Browsing by Author "Kuo, S. Y."

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Effect of nitrogen contents on the temperature dependence of photoluminescence in InGaAsN/GaAs single quantum wells
(2006-07-01)
Lai, Fang-I
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Kuo, S. Y.
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Wang, J. S.
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Kuo, H. C.
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Wang, S. C.
A series of InGaAsN/GaAs single-quantum wells (SQWs) with N contents varied from 0% to 5.3% were grown by molecular-beam epitaxy using a solid As and a nitrogen plasma sources. The impact of nitrogen concentration on the optical properties, as determined by the temperature dependence of photoluminescence (PL), of a 6 nm SQW was investigated. In the low-temperature region, a pronounced temperature-dependent S-shaped peak position was observed in PL spectra while increasing the nitrogen concentration. Quenching behavior reveals that the defect-related nonradiative processes might be enhanced in the highly nitrogen incorporated samples and thus influence the recombination dynamics. In addition, the evolution of the peak position of the InGaAsN/GaAs samples was in agreement with the empirical Varshni model in the high-temperature region. A significant reduction in the temperature dependence of the emission peak position is analyzed as well, and further confirms the prediction of proposed band anticrossing model of the electronic structure of III-N-V alloys. (c) 2006 American Vacuum Society.
Investigation of GaN-based light-emitting diodes using double photonic crystal patterns
(2011-02-01)
Huang, H. W.
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Lai, Fang-I
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Kuo, S. Y.
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Huang, J. K.
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Lee, K. Y.
GaN-based LEDs with photonic crystal (PhC) patterns on an n- and a p-GaN layer by nano-imprint lithography (NIL) are fabricated and investigated. At a driving current of 20 mA on Transistor Outline (TO)-can package, the light output power of the GaN-based LED with PhC patterns on an n- and a p-GaN layer is enhanced by a factor of 1.30, and the wall-plug efficiency is increased by 24%. In addition, the higher output power of the LED with PhC patterns on the n- and p-GaN layer is due to better crystal quality on n-GaN and higher scattering effect on p-GaN surface using PhC pattern structure. (C) 2010 Elsevier Ltd. All rights reserved.
Investigation of GaN-based vertical-injection light-emitting diodes with GaN nano-cone structure by ICP etching
(2008-07-25)
Huang, H. W.
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Lin, C. H.
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Yu, C. C.
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Lee, K. Y.
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Lee, B. D.
The GaN-based thin-film vertical-injection LEDs (VLEDs) with GaN nano-cone structures are fabricated and presented. Under the process conditions of fixed Cl(2)/Ar now rate of 10/25sccm and ICP/bias power of 200/200W, the GaN nano-cone structures are self-assembly formed with variable density of 1.5 x 10(7) to 1.4 x 10(1) cm(-2) and variable depth of 0.56-1.34 mu m when varying the ICP chamber pressure. At a driving current of 350mA and with chip size of 1 mm x 1 mm, the light output power of our thin-film LED with a specific GaN nano-cone structure reaches 224 mW which is enhanced by 160% when compared with the output power of conventional VLED. In addition, the corresponding light radiation pattern Shows Much higher light intensity Clue to the strong light scattering effect by the formed nano-cone Structure. (C) 2008 Elsevier B.V. All rights reserved.
Optical properties of a-plane InGaN/GaN multiple quantum wells on r-plane sapphire substrates with different indium compositions
(2009-03-15)
Chiu, C. H.
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Kuo, S. Y.
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Lo, M. H.
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Ke, C. C.
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Wang, T. C.
A-plane In(x)Ga(1-x)N/GaN (x=0.09, 0.14, 0.24, and 0.3) multiple-quantum-wells (MQWs) samples, with a well width of about 4.5 nm, were achieved by utilizing r-plane sapphire substrates. Optical quality was investigated by means of photoluminescence (PL), cathodoluminescence, and time resolved PL measurements (TRPL). Two distinguishable emission peaks were examined from the low temperature PL spectra, where the high- and low-energy peaks were ascribed to quantum wells and localized states, respectively. Due to an increase in the localized energy states and absence of quantum confined Stark effect, the quantum efficiency was increased with increasing indium composition up to 24%. As the indium composition reached 30%, however, pronounced deterioration in luminescence efficiency was observed. The phenomenon could be attributed to the high defect densities in the MQWs resulted from the increased accumulation of strain between the InGaN well and GaN barrier. This argument was verified from the much shorter carrier lifetime at 15 K and smaller activation energy for In(0.3)Ga(0.7)N/GaN MQWs. In addition, the polarization-dependent PL revealed that the degree of polarization decreased with increasing indium compositions because of the enhancement of zero-dimensional nature of the localizing centers. Our detailed investigations indicate that the indium content in a-plane InGaN/GaN MQWs not only has an influence on optical performance, but is also important for further application of nitride semiconductors.
"S-shaped" Photoluminescence Emission Shift in Cu(In,Ga)Se-2 Thin Films
(2012)
Liao, Y. K.
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Kuo, S. Y.
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Lai, F. I.
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Lin, W. T.
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Hsieh, D. H.
We have utilized photoluminescence (PL) measurement to investigate carrier recombination mechanism in Cu(In,Ga)Se-2 thin films and observed an S-shaped emission shift revealed from the corresponding PL peak of near band edge transition.