Progressive current degradation and breakdown behavior in GaN LEDs under high reverse bias stress**Project supported by the National Natural Science Foundation of China (Grant Nos. 61504050 and 11604124), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20140168 and BK20150158), and the Fundamental Research Funds for the Central Universities, China (Grant Nos. JUSRP51628B and JUSRP51510).

Abstract

The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reverse-bias stress are studied by combining the electrical, optical, and surface morphology characterizations. The current features a typical “soft breakdown” behavior, which is linearly correlated to an increase of the accumulative number of electroluminescence spots. The time-to-failure for each failure site approximately obeys a Weibull distribution with slopes of about 0.67 and 4.09 at the infant and wear-out periods, respectively. After breakdown, visible craters can be observed at the device surface as a result of transient electrostatic discharge. By performing focused ion beam cuts coupled with scan electron microscope, we observed a local current shunt path in the surface layer, caused by the rapid microstructure deterioration due to significant current heating effect, consistent well with the optical beam induced resistance change observations.