Browsing by Author "Chen, WK"

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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.
Advanced electrical imaging of dislocations in Mg-In-codoped GaN films
(2006-01-01)
Chen, SH
;
Hou, SP
;
Hsieh, JH
;
Chang, FC
;
Chen, WK
Conducting atomic force microscopy and scanning surface-potential microscopy have been applied to image the surfaces of Mg-In-codoped GaN films grown by low-pressure metal-organic chemical-vapor deposition. Biscyclopentadienylmagnesium (CP2Mg) and trimethylindium (TMIn) have been used as the codoping sources in the experiment. The dislocation density at the film surface reduces to the lowest level (similar to 1.0 X 10(9) cm(-2)) when the TMIn/CP2Mg flow rate ratio is about 1. The dislocation density tends to rise when the flow ratio increases, and carriers of the film accumulate near the rim of the dislocation at an accelerated speed. The work function of dislocation is also found lower than that of nondislocation areas. Such electrical unevenness may seriously influence the light emission of the component, which should not be ignored during fabrication and deserves careful attention. (c) 2006 American Vacuum Society.
An elucidation of solid incorporation of InGaN grown by metalorganic vapor phase epitaxy
(1998-06-01)
Ou, J
;
Chen, WK
;
Lin, HC
;
Pan, YC
;
Lee, MC
We carried out a systematic study on the solid incorporation of InGaN under various growth conditions using metalorganic vapor phase epitaxy (MOVPE). The solid distribution of InGaN was found to be very sensitive to the growth temperature, and the TMGa and TMIn flow rates. Experimental results indicated that at low Ga flow rates InGaN growth is essentially governed by thermodynamic factors, whereas at high growth rate the InGaN solid concentration is determined merely by the vapor composition in the gas phase. In regard to the effect of TMIn flow rates on InGaN growth, it was found that once In droplets form on the surface, the In growth efficiency correspondingly decreases significantly; accounting for the low In solid concentration in InGaN at high TMIn flow rates.
Characteristics of deep levels in As-implanted GaN films
(2002-09-02)
Lee, L
;
Lee, WC
;
Chung, HM
;
Lee, MC
;
Chen, WH
Hall, current-voltage and deep level transient spectroscopy measurements were used to characterize the electric properties of n-type GaN films implanted with As atoms. After 800 degreesC thermal annealing for 60 min, one additional deep level located at E-C-0.766 eV was found in the films. We presume this induced trap is an arsenic-related point defect, most likely antisite in nature. (C) 2002 American Institute of Physics.
Characteristics of optical properties of the interrupt growth method on InGaN/GaN MQW structures
(2000)
Lin, CF
;
Shu, CK
;
Lee, WH
;
Wen, TC
;
Chu, CF
The growth method and material properties of InGaN/GaN multiple quantum well (MQW) structures were studied in this experiment. The InGaN/GaN-MQW structure were deposited above the 2 mum-thick high quality GaN layers (with background carrier concentration was about 3.2 x 10(16) cm(-3)) on Al2O3 substrates. The interrupt growth time was 10 sec between GaN barrier layer and InGaN well growth at 690 degreesC. The stronger intensity and sharper photoluminescence (PL) spectra was observed from the interrupt growth MQW structures. The mean deviation of the PL peak position was lower than 1% by using the interrupt growth MQW structures at difference growth temperature. The PL spectra was become broaden and weaker by reducing the interrupt time during InGaN/GaN growth. The thickness of one pair InGaN/GaN was also identified by DCX-ray measurement and the growth rate InGaN layer was also calculated in this experiment.
Characteristics of p-type GaN films doped with isoelectronic indium atoms
(2002-12-01)
Chang, FC
;
Shen, KC
;
Chung, HM
;
Lee, MC
;
Chen, WH
The method of isoelectronic doping, is employed to prepare p-type GaN films using metalorganic chemical vapor deposition. With the addition of In atoms, the film surface becomes much smoother, and the corresponding hole concentration and resistivity are also improved, to 8.7 x 10(17) cm(-3) and similar to 1 Omega-cm, respectively. More interestingly, it is found that an ohmic I-V characteristic can be obtained in such types of films without any dehydrogenation treatment.
Crystalline structure changes in GaN films grown at different temperatures
(1997-05-15)
Lin, HC
;
Ou, J
;
Chen, WK
;
Chen, WH
;
Lee, MC
Thin GaN films were grown on (0001) sapphire at various temperatures between 520 and 1050 degrees C using metalorganic chemical vapor deposition (MOCVD). Optical properties and crystalline structures of the films were investigated by means of photoluminescence, Raman scattering, and X-ray diffraction. A noticeable structure transition occurred at around 750 degrees C with higher growth temperatures favoring the hexagonal structure and lower ones the cubic. Defect formation was also seen to be temperature dependent. The yellow luminescence which was clearly observed in our 700-850 degrees C films was attributable to the cubic and hexagonal structure mixing. The drastic reduction of yellow luminescence and the substantial enhancement of near band edge emission in the 950-1050 degrees C films indicated that this temperature range is optimum for growing high quality wurtzite films.
Date attachable electronic cash
(2000-02-15)
Fan, CI
;
Chen, WK
;
Yeh, YS
;
資訊工程學系
;
Department of Computer Science
In this paper we propose a new untraceable electronic cash scheme which makes it possible for a payer to attach the desired date to his electronic cash during a transaction. With the aid of the date attachability property, the date on which an electronic cash is deposited in the bank cannot be forged in an electronic cash scheme. It is conducive to the unforgeability of the number of days for which the cash has been stored in the bank for some necessary purposes such as interest calculation. Our scheme not only keeps the attached date from being forged but also avoids two or more different dates being attached to the same electronic cash. Furthermore, the date attachment does not affect the untraceability property of electronic cash. Comparing with typical electronic cash schemes, the extra computation required for date attachment is just hashing. (C) 2000 Elsevier Science B.V. All rights reserved.
Deep level transient spectroscopy depth profile measurements of polycrystalline zinc oxide ceramic
(1996-09-15)
Lee, WI
;
Young, RL
;
Chen, WK
;
交大名義發表
;
友訊交大聯合研發中心
A method is proposed for performing deep level transient spectroscopy depth profile measurements of defects in polycrystalline ZnO. A multilayer-chip ZnO varistor structure is adopted to minimize the number of grains connected in series. It is verified that the distributions of some defects near the ZnO grain boundary are highly nonuniform. Valuable information has been obtained from the measured defect distribution profiles.
Deep level transient spectroscopy depth profile measurements of polycrystalline zinc oxide ceramic
(1996-09-15)
Lee, WI
;
Young, RL
;
Chen, WK
;
電子物理學系
;
Department of Electrophysics
A method is proposed for performing deep level transient spectroscopy depth profile measurements of defects in polycrystalline ZnO. A multilayer-chip ZnO varistor structure is adopted to minimize the number of grains connected in series. It is verified that the distributions of some defects near the ZnO grain boundary are highly nonuniform. Valuable information has been obtained from the measured defect distribution profiles.
Dependence of deep level concentrations on ammonia flow rate in n-type GaN films
(2002-08-01)
Lee, L
;
Chang, FC
;
Chung, HM
;
Lee, MC
;
Chen, WH
Deep level transient spectroscoppy was used to characterize the deep levels of GaN films grown with various V/III ratios using metalorganic vapor phase epitaxy. Two prominent defects, located at E(C)-0.569 +/- 0.003 and E(C)-1.013 +/- 0.091 eV, were detected in this study. When the NH(3) flow rate was increased, we observed a slight increase in trap concentration of the E(C)-0.569 eV defect and a significant increase at E(C)-1.013 eV. Although a high V/III seems necessary for obtaining good quality GaN film, our results indicate that, if the ammonia is in excessive supply, it may generate a large number of E(C)-1.013 eV deep level defects, which deteriorate the film quality - which should be avoided with special care.
Effects in carrier dynamics of Isolectronic In doped in GaN films grown by metalorganic vapor phase epitaxy
(2000)
Huang, HY
;
Shu, CK
;
Lin, WC
;
Liao, KC
;
Chuang, CH
Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of donor-bound-exciton transition of pure GaN exhibits strong dependence on temperature. When In is doped into GaN, the recombination lifetime decreases sharply from 68 ps to 30 ps, irregardless of measured temperature and In doping concentration. The cause for this appearance is not clear at present. It might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process.
Effects of growth temperature on solid incorporation of AlAs1-xSbx using tertiarybutylarsine as arsenic source precursor
(1996-10-01)
Chen, WK
;
Ou, JH
;
Hsu, CH
;
交大名義發表
;
電子物理學系
We have investigated the effects of growth temperature on the solid incorporation of AlAsSb epilayers grown LJ metalorganic vapor-phase epitaxy using TMAl, TBAs and TMSb as source precursors. The solid incorporation of AlAsSb was found to be strongly affected by the pyrolysis reactions and kinetics of the source precursors, in particular, TMAl and TBAs. Our experimental results indicated that the, Al incorporation efficiency increases with the growth temperature and saturates at temperatures above similar to 625 degrees C. On the other hand, the growth behavior of As is anomalous: the As incorporation efficiency increases initially with growth temperature, and decreases monotonously at temperatures above similar to 550 degrees C. The reduced As incorporation efficiency at high temperatures may be closely related to the beta-elimination process of TBAs, and to the formation of adducts in the gas phase.
Effects of growth temperature on solid incorporation of AlAs1-xSbx using tertiarybutylarsine as arsenic source precursor
(1996-10-01)
Chen, WK
;
Ou, JH
;
Hsu, CH
;
電子物理學系
;
Department of Electrophysics
We have investigated the effects of growth temperature on the solid incorporation of AlAsSb epilayers grown LJ metalorganic vapor-phase epitaxy using TMAl, TBAs and TMSb as source precursors. The solid incorporation of AlAsSb was found to be strongly affected by the pyrolysis reactions and kinetics of the source precursors, in particular, TMAl and TBAs. Our experimental results indicated that the, Al incorporation efficiency increases with the growth temperature and saturates at temperatures above similar to 625 degrees C. On the other hand, the growth behavior of As is anomalous: the As incorporation efficiency increases initially with growth temperature, and decreases monotonously at temperatures above similar to 550 degrees C. The reduced As incorporation efficiency at high temperatures may be closely related to the beta-elimination process of TBAs, and to the formation of adducts in the gas phase.
Effects of thermal annealing on Ni/Ta/n-GaN Schottky diodes
(2001-03-15)
Chen, GL
;
Chang, FC
;
Chung, WC
;
Huang, BR
;
Chen, WH
The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800 degreesC. Preliminary results indicate that when a Th intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.
Electrical properties of the free-standing diamond film at high voltages
(2001-05-01)
Huang, BR
;
Ke, WC
;
Chen, WK
;
電子物理學系
;
Department of Electrophysics
Polycrystalline diamond films were deposited on P-type (100) silicon substrates by the microwave plasma chemical vapor deposition system. The free-standing diamond film was then obtained by etching the silicon substrate with a KOH I solution. It was found that more non-diamond components, i.e., SiC and amorphous carbon, existed on the bottom surface of the free-standing diamond film. Two different contact geometries, coplanar contact and sandwich contact geometries, were used to characterize the in-plane and transverse hi.-h-voltage electrical properties of the free-standing diamond film, respectively. The transverse electrical property of the free-standing diamond film showed the asymmetric current-voltage (1-V) characteristic and lower break-down voltage at -220 V and 850 V. However, the in-plane electrical property exhibited the symmetric I-V characteristic in the range of - 1100 V to 1100 V. The electrical properties were successfully represented by the Frenkel-Poole conduction mechanism at high voltages (> 200 V). The simulated results indicated that the breakdown field was strongly related to the Coulombic center density of the free-standing diamond film.
Formation of self-assembled ZnTe quantum dots on ZnSe buffer layer grown on GaAs substrate by molecular beam epitaxy
(2002-07-01)
Kuo, MC
;
Yang, CS
;
Tseng, PY
;
Lee, J
;
Shen, JL
Self-assembled ZnTe quantum dot structures were grown by molecular beam epitaxy on GaAs substrates with a 200 nm ZnSe buffer layer. Surface morphology was studied by atomic force microscopy. A three-dimensional Volmer-Weber growth mode was identified. Two types of dots were observed. Strong photoluminescence observed at 1.9-2.2 eV was attributed to emission from the large type II ZnTe quantum dots. Emission from the smaller ZnTe quantum dots was observed at an energy of around 2.26 eV. The density of the larger and smaller dots was approximately 10(8)/cm(2) and 10(9)/cm(2), respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
Formation of self-organized GaN dots on Al0.11Ga0.89N by alternating supply of source precursors
(2004-06-15)
Ke, WC
;
Huang, HY
;
Ku, CS
;
Yen, KH
;
Lee, L
The self-organized GaN dot structure is successfully grown on a slightly lattice-mismatched Al0.11Ga0.89N epilayer using flow-rate modulation epitaxy (FME) growth technique. From the variation of dot density with growth temperature, we can observe that the GaN dot growth is controlled predominately by the surface diffusion of Ga adatoms at substrate temperatures below 915degreesC and by re-evaporation at higher temperatures. Because of the special alternating gas supply feature in FME, during the Ga source step, it is the Ga metal that is deposited on the underlying Al0.11Ga0.89N layer. This is because of the large lattice mismatch of 41.8% between the Ga metal (4.51 Angstrom) and Al0.11Ga0.89N (3.18 Angstrom). We consider that the GaN dot growth in our study is mainly through the Volmer-Weber growth mode, not the commonly used Stranski-Krastanow growth mode.
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.