Browsing by Author "Tsai, J. Y."

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Improvement of efficiency and ESD characteristics of ultraviolet light-emitting diodes by inserting AlGaN and SiN buffer layers
(2007-07-01)
Huang, G. S.
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Kuo, H. C.
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Lo, M. H.
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Lu, T. C.
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Tsai, J. Y.
We have studied the effect of the AlGaN insertion and SiN buffer layers of ultraviolet light-emitting diodes (UVLEDs) on efficiency and electrostatic discharge (ESD) characteristics of UVLEDs grown by metalorganic chemical vapor deposition. The etching pit density was reduced from 3.6 x 10(8) cm(-2) in conventional samples to 1.6 x 10(7) cm(-2) in UVLEDs grown with the AlGaN insertion layer and SiN buffer layer. During the ESD tests at the negative biases of 3000 V, the live percentage of UVLEDs increased from 67% in conventional samples to 86% in samples with AlGaN insertion layers and SiN buffer layers. In addition, the device shows a low leakage current of 1.1 x 10(-8) A at -5 V and the light output power was 70% higher than the conventional UVLEDs at an injection current of 20 mA. (c) 2007 Elsevier B.V. All rights reserved.
Investigation of GaN-based light emitting diodes with nano-hole patterned sapphire substrate (NHPSS) by nano-imprint lithography
(2009-08-25)
Huang, H. W.
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Lin, C. H.
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Huang, J. K.
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Lee, K. Y.
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Lin, C. F.
In this paper, gallium-nitride (GaN)-based light-emitting diodes (LEDs) with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated and investigated. At an injection current of 20mA, the LED with NHPSS increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.33, and the wall-plug efficiency is 30% higher at 20mA indicating that the LED with NHPSS had larger light extraction efficiency. In addition, by examining the radiation patterns, the LED with NHPSS shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography. (C) 2009 Elsevier B.V. All rights reserved.
Optical properties of InGaN quantum dots grown by SiN(x) nanomasks
(2007-04-15)
Huang, L. L.
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Chang, H. J.
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Chou, Y. Y.
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Wang, C. H.
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Chen, T. T.
InGaN quantum dots (QDs) deposited on SiN(x) nanomasks have been investigated by atomic force microscopy, photoluminescence (PL), and photoluminescence excitation (PLE) measurements. It was found that the size of QDs can be well controlled by SiN(x) nanomasks, enabling the manipulation of quantum confinement effect. The PL spectra of InGaN QDs contain several fine structures, and the main peaks can be attributed to families of QDs with different sizes. The emission arising from InGaN QDs and GaN buffer layer can be clearly distinguished based on PLE measurement, which can be used to improve the interpretation in the previous reports. Our study indicates that the quantum confined Stark effect due to piezoelectric field plays a very important role in the optical properties of InGaN QDs, which is very useful for the application of optoelectronic devices.(c) 2007 American Institute of Physics.
Optically modulated internal strain in InGaN quantum dots grown on SiNx nano masks
(2008-01-21)
Chang, H. J.
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Chen, T. T.
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Huang, L. L.
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Chen, Y. F.
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Tsai, J. Y.
Optically modulated internal strain has been observed in InGaN quantum dots (QDs) deposited on SiNx nano masks. The modulated internal strain can induce a number of intriguing effects, including the change of refractive index and the redshift of InGaN A(1)(LO) phonon. The underlying mechanism can be well accounted for in terms of the variation of internal strain through the converse piezoelectric effect arising from the screening of the internal electric field due to spatial separation of photoexcited electrons and holes. Our results point out a convenient way for the fine tuning of physical properties in nitride-based semiconductor nanostructures, which is very important for high quality optoelectronic devices. (c) 2006 Optical Society of America.