Browsing by Author "Shu, CK"

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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.
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.
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.
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.
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.
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].
Isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition
(1999-08-03)
Shu, CK
;
Ou, J
;
Lin, HC
;
Chen, WK
;
Lee, MC
The isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition was investigated by using Raman scattering, scanning electron microscopy (SEM), and x-ray and photoluminescence (PL) measurements. In our study, the phonon spectra of films remain sharp without alloy formation after incorporation of small amounts of In atoms. The SEM pictures of the sample surface reveal greatly reduced nanopits indicating better surface flatness that is also supported by the multiple interference effect in the PL signals. More importantly, isoelectronic doping has caused the linewidth at 15 K of the near-band-edge emission of GaN to decrease sharply to 10 meV or less, reflecting improved optical property. (C) 1998 American Institute of Physics. [S0003-6951(98)01331-X].
Isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition
(1998-08-03)
Shu, CK
;
Ou, J
;
Lin, HC
;
Chen, WK
;
Lee, MC
The isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition was investigated by using Raman scattering, scanning electron microscopy (SEM), and x-ray and photoluminescence (PL) measurements. In our study, the phonon spectra of films remain sharp without alloy formation after incorporation of small amounts of In atoms. The SEM pictures of the sample surface reveal greatly reduced nanopits indicating better surface flatness that is also supported by the multiple interference effect in the PL signals. More importantly, isoelectronic doping has caused the linewidth at 15 K of the near-band-edge emission of GaN to decrease sharply to 10 meV or less, reflecting improved optical property. (C) 1998 American Institute of Physics.
Luminescence intensity reduction in Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2001-04-01)
Shu, CK
;
Chen, HH
;
Lee, WH
;
Pan, YC
;
Huang, HY
Photoluminescence dynamic responses of a heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy have been investigated. As the probe power density increased from 2.5 to 925 W/cm(2), a Mg-related emission band shifted from 2.82 to 3.16 eV revealing characteristics of donor-acceptor pair recombination. The intensity evolution also showed slow decay that suggests the metastable emission behavior. A simple potential barrier model was proposed to occur between the Mg related deep levels and common Mg acceptor level, which impedes electron relaxation and thus slows down the luminescence decay. From the variation of decay time constant with temperature. a barrier energy was deduced to be about 69 meV which is very close to the electrical result of 68 meV.
Metastable photoluminescence in heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2000)
Shu, CK
;
Lee, WH
;
Pan, YC
;
Huang, HY
;
Chen, HH
The long-term transient spectra of heavily Mg-doped GaN have been investigated. As the excitation power density increased, the broad Mg-induced emission band showed blue-shift revealing characteristic of donor-acceptor pair (DAP) recombination. We also observed an unusually slow intensity decay. The characteristic time constants range from several tenths to a few hundred seconds for emission between 360 and 460 nm. Our results are interpreted in terms of metastability due to compounded effects of differential DAP population and recombination rates and uneven acceptor distribution.
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.
Phonon-plasmon interaction in GaN films studied by Raman scattering
(1998-02-01)
Shen, CC
;
Shu, CK
;
Lin, HC
;
Chen, WK
;
Chen, WH
GaN films of different buffer thicknesses (from 0 to 600 Angstrom) were grown on (0001) sapphire using MOCVD. The epitaxial films show autodoping with carrier concentration ranging from 8 x 10(16) to 5 x 10(17) cm(-3) as determined by Hall measurements. The Raman scattering reveals that the A(1)(LO) mode shifts from 733 to 740 cm(-1) as a result of the phonon-plasmon interaction.
Photoluminescence and photoluminescence excitation studies of as-grown and P-implanted GaN: On the nature of yellow luminescence
(2002-05-06)
Huang, HY
;
Chuang, CH
;
Shu, CK
;
Pan, YC
;
Lee, WH
We have studied optical and electronic properties of isoelectronic P-implanted GaN films grown by metalorganic chemical vapor phase epitaxy. After rapid thermal annealing, a strong emission band around 430 nm was observed, which is attributed to the recombination of exciton bound to isoelectronic P-hole traps. From the Arrhenius plot, the hole binding energy of similar to180 meV and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, the implantation process likely introduced N(I) and P-related defects. By using photoluminescence excitation technique, we found that the P-implantation-induced localized states not only increase the yellow luminescence but also suppress the transitions from the free carriers to deep levels. (C) 2002 American Institute of Physics.
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.
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.
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.
Raman and x-ray studies of InN films grown by metalorganic vapor phase epitaxy
(1998-11-02)
Lee, MC
;
Lin, HC
;
Pan, YC
;
Shu, CK
;
Ou, J
Thin InN films were deposited on the (0001) sapphire substrate at various temperatures from 325 to 600 degrees C by metalorganic vapor phase epitaxy. We used Raman scattering and x-ray diffraction to investigate the film properties and crystalline structures. Significant line broadening, softening and intensity evolution were observed at the growth temperatures between 375 and 450 degrees C. This can be attributed to the formation of the mixed hexagonal and cubic structures and the related dislocation defects. As the growth temperature is further increased, the hexagonal phase is found to be dominant in the deposited InN film. (C) 1998 American Institute of Physics. [S0003-6951(98)00744-X].
The effects of isoelectronic in-doping in GaN films grown by MOCVD
(1998)
Shu, CK
;
Ou, J
;
Lin, HC
;
Pan, YC
;
Lee, WH
The isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition (MOCVD) was investigated by using Raman scattering, scanning electron microscopy (SEM), Hall, Xray and photoluminescence (PL) measurements. In our study, after incorporating small amounts of In atoms into GaN compound (less than 0.4%, thus no alloy), SEM pictures showed improved surface smoothness with greatly reduced nano-pits, which was also confirmed by the multiple interference effects in PL spectra. Doping of adequate quantity caused the reduction of yellow luminescence and unintentional background concentration, and the line width shrinkage in X-ray, PL and Raman data, and the enhanced mobility. The improved crystalline and optical qualities of GaN:In films may be attributed to the decrease in dislocation density that may be related to the "impurity softening" phenomena.
The electronic structure and optical properties of phosphorus implanted GaN films
(2000)
Shu, CK
;
Lee, WH
;
Huang, HY
;
Chuang, CH
;
Chen, WK
We have studied optical and electronicc transition properties of GaN layers grown by MOCVD which are implanted by isoelectronic impurities of phosphorus (P). The P-implanted samples were treated by rapid thermal annealing to recover implantation-induced damages. A strong emission band around 430 nm were observed in P-implanted sample due to the recombination of bound exciton to P-hole isoelectronic traps. From the Arrhenius plot, the hole binding energy about 180 meV localized at the P-isoelectronic trap and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, we suggest that the implantation likely induces N-I or P-related defects. From the PLE, we found that the absorption by band-to-band and shallow donors dominates the yellow luminescence (YL) and the implantation of P has induced localized states that not only increase the YL but also suppress the transition from the free electron-hole pairs to the deep-levels.
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].