Browsing by Author "Yang, M. D."

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Carrier Dynamics in InAs/GaAs Quantum Rings
(2009)
Lin, C. H.
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Ling, H. S.
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Sun, K. W.
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Lee, C. P.
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Lin, S. D.
We have investigated the temperature dependence of the carrier relaxation dynamics in InAs/GaAs self-assembled quantum rings by using the time-resolved photoluminescence technique with a time resolution of similar to 250 ps. The carrier relaxation in the QRs not only shows strong dependence on the lattice temperature, it is also significant slower than the carrier relaxation in the quantum dots at temperature above 150 K.
Density-dependent energy relaxation of hot electrons in InN epilayers
(2009-01-01)
Yang, M. D.
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Liu, Y. W.
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Shen, J. L.
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Chen, C. W.
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Chi, G. C.
This work investigates the dependence of the hot-electron energy relaxation in InN epilayers on electron density. From the high-energy tail of photoluminescence, the electron temperature of the hot electrons was determined. Acoustic phonons have an important role in the energy relaxation of the hot electrons. The density-dependent electron energy loss rate in InN can be explained by a combination of longitudinal optical and acoustic phonon emissions. A slowing of energy loss rate at high electron densities was observed and attributed to piezoelectric coupling to acoustic phonons. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056383]
Effects of rapid thermal annealing on the structural properties of TiO(2) nanotubes
(2011-10-15)
Lin, J. Y.
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Chou, Y. T.
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Shen, J. L.
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Yang, M. D.
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Wu, C. H.
The structural properties of TiO(2) nanotubes with rapid thermal annealing (RTA) and traditional thermal annealing in O(2) were studied by X-ray diffraction (XRD) and Raman scattering measurements. From analyzing the line width of XRD and the correlation length of the Raman peak, we demonstrate that RTA can be an effective tool for amorphous-anatase transformation in TiO(2) nanotubes. The Raman peak redshifts and reduces its line width after thermal annealing and RTA, which may involves the reduction of oxygen-related defects. (C) 2011 Elsevier B. V. All rights reserved.
Effects of rapid thermal annealing on the structural properties of TiO2 nanotubes
(2011-10-15)
Lin, J. Y.
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Chou, Y. T.
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Shen, J. L.
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Yang, M. D.
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Wu, C. H.
The structural properties of TiO2 nanotubes with rapid thermal annealing (RTA) and traditional thermal annealing in O-2 were studied by X-ray diffraction (XRD) and Raman scattering measurements. From analyzing the line width of XRD and the correlation length of the Raman peak, we demonstrate that RTA can be an effective tool for amorphous-anatase transformation in TiO2 nanotubes. The Raman peak redshifts and reduces its line width after thermal annealing and RTA, which may involves the reduction of oxygen-related defects. (C) 2011 Elsevier B. V. All rights reserved.
Improvement of luminescence from Si nanocrystals with thermal annealing in CO2
(2008-01-15)
Yang, M. D.
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Chu, A. H. M.
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Shen, J. L.
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Huang, Y. H.
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Yang, T. N.
Photoluminescence (PL) of Si nanocrystals with annealing in CO2 was studied using the continuous and time-resolved PL measurements. The PL intensity enhances as annealing temperature increases, which is attributed to passivation of the nonradiative recombination centers. As the annealing temperature is 950 degrees C the PL intensity has a maximum value, which increases about a factor of 3 than that of the untreated sample. Based on the emission energy dependence of the PL decay time, the depth of carrier localization is found to increase after the annealing in CO2. We suggest that the oxygen atoms desorbed from CO2 diffuse to react with Si nanocrystals and introduce localized states at the Si/SiO2 interface. (C) 2007 Elsevier B.V. All rights reserved.
Improving Performance of InGaN/GaN Light-Emitting Diodes and GaAs Solar Cells Using Luminescent Gold Nanoclusters
(2009)
Yang, M. D.
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Wu, S. W.
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Shu, G. W.
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Wang, J. S.
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Shen, J. L.
We studied the optoelectronic properties of the InGaN/GaN multiple-quantum-well light emitting diodes (LEDs) and single-junction GaAs solar cells by introducing the luminescent Au nanoclusters. The electroluminescence intensity for InGaN/GaN LEDs increases after incorporation of the luminescent Au nanoclusters. An increase of 15.4% in energy conversion efficiency is obtained for the GaAs solar cells in which the luminescent Au nanoclusters have been incorporated. We suggest that the increased light coupling due to radiative scattering from nanoclusters is responsible for improving the performance of the LEDs and solar cells. Copyright (C) 2009 M. D. Yang et al.
Measuring junction temperature of GaAs solar cells using pulse-width modulation photoluminescence
(2010-07-01)
Yang, M. D.
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Liao, W. C.
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Shu, G. W.
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Liu, Y. K.
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Shen, J. L.
A photoluminescence (PL) technique is presented to measure the junction temperature of GaAs solar cells. The technique utilizes the pulse-width modulation of excitation laser and the temperature dependence of PL spectra. The apparent change of PL energy on duty cycle can be advantageously used for the determination of the junction temperature. Varying the duty cycle from 10% to 75% causes an increase of 2.9 Kin the junction temperature of GaAs solar cells. The carrier temperature of the junction layer was studied to confirm the result obtained from the pulse-width modulation PL (C) 2010 Elsevier Ltd. All rights reserved.
Morphology and optical properties of zinc oxide thin films grown on Si (100) by metal-organic chemical vapor deposition
(2009-01-01)
Lan, S. M.
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Uen, W. Y.
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Chan, C. E.
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Chang, K. J.
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Hung, S. C.
Undoped zinc oxide (ZnO) thin films were deposited on Si (100) substrates by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD). After a nucleation layer of ZnO about 500 A... was deposited, top ZnO films with 320-440 nm in thickness were fabricated at temperatures varying from 450 to 600 A degrees C, respectively. X-ray diffraction analyses demonstrate that all the films grown have polycrystalline wurtzite structure. Scanning electron microscopy observations indicate that ZnO films grow with c-axis aligned grains when the deposition temperature is lower than 600 A degrees C. However, 3D microstructures without c-axis alignment were found when the film was deposited at 600 A degrees C. Room temperature photoluminescence (PL) spectra peaking at 3.27-3.29 eV were observed for the ZnO films grown at 450-600 A degrees C. However, only the spectrum from the film grown at 600 A degrees C could present a high intensity ratio of the ultraviolet band to deep-level emissions, which is above 392 and show a minimum full-width at half-maximum of 99 meV for the ultraviolet band. Temperature-dependent PL measurements from 20 to 300 K exhibited the luminescent mechanism of the present ZnO films to be near band excitonic emission.
Nonpolar light emitting diode made by m-plane n-ZnO/p-GaN heterostructure
(2011-12-01)
Chen, C. W.
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Hung, S. C.
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Lee, C. H.
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Tun, C. J.
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Kuo, C. H.
Nonpolar (100) m-plane n-ZnO/p-GaN light-emitting-diodes (LEDs) were grown by chemical vapor deposition on p-GaN templates which was grown by metalorganic chemical vapor deposition on LiAlO(2)(100) substrate. Direct current (DC) electroluminescence (EL) measurements yielded a peak at 458nm. The EL peak position was independent of drive current and a full width of half maximum (FWHM) of 21.8 nm was realized at 20mA. The current-voltage characteristics of these diodes showed a forward voltage (V(f)) of 6V with a series resistance of 2.2 x 10(5) Omega. (C) 2011 Optical Society of America
Optical studies of InN epilayers on Si substrates with different buffer layers
(2007-12-01)
Yang, M. D.
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Shen, J. L.
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Chen, M. C.
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Chiang, C. C.
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Lan, S. M.
We have investigated the photoluminescence (PL) and time-resolved PL from the InN epilayers grown on Si substrates with different buffer layers. The narrowest value of the full width at half maximum of the PL peak is 52 meV with the AlN/AlGaN/GaN triple buffer layer, which is better than previous reports on similar InN epilayers on Si substrates. Based on the emission-energy dependence of the PL decays, the localization energy of carriers is also the least for the InN with a triple buffer layer. According to the x-ray diffraction measurements, we suggest that the reduced lattice mismatch between the InN epilayer and the top buffer layer is responsible for improvement of sample quality using the buffer-layer technique. (c) 2007 American Institute of Physics.
Oxygen sensors made by monolayer graphene
(2012-01-01)
Hung, S. C.
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Chen, C. W.
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Yang, M. D.
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Yeh, C. W.
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Wu, C. H.
The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O-2) at room temperature. The monolayer graphene, grown by chemical vapor deposition (CVD) with perfect uniformity within 1cmx1cm will attach O-2 molecules which will act as a p-type dopant and enhance the hole conductivity, make a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O-2 concentration and the detection limit of the simple O-2 sensor was 1.25% in volume ratio.
Oxygen sensors made by monolayer graphene under room temperature
(2011-12-12)
Chen, C. W.
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Hung, S. C.
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Yang, M. D.
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Yeh, C. W.
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Wu, C. H.
The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O(2)) at room temperature. The monolayer graphene, grown by chemical vapor deposition with perfect uniformity within 1 cm x 1 cm will attach O(2) molecules and enhance the hole conductivity, which will lead to a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O(2) concentration and the detection limit of the simple O(2) sensor was 1.25% in volume ratio. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3668105]
Performance Evaluation of Constructed Facilities through Linguistic Judgment
(2009)
Pan, N. F.
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Dzeng, R. J.
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Yang, M. D.
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土木工程學系
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Department of Civil Engineering
It is often difficult to estimate exact probabilities of occurrence of fault events for the use in the conventional fault tree analysis (FTA) when failure data are insufficient or fault events are vague such as human error. A hybrid approach utilizing fuzzy sets and possibility theory is presented to overcome this problem. In the approach, failure possibilities of imprecise events are characterized by fuzzy sets to translate expert subjective judgments while fuzzy fault rates are derived from fuzzy possibility scores based on a modified possibility transformation function. An example of beam failure is presented to demonstrate the capability of the approach that can assist safety engineers to effectively assess fault possibilities and better analyze building performance.
Temperature dependence of time-resolved photoluminescence spectroscopy in InAs/GaAs quantum ring
(2009-05-04)
Lin, C. H.
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Lin, H. S.
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Huang, C. C.
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Su, S. K.
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Lin, S. D.
We present detailed experimental results of the temperature dependence of continuous wave and time-resolved photoluminescence (PL) spectroscopy in self-assembled InAs/GaAs quantum dot and quantum ring nanostructures. A dramatic increase in PL decay time of the excited and ground states is observed in InAs quantum rings at high temperature. We speculate that the longer PL lifetime in quantum rings is due to the interplay among the dark states, ground states, and the reduced wave function overlapping between electrons and holes. A rate equation model is proposed to interpret the observed temperature dependence of the ground state exciton lifetime.