Browsing by Author "Chang, CS"

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A novel 3.5-GHz microwave counter using an opto-electronic harmonic heterodyne technique
(1997-07-01)
Chang, CS
;
Chiu, HF
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
A novel 3.5-GHz microwave counter using an opto-electronic harmonic heterodyne technique has been demonstrated, The system's performance has been discussed and evaluated, and is viewed as good, in comparison with today's microwave-counting systems, It is believed that this novel device has potential for measuring signals above 100 GHz.
Cation substitution effects on structural, electronic and optical properties of nonlinear optical AgGa(SxSe1-x)(2) crystals
(2003-09-10)
Tang, LC
;
Lee, MH
;
Yang, CH
;
Huang, JY
;
Chang, CS
The structural, electronic and optical properties of tetragonal nonlinear optical (NLO) crystals, AgGa(SxSe1-x)(2) (x = 0.0, 0.25, 0.5, 0.75, and 1.0), were investigated theoretically and experimentally. The results obtained indicated that the electronic bandgaps, optical properties and bulk moduli of these compounds were linearly dependent on the substitution concentration of cations. From partial density of state analysis, it was found that the electronic states near the band edges of AgGa(SxSe1-x)(2) were a simple proportional mixture of the atomic orbitals of sulfur and selenium. A cell-volume effect was proposed as the major cause of the linear dependence of material properties on the substitution concentration. It was calculated that the second-order NLO susceptibilities were scaled with the cubic power of bandgap, although a minor deviation existed. This deviation arose from the optical transition moment products.
Design a linear motor absorber
(2006-04-15)
Chang, CS
;
Liu, TS
;
Lin, SK
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機械工程學系
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電控工程研究所
This paper raises a valid method to design a linear motor which serves as active dynamic vibration absorber to reduce disk drives vibration at multiple speeds. A better linear motor performance, such as lower consumption energy and higher electrical efficiency, can be achieved by tuning the diameter of a winding coil, the thickness of the magnet, and the winding spaces in a linear motor absorber. (C) 2006 American Institute of Physics.
Design of adaptive dynamic absorber to reduce optical disk drive vibration at multiple rotating speeds
(2006-02-01)
Chang, CS
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
In this study, we design a dynamic absorber to reduce optical disk drive vibration at multiple rotating speeds using an enlarged bandwidth control at targeted rotating speeds. In addition to the basic absorber as a passive device, a voice coil motor serves to actively control vibration. Combining passive and active devices leads to far greater stability and robustness. The proposed dynamic absorber has been validated in simulations and experiments.
Design of optical head with holographic optical element for small form factor drive systems
(2005-02-01)
Shih, HF
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Chang, CL
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Lee, KJ
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Chang, CS
;
機械工程學系
An optical head composed of an optical module and a biaxial actuator is designed for small form factor drives. This system adopts a finite-conjugate objective lens with numerical aperture 0.65 for 654-nm wavelength. A holographic optical element is used for simplifying the optical configuration which provides a better approach for alignment. The actuator is of a spider-like suspension for the focusing and is of a swing arm for the tracking.
Difference-frequency mixing of output waves from a periodically poled lithium niobate optical parametric oscillator in a GaSe crystal
(2002-08-01)
Haidar, S
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Hsu, YK
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Chang, CS
;
Wang, SC
;
Ito, H
We report on an optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) pumped by a Nd:YAG laser, and on extending its tuning range by difference-frequency mixing of OPO output waves in GaSe crystal. Maximum combined signal and idler pulse energy of 2.7 mJ and slope efficiency of 25% have been achieved. The tuning range is 1.71 to 1.98 mum for the signal wave and 2.81 to 2.30 mum for the idler wave, using a single set of mirrors. As an application of this PPLN OPO, the signal and the idler waves are difference-frequency-mixed in a GaSe crystal to produce tunable mid-IR from 4.35 to 14.25 mum. The efficiency of the mixing has been analyzed, considering the experimental results. (C) 2002 Society of Photo-optical Instrumentation Engineers.
Dynamic analog testing via ATE digital test channels
(2004)
Su, CC
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Chang, CS
;
Huang, HW
;
Tu, DS
;
Lee, CL
A dynamic analog test methodology using digital tester is proposed. A simple triangular waveform is built on the device interface board for the stimulus generation. The response waveform is quantized by the dual comparators in a digital pin electronic circuit. Statistical analysis is conducted to enhance the quantization resolution and minimize the noise effect. The experimental results using an ATE show that the error is less than 2%. It confirms the feasibility of the proposed methodology.
Effect of annealing on the structural and optical properties of AgGaS2 thin films prepared by pulsed laser deposition
(2002-11-01)
Hsu, HC
;
Chen, HH
;
Kuo, SY
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Chang, CS
;
Hsieh, WF
The influence of annealing on the AgGaS2 films groom by pulsed laser deposition has been investigated. The X-ray diffraction results show the AgGaS2 films were found with preferential orientation (1 1 2) normal to the surface and silver droplets,were diminished after the post-annealing. Photoluminescence (PL) measurements reveled the exciton energy is slightly red shifted that is possibly due to the thermal strain effect. The binding energy of the shallow, donors is similar to28 meV determined from temperature dependent PL spectra, In addition, the A-exciton and the B/C-exciton could be observed in the transmittance spectra at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
Effect of rapid thermal annealing on carrier lifetimes of arsenic-ion-implanted GaAs
(1996-08-12)
Lin, GR
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Chen, WC
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Ganikhanov, F
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Chang, CS
;
Pan, CL
Femtosecond time-resolved reflectivity measurements, structural, and electrical analyses have been performed to investigate the effect of rapid thermal annealing (RTA) on GaAs implanted with 200 keV arsenic ions at 10(16) ions/cm(2). Ultrashort carrier lifetimes from 0.48 fs to 2.3 ps were observed for samples annealed at temperatures between 600 and 800 degrees C. The time constants are somewhat shorter than those of RTA-annealed low-temperature molecular-beam epitaxy grown material, while following the same trend of longer time constants and recovery of resistance at higher annealing temperatures. Arsenic precipitates were not observed. (C) 1996 American Institute of Physics.
Effect of thermal annealing on electrical conductivities in arsenic-ion-implanted GaAs
(1996-01-29)
Chen, WC
;
Chang, CS
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
The effect of thermal annealing on the electrical conductivities of arsenic-ion-implanted GaAs has been investigated by deep level transient spectroscopy and temperature-dependent conductance measurements. For the annealed films of arsenic-ion-implanted GaAs a band of deep-level defects with the activation energy of around 0.55 eV below the conduction band is found. The dense concentration of traps is able to reduce the carrier concentration from 3 X 10(18) to 2 X 10(17) cm(-3). The cross section of the deep level is calculated to be 1.5 X 10(-14) cm(2). The carrier-transport mechanisms of both as-implanted GaAs and postannealed GaAs are dominantly shown to be a separate hopping and active-type conduction. (C) 1996 American Institute of Physics.
Electrical properties in arsenic-ion-implanted GaAs
(1996-08-01)
Chen, WC
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Chang, CS
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光電工程研究所
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Institute of EO Enginerring
A model of effective surface potential energy is proposed to explain unknown behavior of carrier transport in film and leakage currents in Schottky diodes. X-ray photoelectron spectroscopy is employed to investigate a series of band diagrams of arsenic-ion-implanted GaAs films. It is shown that the effective surface potential energies, affected by the shift of core levels, are due to different microstructures and atomic environments in these films at different annealing temperatures. Moreover, the effective barrier heights on the surfaces of these films are changed by the different effective surface potential energies which increase from 0.49 to 0.75 eV in films annealed from 200 to 600 degrees C, but slightly decrease to 0.7 eV in films annealed up to 800 degrees C. (C) 1996 American Institute of Physics.
Electrical properties in arsenic-ion-implanted GaAs
(1996-08-01)
Chen, WC
;
Chang, CS
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
A model of effective surface potential energy is proposed to explain unknown behavior of carrier transport in film and leakage currents in Schottky diodes. X-ray photoelectron spectroscopy is employed to investigate a series of band diagrams of arsenic-ion-implanted GaAs films. It is shown that the effective surface potential energies, affected by the shift of core levels, are due to different microstructures and atomic environments in these films at different annealing temperatures. Moreover, the effective barrier heights on the surfaces of these films are changed by the different effective surface potential energies which increase from 0.49 to 0.75 eV in films annealed from 200 to 600 degrees C, but slightly decrease to 0.7 eV in films annealed up to 800 degrees C. (C) 1996 American Institute of Physics.
Electrical properties of GaSe doped with Er
(2004-08-01)
Hsu, YK
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Chang, CS
;
Huang, WC
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光電工程學系
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Department of Photonics
Measurements of the Hall effect and Er-related luminescence were made on Er-doped GaSe. Deep-level transient spectroscopy (DLTS) was also performed. Hall measurements show that hole concentrations of 0.2%, 0.5%, and 1% Er-doped GaSe samples are 1.5x10(17)-6x10(17) cm(-3) at room temperature, and that the mobility of these holes is in the range 22-34 cm(2)/V s. The temperature dependence of the hole concentration is explained using the two-acceptor model, in which one acceptor level is at around 65 meV above the valence band and the other one is at similar to158 meV. The DLTS measurements yield similar results. Furthermore, the shallow acceptor impurities contribute free hole carriers and act as radiative centers; the deep acceptor impurities are nonradiative centers, which are responsible for the quenching behavior of Er-related luminescence. The temperature dependence of the hole mobility can be understood as the combined scatterings of homopolar optical phonons and ionized impurities. (C) 2004 American Institute of Physics.
Electrical properties of multiple high-dose Si implantation in p-GaN
(1999-07-15)
Lai, WC
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Yokoyama, M
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Tsai, CC
;
Chang, CS
;
Guo, JD
This work performs Si ion implantation the electrical conductive type of the p-GaN film from p-type to n-type. Multiple implantation method is also used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implant energies for the multiple implantation are 40, 100, and 200 KeV. The implant dose is 5 x 10(15) cm(-2) for each implant energy. After implantation, the samples are annealed in a N-2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 degrees C. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implantation in p-GaN. Moreover, the rectifying I-V characteristic of the p-n GaN diode is also examined.
Electrical properties of the Si implantation in Mg doped p-GaN
(1999-11-01)
Lai, WC
;
Yokoyama, M
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Tsai, CC
;
Chang, CS
;
Guo, JD
This work performs Si ion implantation to activate and convert the electrical conduction of p-GaN films from p-type to n-type. Multiple implantation method is used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implantation energies for the multiple implantation are 10, 100, and 200 keV. The implantation dose is 5 x 10(15) cm(2) for each implantation energy. After implantation, the samples were annealed in an N-2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 degrees C,. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implant in p-GaN. In addition, the rectifying I-V characteristic of the p-n GaN diode is also examined.
Electronic structure and optical properties of rhombohedral CsGeI3 crystal
(2000-10-30)
Tang, LC
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Chang, CS
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Huang, JY
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光電工程學系
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Department of Photonics
We analyse the electronic structure of the perovskite crystal CsGeI3 by means of first-principles calculations and compare our findings to experimental results. Our calculation indicates that CsGeI3 has a direct-transition gap of 0.74 eV at (k) over right arrow = (pi /a)(111). The top of the valence bands was found to mainly comprise the 5p orbitals of iodine, while the bottom of the conduction bands is dominated by the 4p orbital of germanium. Photoluminescence (PL) measurements on a single crystal of CsGeI3 indicate two peaks, one at 0.82 mum (1.51 eV) and the other at 1.15 mum (1.08 eV). The shorter-wavelength PL peak is assigned as arising from an interband transition at (k) over right arrow = (pi /a)(111) and the longer-wavelength PL is presumably ascribable as originating from a transition involving an energy level within the fundamental band gap. Fourier-transformed infrared spectroscopy reveals that the transparent range of CsGeI3 could extend from similar to2 mum to >12 mum The short-wavelength cut-off is mainly limited by the energy band gap, while the long-wavelength limit possibly originates from lattice phonon absorption. Raman spectra of the crystal exhibit two major peaks at 105 cm(-1) and 151 cm(-1) and the corresponding overtones at 220 cm(-1) and 293 cm(-1).
Excess low-frequency noise in ultrathin oxide n-MOSFETs arising from valence-band electron tunneling
(2005-09-01)
Wu, JW
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You, JW
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Ma, HC
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Cheng, CC
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Hsu, CF
Low-frequency flicker noise in analog n-MOSFETs with 15-angstrom gate oxide is investigated. A new noise generation mechanism resulting from valence-band electron tunneling is proposed. In strong inversion conditions, valence-band electron tunneling from Si substrate to polysilicon gate takes place and results in the splitting of electron and hole quasi-Fermi-levels in the channel. The excess low-frequency noise is attributed to electron and hole recombination at interface traps between the two quasi-Fermi-levels. Random telegraph signals due to the capture of channel electrons and holes is characterized in a small area device to support our model.
Fabrication and optical property of GaSe thin films grown by pulsed laser deposition
(2003-08-01)
Lee, SH
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Hsu, YK
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Hsu, HC
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Chang, CS
;
Hsieh, WF
The highly oriented (001) GaSe film on c-cut sapphire (0001) was successfully fabricated by pulsed laser deposition. As growth temperature decreases from 550degreesC to 375degreesC, the structure of films changes from cubic zinc-blende Ga2Se3 phase to GaSe phase. The growth temperature of the critical transition from Ga2Se3 phase to GaSe phase is around 500degreesC . From atomic force microscope (AFM) results, it is observed that the growth process of GaSe film is in the manner of layer plus island growth. Besides, the optimal growth conditions of as-grown GaSe film were obtained at a substrate temperature of 400degreesC and laser energy density of 11.7J/cm(2). When the thickness of films goes beyond 800 Angstrom, the stress will be released and the thickness of 1200 Angstrom results in an optimal GaSe film. Furthermore, the indirect bound exciton emission and the recombination via impurity levels or structural defects were observed from low-temperature photoluminescence measurement.
Growth of ZnO nanowires without catalyst on porous silicon
(2004-12-01)
Chang, CC
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Chang, CS
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光電工程學系
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Department of Photonics
Porous silicon (PS) technology is, for the first time, used to grow ZnO nanowires on the surface of a PS substrate with a rough morphology without any catalyst. The characteristics of these nanowires were investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), grazing-angle X-ray diffraction (XRD) and photoluminescence (PL) measurements. Zn vapor condenses easily on the PS surface and forms a wetting layer, but not on the flat Si surface. The PS surface provides a rough surface morphology to form a wetting layer by decreasing the surface energy so that ZnO nanowires can grow without any catalyst. The Zn-rich composition changed during growth; the ratio of zinc to oxygen was near to one at the top part of the nanowires. The probable growth mechanism was the vapor-solid (VS) process. In principle, the selective growth of ZnO nanowires on Si-base devices for optoelectronic application is possible.
Intelligent leaky bucket algorithms for sustainable-cell-rate usage parameter control in ATM networks
(2004-10-01)
Chang, CJ
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Yu, CH
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Chang, CS
;
Lin, LF
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電信工程研究所
In this paper, we propose two intelligent leaky bucket algorithms for sustainable-cell-rate usage parameter control of multimedia transmission in asynchronous transfer mode networks. One is the fuzzy leaky bucket algorithm, in which a fuzzy increment controller (FIC) is incorporated with the conventional leaky bucket algorithm; the other is the neural fuzzy leaky bucket algorithm, where a neural fuzzy increment controller (NFIC) is added with the conventional leaky bucket algorithm. Both the FIC and the NFIC properly choose the long-term mean cell rate and the short-term mean cell rate as input variables to intelligently determine the increment value. Simulation results show that both intelligent leaky bucket algorithms have significantly outperformed the conventional leaky bucket algorithm, by responding about 160% faster when taking control actions against a nonconforming connection while reducing as much as 50% of the queueing delay experienced by a conforming connection. In addition, the neural fuzzy leaky bucket algorithm outperforms the fuzzy leaky bucket algorithm, in aspects of three performance measures such as selectivity, responsiveness, and queueing delay, especially when the traffic flow is bursty, dynamic, and nonstationary.