Browsing by Issue Date, starting with "2002-08-15"

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Strain-induced semimetal-semiconductor transition in InAs/GaSb broken-gap quantum wells
(2002-08-15)
Zakharova, A
;
Yen, ST
;
Chao, KA
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We investigate the hybridization of the electron, heavy-hole and/or light-hole dispersion relations in strained InAs/GaSb quantum wells. In the considered structures, the lowest electron level lies below several hole levels at zero in-plane wave vector k(parallel to), so that the anticrossings of subbands produce gaps in the in-plane dispersions. To calculate the electronic band structures of such quantum wells grown on different substrates, we use the eight-band k.p model and the scattering matrix method. We have found that the order of levels at the zone center (k(parallel to)=0), gap positions and magnitudes can change due to the lattice-mismatched strain. Strain can also enhance the hybridization of electron and light-hole states at k(parallel to)=0 considerably. In the structure with a thick InAs layer grown on GaSb, we have obtained a negative indirect gap in the in-plane dispersion resulting from the anticrossing of electronlike and highest heavy-hole-like subbands. If the substrate is InAs, the gap becomes direct and positive. This phenomenon can be treated as strain-induced semimetal-semiconductor phase transition.
Stabilization of nonlinear systems in compound critical cases
(2002-08-15)
Liaw, DC
;
Chen, CH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we study the stabilization of nonlinear systems in critical cases by using the center manifold reduction technique. Three degenerate cases are considered, wherein the linearized model of the system has two zero eigenvalues, one zero eigenvalue and a pair of nonzero pure imaginary eigenvalues, or two distinct pairs of nonzero pure imaginary eigenvalues; while the remaining eigenvalues are stable. Using a local nonlinear mapping (normal form reduction) and Liapunov stability criteria, one can obtain the stability conditions for the degenerate reduced models in terms of the original system dynamics. The stabilizing control laws, in linear and/or nonlinear feedback forms, are then designed for both linearly controllable and linearly uncontrollable cases. The normal form transformations obtained in this paper have been verified by using code MACSYMA. (C) 2002 Elsevier Science Inc. All rights reserved.
Dependence of luminescence efficiency on dopant concentration and sintering temperature in the erbium-doped Ba0.7Sr0.3TiO3 thin films
(2002-08-15)
Kuo, SY
;
Chen, CS
;
Tseng, TY
;
Chang, SC
;
Hsieh, WF
We found the dependence of luminescence efficiency on Er3+ concentration and sintering temperature in the Er-doped Ba0.7Sr0.3TiO3 (BST) thin films is governed by crystallinity and ion-ion interaction. X-ray diffraction and Raman studies of the sol-gel prepared samples show that the BST polycrystalline phase occurred when the sintering temperature reaches 700 degreesC, whereas, it becomes worse for temperature above 700 degreesC resulting from phase separation and the Er3+ concentration exceeding 3 mol % due to charge compensation mechanism. The observed green emission reaches maximum at sintering temperature 700 degreesC and 3 mol % Er3+ ions concentration. We also showed the Er dopant does not affect the dielectric property of BST thin films in C-V measurement and the Ba0.7Sr0.3TiO3 films doped with Er3+ ions may have potential use for electroluminescence devices. (C) 2002 American Institute of Physics.
Gallium nitride nanorods fabricated by inductively coupled plasma reactive ion etching
(2002-08-15)
Yu, CC
;
Chu, CF
;
Tsai, JY
;
Huang, HW
;
Hsueh, TH
We report a novel method of fabricating gallium nitride (GaN) nanotods of controllable dimension and density from GaN epitaxial film using inductively coupled plasma reactive ion etching (ICP-RIE). The GaN epitaxial film was grown on a sapphire substrate by metal-organic chemical vapor deposition. Under the fixed Cl-2/Ar flow rate of 10/25 sccm and ICP/bias power of 200/200 W. the GaN nanorods and array were fabricated with a density of 10(8)-10(10) cm(-2) and dimension of 20-100 nm by varying the chamber pressure from 10 to 30 mTorr. The technique offers one-step, controllable method for the fabrication of GaN nanostructures and should be applicable for the fabrication of GaN-based nano-optoelectronic devices.
Preparation and characterization of polystyrene-clay nanocomposites by free-radical polymerization
(2002-08-15)
Tseng, CR
;
Wu, JY
;
Lee, HY
;
Chang, FC
;
應用化學系
The polymerizable cationic surfactant, vinylbenzyldimethylethanolammouium chloride (VBDEAC), was synthesized to functionalize montmorillonite (MMT) clay and used to prepare exfoliated polystyrene-clay nanocomposites. The organophilic MMT was prepared by Na(+) exchanged montmorillonite and ammonium cations of the VBDEAC in an aqueous medium. Polystyrene-clay nanocomposites were prepared by free-radical polymerization of the styrene containing intercalated organophilic MMT. Dispersion of the intercalated montmorillonite in the polystyrene matrix determined by X-ray diffraction reveals that the basal spacing is higher than 17.6 nm. These nanocomposites were characterized by differential scanning calorimetry (DSC), transmission electron micrograph (TEM), thermal gravimetric analysis (TGA), and mechanical properties. The exfoliated nanocomposites have higher thermal stability and better mechanical properties than the pure polystyrene. (C) 2002 Wiley Periodicals, Inc.
Theory of resonant states of hydrogenic impurities in quantum wells
(2002-08-15)
Yen, ST
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The binding energy and the density-of-states spectrum of resonant impurity states in quantum well structure have been theoretically studied with variation of the impurity position taken into account, using the multisubband model and the resolvent operator technique. Calculations for the 2p(0) resonant state in a GaAs-Al0.2Ga0.8As quantum well have been performed. It has been found that there can be a considerable resonant coupling in the 2p(0) state, causing a similar to0.1 ps capture or escape time of electrons between the 2p(0) localized state and the first subband states. The maximum shift of the impurity energy is in general of the order of 0.1 meV, much smaller than the maximum binding energy of the 2p(0) state.
Electrical and optical properties of beryllium-implanted Mg-doped GaN
(2002-08-15)
Yu, CC
;
Chu, CF
;
Tsai, JY
;
Lin, CF
;
Wang, SC
We investigated the electrical and optical characteristics of beryllium implanted Mg-doped GaN materials. The Mg-doped GaN samples were grown by metalorganic chemical vapor deposition system and implanted with Be ions at two different energies of 50 and 150 keV and two different doses of about 10(13) and 10(14) cm(-2). The implanted samples were subsequently rapidly thermal annealed at 900, 1000, and 1100 degreesC for various periods. The annealed samples showed an increase of hole concentration by three orders of magnitude from nonimplanted value of 5.5x10(16) to 8.1x10(19) cm(-3) as obtained by Hall measurement. The high hole concentration samples also showed low specific resistance ohmic contact of about 10(-3) Omega cm(2) and 10(-6) Omega cm(2) using Ni/Au and Ni/Pd/Au metallization, respectively, without any further annealing process. It is also found from the temperature dependent photoluminescence that the activation energy of Mg dopants of the Be implanted samples has an estimated value of about 170 meV, which is nearly 30% lower than the as-grown samples of about 250 meV. The crystal quality and surface morphology of the Be implanted samples measured by x-ray diffraction and atomic force microscopy show no obvious degradation in the crystal quality and surface morphology. (C) 2002 American Institute of Physics.
Efficient compact watt-level deep-ultraviolet laser generated from a multi-kHz Q-switched diode-pumped solid-state laser system
(2002-08-15)
Chang, LB
;
Wang, SC
;
Kung, AH
;
光電工程學系
;
Department of Photonics
Stable high-power operation in the deep ultraviolet is achieved from a multi-kHz diode-pumped multi-longitudinal-mode Q-switched Nd:YAG laser by fourth harmonic generation in an external resonant cavity and by fifth harmonic generation using sum-frequency mixing of the fourth harmonic and the residual fundamental in a beta-BBO crystal. Over 2.1 W of 266 nm radiation and 540 mW of 213 nm radiation were generated from a fundamental power of 7 W of 1064 nm light at 5 kHz. The overall conversion efficiency from IR to deep ultraviolet at 213 nm is larger than 7.5%. (C) 2002 Elsevier Science B.V. All rights reserved.
On analytic properties of the photon polarization function in a background magnetic field (vol B 522, pg 257, 2001)
(2002-08-15)
Kao, WF
;
Lin, GL
;
Tseng, HJ
;
物理研究所
;
Institute of Physics
Posting file partitioning and parallel information retrieval
(2002-08-15)
Ma, YC
;
Chen, TF
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
The rapid growth in Internet usages brings new challenges on designing a scalable information retrieval system. To reduce the response time of a query to a large database, we parallelize both CPU computation and disk access of Boolean query processing on a cluster of workstations. The key issue is to partition the inverted file such that, during parallel query processing, each workstation consults only its own locally resident data to complete its task. To achieve this goal, we treat the set of all postings referring to a document ID as an object to be allocated in the develop data placement problem. Following the partitioning by document ID principle, we develop posting file partitioning algorithms to transform a sequential information retrieval system to a parallel information retrieval system. The advantage is that a better speed-up can be achieved by deriving from the fast sequential approach the compressed posting file. The partitioning schemes are designed to balance work-load of workstations in parallel query processing without increasing the average disk access time per posting. The experiment shows that almost linear speed-up can be achieved and the performance bottleneck in previous work, which parallelize only disk access, can be removed. This work shows that, by using parallel processing technique, it is feasible to build a scalable information retrieval system. (C) 2001 Elsevier Science Inc. All rights reserved.
Synthetic approach to tangutorine.
(2002-08-18)
Ho, TL
;
應用化學系
;
Department of Applied Chemistry
Shrinkage- and refractive-index shift-corrected volume holograms for optical interconnects
(2002-08-19)
Chen, JH
;
Su, DC
;
Su, JC
;
光電工程學系
;
Department of Photonics
The Bragg mismatching condition for volume holograms occurs because of the changes in the thickness and the refractive index of holographic recording materials during the recording and reconstruction procedures. We propose an improved compensation method to physically correct these effects in the fabrications of volume holograms for optical interconnects. In order to show the validity of this method, Slavich photographic plate VRP-M is used to fabricate optical interconnects. The correction of the Bragg diffraction angle shift of about 2.10degrees, which is induced by 6.14% film shrinkage and 0.06 refractive index shift, is successfully demonstrated with the surface-normal configuration. A shrinkage- and refractive-index shift-corrected volume hologram with 23% diffraction efficiency is experimentally confirmed. The methodology proposed is applicable to other phase media when the associated film shrinkage and refractive-index shift data are experimentally determined. (C) 2002 American Institute of Physics.
Healing kinetics of interfacial voids in GaAs wafer bonding
(2002-08-19)
Wu, YCS
;
Hu, GZ
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A periodic structure of bonded GaAs wafers has been proposed for quasi-phase-matched second-harmonic generation. After bonding, voids were formed at the interface due to the natural topographical irregularities and contamination on the wafer surface. Within the voids, crystallites with diamond-shaped and dendritic geometries were found, which corresponded to the bonded regions. In this study, artificial voids were introduced at the bonded interface to study the growth kinetics of these crystallites, that is the healing kinetics of these voids. It was found that the crystallite geometries and the growth rates are controlled by the nucleation of new surface layers on the bonded planes, which was the slowest stage during the healing process. (C) 2002 American Institute of Physics.
High power Al0.3Ga0.7As/In0.2Ga0.8As enhancement-mode PHEMT for low-voltage wireless communication systems
(2002-08-29)
Chen, SH
;
Chang, L
;
Chang, EY
;
Wu, JW
;
Chang, CY
A 20 mm-wide enhancement-mode pseudomorphic high-electron-mobility transistor (E-PHEMT) has been developed. The device has high transconductance of 490 mS/mm, and high maximum drain current of 350 mA/mm due to the use of an Al(0.3)G(4.7)As/In0.2Ga0.8As-based structure for carrier confinement. At 1.9 GHz and 3.0 V, the E-PHEMT shows 34.1 dBm (128 mW/mm) output power with power-added efficiency (PAE) of 64.5%. At 2.4 V, the maximum saturated output power is 32.25 dBm and maximum PAE is 78.5%. The E-PHEMT demonstrates excellent power performance at 1.9 GHz and below 3 V.
Channel-sharing strategies in two-tier cellular PCS systems
(2002-09-01)
Lin, KJ
;
Tseng, YC
;
Sheu, JP
;
資訊工程學系
;
Department of Computer Science
A two-tier cellular network is characterized by macrocells and microcells overlapping in the service area. This overlapping property provides an advantage that traffic loads can be shared by channels of the two tiers to increase the performance of the system. In this paper, we propose two channel-sharing strategies, namely vertical channel-sharing and vertical-horizontal channel-sharing, to better utilize channels of the network. The call loss probability of new calls and call dropping probability of handoff calls are developed through analyses and simulations. The results justify the advantage of our strategies over existing strategies. (C) 2002 Elsevier Science B.V. All rights reserved.
Improved TaN barrier layer against Cu diffusion by formation of an amorphous layer using plasma treatment
(2002-09-01)
Ou, KL
;
Wu, WF
;
Chou, CP
;
Chiou, SY
;
Wu, CC
The thermal stability and electrical properties of plasma-treated TaN films have been investigated by Cu/TaN/Si systems. The properties of diffusion barrier were evaluated by sheet resistance, x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), energy-dispersive spectroscopy (EDS), Auger electron microscopy (AES), and reverse-biased junction leakage current. A new amorphous layer is found to form on the surface of TaN film after the plasma treatment, Plasma-treated TaN films show better barrier performance than untreated TaN films. The sheet resistance of Cu/TaN(10 nm)/Si increases apparently after annealing at 625 degreesC for 1 h, while the Cu/plasma-treated TaN(10 nm)/Si is fairly stable up to annealing at 750 degreesC. The resistance to copper diffusion in plasma-treated TaN film is more effective. This is attributed that an amorphous layer that forms on the surface of TaN film after the plasma treatment. The thermal stabilities of Cu/TaN/n(+)-p junction diodes are enhanced by plasma treatment. The Cu/TaN(10 nm)/n(+)-p and Cu/TaN(50 nm)/n(+)-p junction diodes result in large reverse-biased junction leakage currents after annealing at 525 and 575 degreesC, respectively. On the other hand, plasma-treated TaN diffusion barriers improve the integrity of junction diodes up to 650 degreesC. Nano crystallization and stuffing effects of plasma treatments are believed to impede Cu diffusion into the Si substrate and hence improve the barrier performance. (C) 2002 American Vacuum Society.
可同時感測光纖之應變與溫度分佈的方法
(2002-09-01)
祁甡
;
李健仲
;
蔣博文
本發明係提供一種可同時感測光纖之應變與溫度分佈的方法，其係利用纖核中含有不同溫度係數成份的光纖結合布里淵頻率漂移，達到應變與溫度分佈的同時量測。該方法係先提供一核心中係含有不同溫度係數成份之感測光纖，再取得該感測光纖之布里淵頻譜的主要兩個峰值頻率值，並利用布里淵頻率漂移值的變化量與應變及溫度之關係，求得一溫度變化量，進而推導得知應變變化量。本發明為利用感測光纖本身固有特性達到分離的方法，使得整個感測系統更加簡單、實用性更高，並可得到高解析度及良好之分離效果。
An all-IP approach for UMTS third-generation mobile networks
(2002-09-01)
Lin, YB
;
Pang, AC
;
Haung, YR
;
Chlamtac, I
;
交大名義發表
This article describes the UMTS all-IP approach for third-generation mobile systems, with emphasis on the core network architecture. Followng the introduction of the core network nodes, we elaborate on application-level registration, circuit-switched call origination, packet-switched call origination, and packet-switched call termination.
Characteristics of copper films deposited on H(2)-plasma-treated TaN substrate by chemical vapor deposition
(2002-09-01)
Lin, CL
;
Chen, PS
;
Chang, CL
;
Chen, MC
;
電子工程學系及電子研究所
This work investigates the chemical vapor deposition Cu films deposited on the TaN substrate with and without an H(2)-plasma treatment prior to Cu film deposition and the effect of postdeposition thermal annealing. The Cu films deposited on the H(2)-plasma-treated TaN substrate have a number of favorable properties over the films deposited on the TaN substrate without the plasma treatment. These include an increased (111)-preferred orientation, smoother film surface, and a larger effective deposition rate. However, the Cu films deposited on the H(2)-plasma-treated substrate have a higher electrical resistivity, presumably due to the smaller, grain size. The postdeposition thermal annealing enhanced the (111)-preferred orientation and decreased the resistivity of the as-deposited Cu films. We presume that the H(2)-plasma treatment, resulted in a dense and uniform distribution of hydrogen radicals adsorbed on the substrate surface, leading to the shortening of incubation time and the formation of Cu films with a smoother surface and enhanced (100)-preferred orientation. A combined process including H(2)-plasma substrate treatment prior to Cu film deposition and postdeposition thermal annealing at an appropriate temperature in N(2) ambient, is proposed for the advantage of low-resistivity and high (111)-oriented Cu film deposition. (C) 2002 American Vacuum Society.
Design and analysis of on-chip ESD protection circuit with very low input capacitance for high-precision analog applications
(2002-09-01)
Ker, MD
;
Chen, TY
;
Wu, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An ESD protection design is proposed to solve the ESD protection challenge to the analog pins for high-frequency or current-mode applications. By including an efficient power-rails clamp circuit into the analog I/O pin, the device dimension (W/L) of ESD clamp device connected to the I/O pad in the analog ESD protection circuit can be reduced to only 50/0.5 (mum/mum) in a 0.35-mum silicided CMOS process, but it can sustain the human-body-model (machine-model) ESD level of up to 6 kV (400 V). With such a smaller device dimension, the input capacitance of this analog ESD protection circuit can be significantly reduced to only similar to1.0 pF (including the bond pad capacitance) for high-frequency applications. A design model to find the optimized layout dimensions and spacings on the input ESD clamp devices has been also developed to keep the total input capacitance almost constant (within 1% variation), even if the analog input signal has a dynamic range of 1 V.