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Title: Degradation mechanism beyond device self-heating in high power light-emitting diodes
Authors: Yung, KCW 
Liem, H
Choy, HS
Lun, WK
Issue Date: 1-May-2011
Source: Journal of applied physics, 1 May 2011, v. 109, no. 9, 094509, p. 1-6
Abstract: A unique degradation property of high power InGaN/GaN multiple quantum well (MQW) white light-emitting diodes (LEDs) was identified. The LEDs were stressed under different forward-currents. The various ageing characteristics were analyzed for both the electrical response and electro-luminescence (EL) spectra. The Raman spectroscopy allowed noninvasive probing of LED junction temperature profiles which correlated well with the EL characteristics, showing a junction temperature drop during degradation at certain current levels. In addition to the common observations: (1) a broadening of the light intensity-current (L-I) characteristic in the nonlinear regime, and (2) a shift of the current-voltage (I-V) dependence to higher current levels, the EL spectra showed different temperature responses of the two blue emission peaks, 440 and 463 nm. The former was temperature sensitive and thus related to shallow defect levels, while the latter was thermally stable and deeper defect states were involved in the degradation process. This unique selection rule resulted in the enhancement of the blue emission peak at 463 nm after degrading the LEDs. This study suggests that LED device heating is not directly linked to the degradation process.
Keywords: Ageing
Defect states
Gallium compounds
III-V semiconductors
Indium compounds
Light emitting diodes
Raman spectra
Semiconductor quantum wells
Wide band gap semiconductors
Publisher: American Institute of Physics
Journal: Journal of applied physics 
ISSN: 0021-8979
EISSN: 1089-7550
DOI: 10.1063/1.3580264
Rights: © 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in K. C. Yung et al., J. Appl. Phys. 109, 094509 (2011) and may be found at
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