Browsing by Issue Date, starting with "1996-06-10"

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High quality Al(Ga)As/GaAs/Al(Ga)As quantum wells grown on (111)A GaAs substrates
(1996-06-10)
Chin, A
;
Lee, K
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
We report the growth of high quality molecular beam epitaxy (MBE) AlGaAs, AlGaAs/GaAs/ AlGaAs, and AlAs/GaAs/AlAs multiple quantum wells (MQWs) on (111)A GaAs substrates. For (111)A AlGaAs/GaAs/AlGaAs MQWs, there is no detectable photoluminescence (PL) at a growth temperature of 640 degrees C, and narrow PL linewidth can only be obtained at growth temperatures higher than 680 degrees C. A PL linewidth of 13.8 meV is measured at the growth temperature of 720 degrees C. To understand such growth temperature dependence of (111)A MQWs, we have investigated the material quality of (111)A AlGaAs at different growth temperatures. The strong PL integrated intensity of 640 degrees C grown (111)A AlGaAs indicates good material quality and a low concentration of non-radiative recombination centers. However, the broad PL linewidth of 640 degrees C grown (111)A AlGaAs indicates the strong compositional modulation and a rough growth front. We have used AlAs instead of AlGaAs in order to reduce the compositional modulation and smooth the interface. A PL linewidth of 13.4 meV is measured for 640 degrees C grown (111)A AlAs/GaAs/AlAs MQWs, which is the narrowest value for (111)A MQWs. (C) 1996 American Institute of Physics.
X-ray crystallographic study of GaN epitaxial films on Al2O3(0001) substrates with GaN buffer layers
(1996-06-10)
Lee, CH
;
Chi, GC
;
Lin, CF
;
Feng, MS
;
Guo, JD
Samples of GnN(0001) epitaxial films on sapphire Al2O3(0001) with different thicknesses of GaN buffer layers were characterized by x-ray diffraction method in both in-plane and plane-normal directions. The results show that all the epitaxial films Me of good quality with the GaN[<10(1)over bar 0>] parallel to Al2O3[<11(2)over bar 0>] and GaN[<1(2)over bar 10>]parallel to Al2O3[<1(1)over bar 00>]. This arrangement of crystal orientation can be attributed to the chemical potential overriding the lattice spacing mismatch. The x-my results also indicate that the crystal coherence lengths; in the in-plane direction are smaller than those measured in the plane-normal direction, i.e., a columnar-like structure normal to the film is observed; The rocking curve widths in the in-plane direction are also larger than those measured in the plane-normal direction. In-plane measurement of rocking curve and coherence length are essential physical quantities directly related to the electron mobility which was measured predominantly in the in-plane direction. The best epitaxial structure is the one grown with 10 nm buffer layer. (C) 1996 American Institute of Physics.
High quality Al(Ga)As/GaAs/Al(Ga)As quantum wells grown on (111)A GaAs substrates
(1996-06-10)
Chin, A
;
Lee, K
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We report the growth of high quality molecular beam epitaxy (MBE) AlGaAs, AlGaAs/GaAs/ AlGaAs, and AlAs/GaAs/AlAs multiple quantum wells (MQWs) on (111)A GaAs substrates. For (111)A AlGaAs/GaAs/AlGaAs MQWs, there is no detectable photoluminescence (PL) at a growth temperature of 640 degrees C, and narrow PL linewidth can only be obtained at growth temperatures higher than 680 degrees C. A PL linewidth of 13.8 meV is measured at the growth temperature of 720 degrees C. To understand such growth temperature dependence of (111)A MQWs, we have investigated the material quality of (111)A AlGaAs at different growth temperatures. The strong PL integrated intensity of 640 degrees C grown (111)A AlGaAs indicates good material quality and a low concentration of non-radiative recombination centers. However, the broad PL linewidth of 640 degrees C grown (111)A AlGaAs indicates the strong compositional modulation and a rough growth front. We have used AlAs instead of AlGaAs in order to reduce the compositional modulation and smooth the interface. A PL linewidth of 13.4 meV is measured for 640 degrees C grown (111)A AlAs/GaAs/AlAs MQWs, which is the narrowest value for (111)A MQWs. (C) 1996 American Institute of Physics.
AuGePt ohmic contact to n-type InP
(1996-06-15)
Huang, WC
;
Lee, CL
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work studied the AuGe to n-InP/ohmic contact system with the addition of Pt. It studied two contact schemes, i.e., Au/Ge/Pt/n-InP and Au/Pt/Au/Ge/n-InP. The specific contact resistances, the thermal stability, as well as the microstructure of the system, were systematically studied with the aid of scanning electron microscopy, Auger electron spectroscopy, Rutherford backscattering analysis, and x-ray diffraction. The processing condition to achieve the optimum contact resistance was also sought and it was found that a specific contact resistance of 2.15x10(-6) Ohm cm(2) could be obtained if the Au/Ge/Pt/n-InP contact system was rapid thermal annealed at 550 degrees C for 30 s. The system was also found to be able to achieve low specific contact resistances for a wide range of anneal temperature from 400 to 550 degrees C. It was found that the Pt existence in-between AuGe and InP improved the surface morphology, the contact interface uniformity, and the thermal stability. The system could withstand a thermal aging at 400 degrees C for 80 h with only a minimal increase on the specific contact resistance. (C) 1996 American Institute of Physics.
AuGePt ohmic contact to n-type InP
(1996-06-15)
Huang, WC
;
Lee, CL
;
電子工程學系及電子研究所
;
電控工程研究所
;
Department of Electronics Engineering and Institute of Electronics
This work studied the AuGe to n-InP/ohmic contact system with the addition of Pt. It studied two contact schemes, i.e., Au/Ge/Pt/n-InP and Au/Pt/Au/Ge/n-InP. The specific contact resistances, the thermal stability, as well as the microstructure of the system, were systematically studied with the aid of scanning electron microscopy, Auger electron spectroscopy, Rutherford backscattering analysis, and x-ray diffraction. The processing condition to achieve the optimum contact resistance was also sought and it was found that a specific contact resistance of 2.15x10(-6) Ohm cm(2) could be obtained if the Au/Ge/Pt/n-InP contact system was rapid thermal annealed at 550 degrees C for 30 s. The system was also found to be able to achieve low specific contact resistances for a wide range of anneal temperature from 400 to 550 degrees C. It was found that the Pt existence in-between AuGe and InP improved the surface morphology, the contact interface uniformity, and the thermal stability. The system could withstand a thermal aging at 400 degrees C for 80 h with only a minimal increase on the specific contact resistance. (C) 1996 American Institute of Physics.
Studies of grain size effects in rf sputtered CdS thin films
(1996-06-15)
Tsai, CT
;
Chuu, DS
;
Chen, GL
;
Yang, SL
;
電子物理學系
CdS thin films with various grain sizes were produced by rf sputtering and in situ postannealing processes. For a series of annealing time intervals, the average grain sizes of an as-deposited thin film with thickness similar to 4000 Angstrom were found to vary from similar to 280 to similar to 1500 Angstrom. Three bands located in the green, yellow, and red regions were observed in photoluminescence (PL) spectra of these as-deposited films. The temperature dependence of (PL) spectra of CdS microcrystals was investigated. The variations of the (PL) spectra with average grain size and thickness of CdS thin films were also studied. It was found that the intensity of the yellow band was increased as increasing the film thickness while the intensity of the red band was decreased as the grain size of the film became larger. The peak positions of the yellow and red bands were found to be blue-shifted as the films became thinner. (C) 1996 American Institute of Physics.
Studies of grain size effects in rf sputtered CdS thin films
(1996-06-15)
Tsai, CT
;
Chuu, DS
;
Chen, GL
;
Yang, SL
;
電子物理學系
CdS thin films with various grain sizes were produced by rf sputtering and in situ postannealing processes. For a series of annealing time intervals, the average grain sizes of an as-deposited thin film with thickness similar to 4000 Angstrom were found to vary from similar to 280 to similar to 1500 Angstrom. Three bands located in the green, yellow, and red regions were observed in photoluminescence (PL) spectra of these as-deposited films. The temperature dependence of (PL) spectra of CdS microcrystals was investigated. The variations of the (PL) spectra with average grain size and thickness of CdS thin films were also studied. It was found that the intensity of the yellow band was increased as increasing the film thickness while the intensity of the red band was decreased as the grain size of the film became larger. The peak positions of the yellow and red bands were found to be blue-shifted as the films became thinner. (C) 1996 American Institute of Physics.
Collective excitations in a single-layer carbon nanotube
(1996-06-15)
Lin, MF
;
Chuu, DS
;
Huang, CS
;
Lin, YK
;
Shung, KWK
The inter-pi-band response function of a single-layer carbon nanotube is calculated within the random-phase approximation. Such a cylindrical system exhibits rich inter-pi-band excitations. The decoupled pi plasmons;of different angular momenta (L's) strongly depend on the transferred momenta (q's). Furthermore, they exhibit a dimensionality crossover as the nanotube radius is increased. For small q's and L's, the pi plasmon frequency is similar to 6-8 eV, which is insensitive to the nanotube geometry such as the radius and chiral angle. Comparison with recent experiments is discussed.
A four channel polarization and wavelength separation element using substrate-mode stacked holograms
(1996-06-17)
Chang, JT
;
Su, DC
;
Huang, YT
;
電子工程學系及電子研究所
;
光電工程研究所
A four channel polarization and wavelength separation element using substrate-mode stacked holograms is proposed based on the diffraction efficiency characteristics for polarization and the wavelength selectivity of a transmission-type phase volume grating. We fabricated a sample device and measured its polarization selectivity, output spectrum, and insertion loss of each channel to demonstrate its performance. (C) 1996 American Institute of Physics.
A four channel polarization and wavelength separation element using substrate-mode stacked holograms
(1996-06-17)
Chang, JT
;
Su, DC
;
Huang, YT
;
電子工程學系及電子研究所
;
光電工程學系
A four channel polarization and wavelength separation element using substrate-mode stacked holograms is proposed based on the diffraction efficiency characteristics for polarization and the wavelength selectivity of a transmission-type phase volume grating. We fabricated a sample device and measured its polarization selectivity, output spectrum, and insertion loss of each channel to demonstrate its performance. (C) 1996 American Institute of Physics.
Estimates of loss probabilities for delay-sensitive traffic in ATM networks
(1996-06-20)
Lai, KC
;
Lee, TH
;
傳播研究所
;
電控工程研究所
;
Institute of Communication Studies
Simple estimates of loss probabilities for heterogeneous delay-sensitive traffic in ATM networks are presented. Cells of different connections can have different loss priorities. Numerical results show that the estimates, which are derived from the bufferless fluid flow model, are close to the actual cell loss probabilities.
Measurements and modeling of radio propagation in large offices with low metallic partitions
(1996-06-20)
Ju, KM
;
Tarng, JH
;
電信工程研究所
;
Institute of Communications Engineering
A theoretical model is developed to predict the propagation loss of UHF radio waves in large modem offices with low metallic partitions. It is found that in addition to free-space propagation loss the shadowing loss due to the blockage by the low partitions in the out-of-sight situation becomes the dominant one. The shadowing loss can be efficiently formulated by using the theory of single or double knife-edge diffraction. The model has been verified by an experiment conducted at 905 MHz, 1.75 GHz, and 2.44 GHz in large offices. The model shows reasonable accuracy. (C) 1996 John Wiley & Sons, Inc.
Measurements and modeling of radio propagation in large offices with low metallic partitions
(1996-06-20)
Ju, KM
;
Tarng, JH
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
A theoretical model is developed to predict the propagation loss of UHF radio waves in large modem offices with low metallic partitions. It is found that in addition to free-space propagation loss the shadowing loss due to the blockage by the low partitions in the out-of-sight situation becomes the dominant one. The shadowing loss can be efficiently formulated by using the theory of single or double knife-edge diffraction. The model has been verified by an experiment conducted at 905 MHz, 1.75 GHz, and 2.44 GHz in large offices. The model shows reasonable accuracy. (C) 1996 John Wiley & Sons, Inc.
The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer
(1996-06-24)
Lin, CF
;
Chi, GC
;
Feng, MS
;
Guo, JD
;
Tsang, JS
The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 degrees C. The following 1.3 mu m epitaxial GaN growth was carried out at 1025 degrees C. We varied the ramping rate from 12.5 to 100 degrees C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 degrees C/min. The maximum mobility is 435 cm(2)/V s at carrier concentration of 1.7 x 10(17) cm(-3). The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 degrees C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer. (C) 1996 American Institute of Physics.
Reactive compatibilization of the poly(ethylene terephthalate) liquid crystalline polymer blends by solid epoxy resin as a coupling agent
(1996-06-27)
Chin, HC
;
Chiou, KC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A selected reactive coupling agent can be served as an effective compatibilizer for certain immiscible and incompatible blends should both blend constituents possess the necessary functional groups that can react with the coupling agent at comparable rates. Solid epoxy resin with two epoxide endgroups per molecule was demonstrated to be an efficient reactive compatibilizer for the incompatible blends of poly(ethylene terephthalate) (PET) and co-polyester liquid crystalline polymer (LCP) by functioning as a coupling agent. The main chain structure of the epoxy resin is neither identical nor miscible with PET and LCP and tends to reside at interface during melt mixing. This preferential residence gives the epoxy compatibilizer greater opportunity to react with both PET and LCP simultaneously to produce the in situ-formed epoxy-b-PET-b-LCP mixed copolymer. This in situ-formed mixed copolymer is highly effective in compatibilizing the PET/LCP blends. This reactive epoxy compatibilizer enhances the LCP fibril formation and results in substantial improvements on stiffness and toughness of the PET/LCP blends. (C) 1996 John Wiley & Sons, Inc.
Reactive compatibilization of the poly(ethylene terephthalate) liquid crystalline polymer blends by solid epoxy resin as a coupling agent
(1996-06-27)
Chin, HC
;
Chiou, KC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A selected reactive coupling agent can be served as an effective compatibilizer for certain immiscible and incompatible blends should both blend constituents possess the necessary functional groups that can react with the coupling agent at comparable rates. Solid epoxy resin with two epoxide endgroups per molecule was demonstrated to be an efficient reactive compatibilizer for the incompatible blends of poly(ethylene terephthalate) (PET) and co-polyester liquid crystalline polymer (LCP) by functioning as a coupling agent. The main chain structure of the epoxy resin is neither identical nor miscible with PET and LCP and tends to reside at interface during melt mixing. This preferential residence gives the epoxy compatibilizer greater opportunity to react with both PET and LCP simultaneously to produce the in situ-formed epoxy-b-PET-b-LCP mixed copolymer. This in situ-formed mixed copolymer is highly effective in compatibilizing the PET/LCP blends. This reactive epoxy compatibilizer enhances the LCP fibril formation and results in substantial improvements on stiffness and toughness of the PET/LCP blends. (C) 1996 John Wiley & Sons, Inc.
Like sign top quark pair production at linear colliders
(1996-06-27)
Hou, WS
;
Lin, GL
;
物理研究所
;
Institute of Physics
In the general two Higgs doublet model with flavor changing neutral Higgs couplings, neutral Higgs bosons may decay dominantly via or <(t)over bar c> final states. At the linear collider, e(+)e(-) --> h(0)A(0) or H(0)A(0) production processes may result in , W+W- t (c) over bar or tt (c) over bar (c) over bar (or (t) over bar (t) over bar cc) final states. The process yy --> h(0), A(0) --> t (c) over bar is also promising, but e(+)e(-) --> (h(0), H-0)Z(0) --> is relatively suppressed. The possibility of observing like sign lepton pairs, usually the hallmark for neutral meson mixing, is quite interesting since T-0 mesons do not even form.
An innovation approach to optimize a Kalman filter with an H-infinity error bound by secant method
(1996-07-01)
Wu, BF
;
Hsu, HH
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
Designing a Kalman filter with a constraint on the H-infinity norm of the estimation error was first developed by Bernstein and Haddad in 1989. The main result is a sufficient condition for characterizing the Kalman filter. In this paper, similar to the standard Kalman filter, the properties of orthogonal principles are also shown to be preserved. Furthermore, the uniqueness, as opposed to an H-infinity filter, of the filter is implied by the orthogonal principles. An innovative approach to obtaining the minimum energy with a constraint on the H-infinity norm of the estimation en ol is proposed since the original work of Bernstein and Haddad does not, in general, reach the minimum energy of the estimation error. By means of the Secant method, the energy of the estimation error can be reduced as much as possible, under the condition that the H-infinity error bound is still satisfied.
An improved dynamic model in integral equation methods for the characterization of discontinuities in planar circuits
(1996-07-01)
Sheen, JW
;
Lin, YD
;
電信工程研究所
;
Institute of Communications Engineering
An efficient method to improve the integral equations method is presented in this article. A delta gap source generator and the fundamental mode sampling technique are employed. By employing this modified method, observation of the SWR and the creation of a large matrix in the conventional method employing a delta gap source generator are not necessary. Also, the modeling complexity and the time-consuming computation of the conventional method, which employs the semiinfinite traveling-wave mode, are avoided. In this article we use the coplanar waveguide short-end discontinuity as an example to describe this method in the spectral domain. Moreover, numerical results are compared with our experimental data and they show good agreement. (C) 1996 John Wiley & Sons, Inc.
RWM-cut for color image quantization
(1996-07-01)
Yang, CY
;
Lin, JC
;
資訊工程學系
;
Department of Computer Science
A new simple method for constructing a color palette that uses the radius weighted mean cut (RWM-cut) is proposed. The method is a hierarchically divisive method, and each two-class partition uses the centroid and the RWM only. Experiments show that the RWM-cut algorithm is feasible and visually acceptable. The algorithm can either be used alone or be used to create a good initial palette for the LBG algorithm. Besides the 3-D version, a 1-D version of the RWM-cut algorithm is also included in the paper for realtime color quantization. The quantization error is small and the processing speed is competitive. Dithered images are also provided. Copyright (C) 1996 Elsevier Science Ltd