Browsing by Author "Chang, H"

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A high-temperature thermodynamic model for metalorganic vapor phase epitaxial growth of InGaN
(1999-09-01)
Ou, J
;
Pan, YC
;
Lee, WH
;
Shu, CK
;
Lin, HC
A thermodynamic analysis tailored with a high-temperature parameter was performed for metalorganic vapor phase epitaxial (MOVPE) growth of InxGa1-xN alloys. Accordingly, a series of InGaN samples were prepared under various input In flow rates and growth temperatures. Theoretical results indicate that the In solid concentration tends to increase with increasing In flow rate and with decreasing temperature, whereas the metal droplets form more easily on the surface at lower growth temperatures and higher In fluxes, which are in good agreement with our experimental data.
A new CMOS readout circuit design for the IR FPA with adaptive gain control and current-mode background suppression
(1996)
Hsieh, CC
;
Wu, CY
;
Jih, FW
;
Sun, TP
;
Chang, H
Far-infrared resonance in split ping resonators
(2004-02-01)
Hsu, AC
;
Cheng, YK
;
Chen, KH
;
Chern, JL
;
Wu, SC
We experimentally investigated the resonance effect of planar metallic split ring resonators (SRRs) in the far-infrared region (FIR) (similar to10.6 mum). Experimental results indicated that they exhibit resonance around 10.6 mum, implying negative permeability in the FIR region. Furthermore, the ratio of effective dimensions of the SRR cell and the wavelength of the incident beam was around I which suggested a wide scale independence. This size tolerance is useful in realizing the meta-materials with negative indices of refraction in the optical wavelength domain.
Gallium K-edge EXAFS study of GaN : Mg films
(2000)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lin, WC
;
Shu, CK
Ga K-edge extended X-ray absorption fine structure (EXAFS) measurement was employed to investigate the local structure of GaN:Mg films grown by metalorganic vapor phase epitaxy (MOVPE) with various Cp,Mg dopant flow rates using both in-plane and out-of-plane polarization modes of X-ray. The near edge absorption spectra were found to depend on X-ray polarization strongly for undoped GaN sample and weakly to minutely for heavily Mg-doped and amorphous films. The results indicate Mg incorporation modifies the local structure around the absorber Ga atom and, hence, alters the molecular orbital electron transition of GaN sample. EXAFS analysis showed both vacancy and Mg-interstitial defects contribute to the reduction of coordination numbers along the hexagonal c-axis of GaN:Mg film.
Gallium K-edge x-ray absorption study on Mg-doped GaN
(2001-01-01)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lee, MC
;
Chen, WK
Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples. (C) 2001 American Institute of Physics.
Growth and fatigue properties of pulsed laser deposited Pb1-xLax(ZryTiz)O-3 thin films with [001] preferred orientation
(1996-12-01)
Lin, WJ
;
Tseng, TY
;
Wu, YZ
;
Lin, SP
;
Tu, SL
Growth of [00/] preferentially oriented Pb1-xLax(ZryTiz) O-3 (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 degrees C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [00/]-textured PLZT thin films. The ferroelectric and fatigue properties were examined. The films deposited on YBa2Cu3O7-x and CeO2 coated silicon (YBCO/CeO2/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO3 (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/BCO/CeO2/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10(8) polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10(8) cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P=[111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P=[001]) lies along the film's normal such that switch cycles cause no lateral stress.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Influence of sapphire nitridation on properties of indium nitride prepared by metalorganic vapor phase epitaxy
(1999-02-01)
Pan, YC
;
Lee, WH
;
Shu, CK
;
Lin, HC
;
Chiang, CI
Indium nitride films have been successfully grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) using TMIn and NH3 as source precursors. Experimental results indicated that pregrowth treatments, such as buffer layer growth, nitridation temperature and nitridation duration have dramatic effects on the growth of the InN films. For films nitridated at 1,000 degrees C for 40 min without any buffer layer growth, we obtained an InN film quality with Hall mobility, carrier concentration and line width of Raman E-2 mode of 270 cm(2)/V.s, 5 x 10(19) cm(-3) and 4.5 cm(-1), respectively, which is among the best quality ever reported for such type of film grown by MOVPE.
Long-term photocapacitance decay behavior in undoped GaN
(2000)
Chung, HM
;
Pan, YC
;
Chung, WC
;
Chen, NC
;
Tsai, CC
We have employed the photocapacitance measurement to examine the physical properties of GaN Schottky diode made from the undoped epilayer grown by metalorganic vapor phase epitaxy. The resulted transient capacitance spectrum shows that the diode exhibits a characteristic of long-term logarithmic-type decaying behavior, which, we believe, is correlated closely to the linear arranged traps close to the core of the threading edge dislocations.
Optical image recognition using photorefractive crystal plates
(1997)
Hsieh, ML
;
Lin, SH
;
Hsu, KY
;
Hsieh, TC
;
Lin, SP
We demonstrate a real-time optical image recognition system using photorefractive thin plates. The effects of donor/acceptor concentration ratio in thin lithium niobate crystal plates on the photorefractive response time and the grating diffraction efficiency are presented.
Photorefractive Fe : LiNbO3 crystal thin plates for optical information processing
(1999-07-01)
Lin, SH
;
Hsieh, ML
;
Hsu, KY
;
Hsieh, TC
;
Lin, SP
The effects of the donor acceptor concentration ratio in iron-doped Lithium niobate (Fe:LiNbO3) crystal plates on photorefractive response time and on grating diffraction efficiency are studied both theoretically and experimentally. The results provide a useful guide for designing photorefractive plates far optical information-processing applications. Two devices for real-time image recognition have been demonstrated: a photorefractive joint-transform correlator and a VanderLugt correlator. The former emphasizes fast response time, and the latter emphasizes high diffraction efficiency. By appropriate adjustment of the dopant concentration and the ratio of the donor acceptor levels, photorefractive Fe:LiNbO3 crystals that facilitate specific applications have been designed and fabricated. Shift-invariant image correlations have been achieved. (C) 1999 Optical Society of America [S0740-3224(99)01307-7].
Structure study of GaN : Mg films by X-ray absorption near-edge structure spectroscopy
(2001)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lin, WC
;
Chiang, CI
X-ray absorption near-edge fine structure (XANES) spectroscopy from N K-edge measurement was employed to examine the crystal structure of metallorganic vapor phase epitaxy (MOVPE) grown Mg-doped GaN (GaN:Mg) films. The result showed that Mg doping induced crystal stacking faults to occur at the film surface causing a fraction of hexagonal phase to transform into cubic phase. As a consequence of this, XANES spectra of the films were found to vary with the dopant concentration and to lose pure hexagonal character when examined with the incident angle theta of the X-ray beam. Spectral characteristic variation between the two phases allows us to estimate the phase composition of the samples. The trend of increasing cubic phase component in dopant concentration is consistent with the observed Normaski optical micrograph. (C) 2001 Published by Elsevier Science Ltd.