Browsing by Author "Lin, Der-Yuh"

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Effect of Thermal Annealing on a-plane GaN Grown on r-plane Sapphire
(2014)
Ko, Tsung-Shine
;
Lu, Tien-Chang
;
Chen, Jung-Ron
;
Ou, Sin-Liang
;
Chang, Chia-Ming
The crystal quality improvement of a-plane GaN grown on r-plane sapphire was demonstrated by applying thermal annealing on as-grown samples in nitrogen ambient. The root mean square roughness of the 1000 degrees C-annealed a-plane GaN was only 0.4 nm measured by atomic force microscopy. Transmission electron microscopy results further indicate threading dislocations were decreased from 5x10(10) cm(-2) to 1.5x10(10) cm(-2) along [0001] GaN and stacking faults were decreased from 8.7x 10(5) cm(-1) to 4.8x 10(5) cm(-1) after the sample was annealed at 1000 degrees C. Room temperature photo luminescence measurements showed band edge emission intensity was enhanced up to 2.6 folds compared to the regular a-plane GaN film. Furthermore, corresponding cathode luminescence images reveal larger emission area for a-plane GaN with annealing than those without annealing, which was attributed to reduction of the nonradiative recombination centers. A series of experiments confirm this annealing process could be useful for further applications of GaN-based optoelectric devices.
Optical and Electrical Characterizations of ZnMnO Thin Films on c-Al(2)O(3)
(2009-04-01)
Lin, Hung-Ji
;
Lin, Der-Yuh
;
Wu, Jenq-Shinn
;
Yang, Chu-Shou
;
Chou, Wu-Ching
We have studied the manganese (Mn) composition dependence of the optical and electrical properties of ZnMnO thin films, which are grown on c-Al(2)O(3) substrates by plasma-assisted molecular beam epitaxy (PAMBE). The lattice constant and grain size are estimated by Xray diffraction (XRD), and it is found that the lattice constant increases and the grain size decreases with increasing Mn composition. When more Mn is incorporated into the ZnMnO thin films, a blue shift of the absorption edges and photoluminescence emission peaks are observed. Hall measurement shows n-type conduction behavior for all the samples. The decrease in mobility might be related with the increase in the number of impurity scattering centers, and the decrease in the carrier concentration can be attributed to the carrier quenching effect induced by the deep-level defects. The ac electrical response of ZnMnO is studied by impedance spectroscopy (IS). The equivalent RC circuit and parameters of the grain and grain boundary are determined. (C) 2009 The Japan Society of Applied Physics
Optical and Electrical Characterizations of ZnMnO Thin Films on c-Al2O3
(2009-04-01)
Lin, Hung-Ji
;
Lin, Der-Yuh
;
Wu, Jenq-Shinn
;
Yang, Chu-Shou
;
Chou, Wu-Ching
We have studied the manganese (Mn) composition dependence of the optical and electrical properties of ZnMnO thin films, which are grown on c-Al2O3 substrates by plasma-assisted molecular beam epitaxy (PAMBE). The lattice constant and grain size are estimated by Xray diffraction (XRD), and it is found that the lattice constant increases and the grain size decreases with increasing Mn composition. When more Mn is incorporated into the ZnMnO thin films, a blue shift of the absorption edges and photoluminescence emission peaks are observed. Hall measurement shows n-type conduction behavior for all the samples. The decrease in mobility might be related with the increase in the number of impurity scattering centers, and the decrease in the carrier concentration can be attributed to the carrier quenching effect induced by the deep-level defects. The ac electrical response of ZnMnO is studied by impedance spectroscopy (IS). The equivalent RC circuit and parameters of the grain and grain boundary are determined. (C) 2009 The Japan Society of Applied Physics
Photoluminescence characterization of type-II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures
(2007-04-01)
Shiu, Jian-Jhin
;
Chen, Wei-Li
;
Lin, Der-Yuh
;
Yang, Chu-Shou
;
Chou, Wu-Ching
The optical characterization of type-II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures has been studied using photoluminescence (PL), temperature-dependent PL, and power-dependent PL. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe multiple quantum wells (MQWs) is type II. In comparison with the theoretical calculation based on solving the Schrodinger equation of a square potential well, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blue shift on increasing the excitation power. The blue shift can be interpreted in terms of the band-bending effect due to spatially separated carriers in a type-II alignment and the band filling effect. The thermal activation energy (EA) for quenching the PL intensity was determined from temperature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe or ZnSeTe layers decreased.