Browsing by Author "Hong, TM"

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Carrier generation mechanisms for photoconductivity in conjugated polymers
(2000-04-15)
Meng, HF
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Hong, TM
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物理研究所
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Institute of Physics
We study theoretically the origin of photoconductivity in conjugated polymers. The charge carriers are released when excitons dissociate through the deep levels within the semiconductor bandgap caused by either oxidation (carbonyl group) or structure defects. Our results explain the recent observations of the temperature-independent photocurrent in the sweep-out regime and the transient photocurrent at high excitation. The tightly bound exciton versus semiconductor band controversy on the photocarrier generation process is clarified.
Deep defect levels and exciton dissociation in conjugated polymers
(2001-09-01)
Meng, HF
;
Hong, TM
;
物理研究所
;
Institute of Physics
We study the localized deep electronic level within the bandgap of conjugated polymers in the presence of structure or oxygen (carbonyl group) defects. The structure defect is modeled as a chain twist, including the chain ends as a special case. Analytic expressions for both the energy and the wavefunction of the deep levels and the itinerant levels are obtained and supplemented by clear intuitive pictures. Carbonyl group is treated numerically within the tight-binding models. The rates of free carrier capture and exciton dissociation through the defect level via multi-phonon emission are calculated. We conclude that the defect dissociation dominates the intrinsic dissociation through thermal activation, and is the primary carrier generation mechanism in photoconductivity, Our results explain the photoconductivity enhancement due to oxidation, as well as the recent observation on the temperature-independent photocurrent in the sweep-out regime. (C) 2001 Elsevier Science B.V. All rights reserved.
Effect of nitrogen on diamond growth using unconventional gas mixtures
(1995-12-01)
Hong, TM
;
Chen, SH
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Chiou, YS
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Chen, CF
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交大名義發表
The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH4-CO2 by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH4-CO2 gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant ''cage-like'' structure with completed (100) facets. This result indicates that the continued addition of nitrogen gives rise to the deterioration of (111) facets and the retention of (100) facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C-2 emissions in the gas phase under optimum conditions.