Browsing by Author "Huang, Sheng Bang"

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Accelerated Degradation of High Power Light-Emitting Diode Resulted from Inhomogeneous Current Distribution
(2011-03-01)
Yang, Shih Chun
;
Lin, Pang
;
Fu, Han Kuei
;
Lee, An Tse
;
Chen, Tzung Te
The uniformity of current spreading is one of the key points to inspect the reliability and endurance of InGaN-based light-emitting diodes. In this paper, we propose an effective circuit model to analyze the phenomenon of premature turn-on diodes in the active layer. With the aging tests and novel investigation of failure analyses, the simulating results are good agreement with experimental data. It is found that an inhomogeneous distribution of forward current in light-emitting diode chips, as measured by conductive atomic force microscopes, provides the evidence that V-shaped defects and the associated threading dislocations are electrically active. Furthermore, the results of emission microscopy images and transmission electron microscope reviews support the assumption that the threading dislocations associated with V-shaped defects behave as very small shunt resistors connected across p-n junction. This study provides a degradation mechanism to realized one of the failure modes of high power light-emitting diodes. (C) 2011 The Japan Society of Applied Physics
Failure and degradation mechanisms of high-power white light emitting diodes
(2010-07-01)
Yang, Shih-Chun
;
Lin, Pang
;
Wang, Chien-Ping
;
Huang, Sheng Bang
;
Chen, Chiu-Ling
The investigation explores the factors that influence the long-term performance of high-power 1 W white light emitting diodes (LEDs). LEDs underwent an aging test in which they were exposed to various temperatures and electrical currents, to identify both their degradation mechanisms and the limitations of the LED chip and package materials. The degradation rates of luminous flux increased with electrical and thermal stresses. High electric stress induced surface and bulk defects in the LED chip during short-term aging, which rapidly increased the leakage current. Yellowing and cracking of the encapsulating lens were also important in package degradation at 0.7 A/85 degrees C and 0.7 A/55 degrees C. This degradation reduced the light extraction efficiency to an extent that is strongly related to junction temperature and the period of aging. junction temperatures were measured at various stresses to determine the thermal contribution and the degradation mechanisms. The results provided a complete understanding of the degradation mechanisms of both chip and package, which is useful in designing highly reliable and long-lifetime LEDs. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
Variation of Electrostatic Discharge Robustness Induced by the Surface Morphology of High Power Light-Emitting Diodes
(2010-05-01)
Yang, Shih Chun
;
Lin, Pang
;
Fu, Han Kuei
;
Wang, Chien Ping
;
Chen, Tzung Te
The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge (ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate. Accordingly, the investigation of ESD failure mechanisms is a beneficial topic. However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short period. Before the series ESD stress, atomic force microcopy (AFM) and conductive AFM (C-AFM) were applied to explore the correlation between surface morphology and electrical properties of LED chips. Furthermore, after the series ESD stress, transmission electron microscopy (TEM) was used to investigate the failure modes and compare to the distribution of the surface current observed by C-AFM. These findings suggest that the V-shaped defect and surface morphology are strong correlate to the endurance of ESD stress. (c) 2010 The Japan Society of Applied Physics