Browsing by Author "Lee, MC"

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A high-temperature thermodynamic model for metalorganic vapor phase epitaxial growth of InGaN
(1999-09-01)
Ou, J
;
Pan, YC
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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.
An elucidation of solid incorporation of InGaN grown by metalorganic vapor phase epitaxy
(1998-06-01)
Ou, J
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Chen, WK
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Lin, HC
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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
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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 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.
Comparative study of Schottky diode characteristics in Ni, Ta and Ni/Ta metal contact schemes on n-GaN
(2001-07-01)
Chen, GL
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Chang, FC
;
Chuang, WC
;
Chung, HM
;
Shen, KC
We have reported current-voltage characteristics of Ta/- and Ni/Ta/n-GaN Schottky diodes under various thermal treatments. Experimental data indicate that the electrical characteristics of Ni/Ta diodes are controlled by the interfacial properties of the Ta and GaN heterointerface for the as-deposited samples and strongly affected by the presence of an oxide layer (Ta2O5) in those high-temperature-annealed diodes. In regard to Ta/Ni diodes, probably because of thermal stability and wide-bandgap properties of tantalum oxide, dramatic improvement in Schottky diode performance was resulted after annealing at high temperatures. The corresponding barrier height and ideality factor values can reach 1.17 cV and 1.09, respectively, even at an annealing temperature of 800 degreesC.
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.
Cw mode-locked deep UV pulses at an average power of 1.8 W
(2000-11-01)
Garcia, JC
;
Newman, AK
;
Liu, JM
;
Lee, MC
;
電子物理學系
We report a cw mode-locked train of similar to3.6 ps deep UV pulses with an average power of up to 1.8 W at 263 nm. This UV source is the result of two-stage, single-pass fourth-harmonic generation of an additive-pulse mode-locked Nd:YLF laser using KTP and BBO crystals. Conversion efficiencies of up to 47% from 1.053 mum to 527 nm and up to 39% from 527 to 263 nm have been observed.
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
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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 thermal annealing on Ni/Ta/n-GaN Schottky diodes
(2001-03-15)
Chen, GL
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Chang, FC
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Chung, WC
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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.
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
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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
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Huang, HY
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Ku, CS
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Yen, KH
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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
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Wang, SF
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Lee, WH
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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
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Wang, SF
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Lee, WH
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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 X-ray characterization of an InN film on sapphire prepared by metalorganic vapor phase epitaxy
(1997-12-15)
Chen, WK
;
Pan, YC
;
Lin, HC
;
Ou, J
;
Chen, WH
We report the successful growth of an InN film by metalorganic vapor phase epitaxy. The film quality is found to be strongly dependent on the growth temperature and the TMIn reactant flow rate. The best quality epilayer was obtained at 375 degrees C under a high V/III ratio growth environment. It exhibits a FWHM of the X-ray rocking curve as narrow as 96 arcsec: which explains the superior crystalline quality of our epitaxial film.
Growth and X-ray characterization of an InN film on sapphire prepared by metalorganic vapor phase epitaxy
(1997-12-15)
Chen, WK
;
Pan, YC
;
Lin, HC
;
Ou, J
;
Chen, WH
We report the successful growth of an InN film by metalorganic vapor phase epitaxy. The film quality is found to be strongly dependent on the growth temperature and the TMIn reactant flow rate. The best quality epilayer was obtained at 375 degrees C under a high V/III ratio growth environment. It exhibits a FWHM of the X-ray rocking curve as narrow as 96 arcsec: which explains the superior crystalline quality of our epitaxial film.
Growth mode transfer of self-assembled CdSe quantum dots grown by molecular beam epitaxy
(2006-01-15)
Lai, YJ
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Lin, YC
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Fu, CP
;
Yang, CS
;
Chia, CH
Self-assembled CdSe/ZnSe quantum dots (QDs) were grown at various growth temperatures on GaAs (0 0 1) by molecular beam epitaxy. An optimum growth temperature for CdSe/ZnSe QDs was found to be 260 degrees C. The Stranski-Krastanow (SK) growth mode was confirmed clearly by atomic force microscopy images. The coherent SK QDs were observed from 2.5 monolayers (MLs). Two types of QDs were found with the CdSe coverage of 3.0 MLs. It was attributed to a growth mode change from the coherent SK growth mode to the ripening growth mode. A schematic diagram of the growth mechanism of self-assembled CdSe QDs was presented. Moreover, the photoluminescence spectra of samples with various thicknesses were investigated. A dramatic change of optical properties confirmed that the QD structure formed with thickness above 2.5 MLs. Finally, the dot size and the density distributions were controlled after growth by in-chamber thermal annealing. For the sample grown at 3.0 MLs, the distribution of dot sizes was controlled from 6.0 to 6.5 x 10(3) nm(3) at an annealing temperature of 400 degrees C. (c) 2005 Published by Elsevier B.V.
Growth temperature reduction for isoelectronic As-doped GaN
(2003-03-01)
Lee, WH
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Huang, HY
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Chen, WC
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Lee, CF
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Chen, WK
As-doped GaN films were grown at different temperatures by atmospheric metalorganic chemical vapor deposition. A higher electron Hall mobility, narrower line width in photoluminescence, and longer spatial correlation length of the filmes were obtainable at low growth temperatures compared to undoped GaN grown at the same temperatures as a result of isoelectronic As-doping.
Highly reliable nickel silicide formation with a Zr capping layer
(2003-05-01)
Lee, TL
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Lee, JW
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Lee, MC
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Lei, TF
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Lee, CL
Zr is proposed to be the capping layer for nickel silicide to obtain a stable low resistance contact system even at an annealing temperature as high as 850degreesC. A NiSi monolayer is the only phase observed in those samples annealed from 500 to 850degreesC. Experimental results from transmission electron microscopy and X-ray diffractometry analysis show that the agglomeration and precipitate of nickel silicide problems which are usually encountered in the NiSi system are eliminated. (C) 2003 The Electrochemical Society.
Influence of sapphire nitridation on properties of indium nitride prepared by metalorganic vapor phase epitaxy
(1999-02-01)
Pan, YC
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Lee, WH
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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.