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Materials 2014, 7(5), 3758-3771; doi:10.3390/ma7053758
Article

Effects of Asymmetric Quantum Wells on the Structural and Optical Properties of InGaN-Based Light-Emitting Diodes

*  and
Department of Electronic Engineering and Green Technology Research Center, Chang Gung University, Taoyuan 333, Taiwan
* Author to whom correspondence should be addressed.
Received: 8 December 2013 / Revised: 17 January 2014 / Accepted: 29 April 2014 / Published: 12 May 2014
(This article belongs to the Section Structure Analysis and Characterization)
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Abstract

A metalorganic vapor phase epitaxy-grown InGaN/GaN multiple-quantum-well (MQW) with three graded-thickness wells (the first-grown well had the greatest width) near the n-GaN was used as the active layer of an LED. For LEDs with an asymmetric quantum well (AQW), high-resolution X-ray diffraction and transmission electron microscopic reveal that the modified MQWs with a reasonable crystalline quality were coherently strained on the underlying GaN epilayers without any relaxation. In addition, the slight increase of indium segregation in the LED with an AQW may be attributed to variations in indium contents experienced during epitaxial growth of the wide well-containing MQWs. By preventing the energetic electrons from accumulating at the topmost quantum well nearest the p-GaN, the presence of light intensity roll-off in the LED with an AQW is shifted to higher currents and the corresponding maximum light output power is increased with a ratio 7.9% higher than that of normal LEDs. Finally, similar emission wavelengths were observed in the electroluminescence spectra of both LEDs, suggesting that light emitted mostly from the top quantum wells (near the p-GaN) while the emissions from the AQW region were insignificant.
Keywords: InGaN; asymmetric quantum well (AQW); light-emitting diodes (LEDs) InGaN; asymmetric quantum well (AQW); light-emitting diodes (LEDs)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Tsai, C.-L.; Wu, W.-C. Effects of Asymmetric Quantum Wells on the Structural and Optical Properties of InGaN-Based Light-Emitting Diodes. Materials 2014, 7, 3758-3771.

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