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Yellow luminescence in n-type GaN epitaxial films
(1997-09-15)
Chen, HM
;
Chen, YF
;
Lee, MC
;
Feng, MS
;
材料科學與工程學系
Photoluminescence, resonant Raman scattering, and photoconductivity measurements have been employed to study the yellow; emission in undoped n-type and a set of Se-doped GaN epitaxial films. It is best described by a transition from the conduction-band edge to a deep acceptor. Unlike the donors and accepters used in most previous studies that substitute Ga sires, Se atoms can replace N sites. With this unique fact, we identify that the origin of the yellow emission involves the nitrogen antisite. In addition, it is found that persistent photoconductivity can be observed after the yellow; band excitation, We further suggest that the nitrogen antisite exhibits a metastable behavior similar to the arsenic antisite in GaAs.
Photoluminescence studies of GaN films of different buffer layer and doping concentration
(1998-02-01)
Shen, CC
;
Shu, CK
;
Lin, HC
;
Ou, J
;
Chen, WK
Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
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.
Raman and X-ray studies of InN films grown at different temperatures by metalorganic vapor phase epitaxy
(1998-09-01)
Chen, WK
;
Lin, HC
;
Pan, YC
;
Ou, J
;
Shu, CK
We used Raman scattering and X-ray diffraction (XRD) methods to investigate the properties of InN films deposited at temperatures ranging from 325 to 600 degrees C by metalorganic vapor phase epitaxy (MOVPE). Significant line broadening, softening and intensity evolution were observed from films at growth temperatures between 375 and 450 degrees C. This can be attributed to the formation of mixed hexagonal and cubic structures and related dislocation defects. As the growth temperature was further increased, the hexagonal phase tvas found to be dominant in the deposited InN film.
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.
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.
Optical and electrical investigations of isoelectronic In-doped GaN films
(2000)
Shu, CK
;
Lee, WH
;
Pan, YC
;
Chen, CC
;
Lin, HC
The optical and electrical properties of isoelectronic In-doped GaN films grown by metalorganic vapor phase epitaxy (MOVPE) were investigated by X-ray, photoluminescence (PL), Hall and Raman measurements. As a result, adequate In-doping quantity causes not only a reduction of yellow luminescence and unintentional background concentration, but an enhanced mobility and decrease in the widths. The improved crystalline and optical qualities of GaN films may be attributed to the decrease in defects. (C) 2000 Elsevier Science Ltd. All rights reserved.
Time-resolved photoluminescence study of isoelectronic In-doped GaN films grown by metalorganic vapor-phase epitaxy
(2000-05-29)
Huang, HY
;
Shu, CK
;
Lin, WC
;
Chuang, CH
;
Lee, MC
Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of the donor-bound-exciton transition of undoped GaN exhibits a strong dependence on temperature. When In is doped into the film, the recombination lifetime decreases sharply from 68 to 30 ps, regardless of the measured temperature and In source flow rate. These observations might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process. (C) 2000 American Institute of Physics. [S0003- 6951(00)02622-X].
Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition
(2000-10-30)
Huang, HY
;
Lin, WC
;
Lee, WH
;
Shu, CK
;
Liao, KC
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor-acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I-2) transition in undoped GaN increases with temperature as T-1.5. However, the I-2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. (C) 2000 American Institute of Physics. [S0003-6951(00)01941-0].
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.

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