence of the growth rate on the elastic constants quatitatively agrees well with that of numerical solution of exact dynamic equation.
Polarization Switching in Pb(Zn1/3Nb2/3)O3–5%PbTiO3 Crystals
Authors: Lee Jung-Kun , Yi Jae Yun , Hong Kug Sun , Park Seung-Eek
Published: October 2002

The polarization switching mechanism as a function of crystallographic orientation in Pb(Zn1/3Nb2/3)O3–5%PbTiO3 (PZN–5%PT) single crystals was investigated using the switching current measurement technique. Both the activation E-field and the critical pulse width were greater if E-field for polarization switching was applied along the polar axis <111> than applied along <001>. The sideward growth was dominant in domain switching of <111> oriented crystals. The dominance of the nucleation and forward growth behavior was observed in <001> oriented crystals. The nucleation probability of reverse polarized domains is expected to be much greater in <001> crystals than in <111> crystals, being ascribed to the lower projected polarization value along the E-field direction, higher domain wall energy associated with the pseudo-monoclinic structure of domains, and large domain wall density as a consequence of averaged domain configuration. This domain switching anisotropy may be one of the origins of the fatigue anisotropy.
Molecular Orientation Analysis of a Design Concept for Optical Properties of Liquid Crystal Microlenses
Authors: Yanase Satoshi , Ouchi Kazuhiro , Sato Susumu
Published: October 2002

The relationship between a liquid crystal (LC) molecular orientation state and the focusing properties of LC microlenses prepared using a pair of hole-patterned electrodes are studied. In particular, in order to obtain a large optical effect, molecular orientation and retardation distributions in the LC microlenses with a thick LC layer are investigated by experiments and simulations using the finite difference method (FDM). It is found that the LC microlens functions not only as a converging lens at a low applied voltage but also as a diverging lens at a high applied voltage. The focal length of the LC microlens with D/t of 1/1 is shorter than that with 1/2, where D is the pattern diameter and t is the LC thickness. Dependences of the converging and diverging properties on the D/t values are successfully explained by the FDM simulations of the LC molecular orientation. In the case of large D/t values, the middle region of LC layers mainly contributes to the effective refractive index distribution of the LC microlens. On the other hand, the contribution of both surface regions is dominant when D/t becomes small. It seems that the LC molecular orientation outside the circular-pattern affects effectively to that inside the region with decreasing D/t values.
Properties of TiO2 Thin Films on InP substrate Prepared by Metalorganic Chemical Vapor Deposition
Authors: Lee Ming-Kwei , Hung Yi-Min , Huang Jung-Jie
Published: October 2002

The deposition of TiO2 thin films on an InP substrate is studied by metalorganic chemical vapor deposition (MOCVD) in the temperature range of 300–550°C with Ti(i-OC3H7)4 and O2 as the starting materials. The morphology of the TiO2 films is mirror like. The structure, growthrate and grain size of the TiO2 films depend on the deposition temperature. The film stoichometry was measured by energy dispersive X-ray (EDX) spectroscopy. The refractive index of the TiO2 films as measured by ellipsometry reached 2.6 at the growth temperature of 350°C. Based on current-voltage measurement of the Al/TiO2/InP structure, the leakagecurrent is 1×10-5 A/cm2 under the electric field of 0.06 MV/cm at the growth temperature of 500°C.
Morphology of Silicon Oxide Film on Silicon Wafer Surface during Its Removal Process in a Hydrogen Ambient
Authors: Mayusumi Masanori , Imai Masato , Nakahara Shinji , Inoue Kazutoshi , Habuka Hitoshi
Published: October 2002

In order to develop the low-temperature silicon epitaxial growth process, the change in the surface morphology of the silicon dioxide film and the silicon surface is studied in a transient state, for the first time, at 1223 K at a pressure of 40–101 kPa in a hydrogen ambient. A very smooth and clear silicon substrate surface is achieved using a uniform silicon dioxide film formed using ozonated ultrapure water and a very low flow rate of hydrogen gas. The surface morphology of the silicon substrate finally becomes smooth and the pit formation is suppressed, although the surface shows a nonuniform island appearance during the removal of the silicon dioxide film. The microroughness of the silicon substrate surface is improved by heating in a hydrogen ambient and by the silicon epitaxial film growth after complete removal of the ozone oxide film.