Analysis of degradation mechanisms in GaN-based light-emitting diodes under reverse-bias stress: effects of defects and junction-temperature increase

Abstract

Degradation phenomena of GaN-based blue LEDs are investigated from comprehensive electrical, optical, and thermal analyses. After constant reverse-bias stress, the LED sample under investigation shows permanent degradations indicated by increases both in the tunneling/sidewall leakage current in the low-current region and the nonradiative current in the high-current region. A subsequent decrease in series resistance and increase in junction temperature are also observed. The degradation at high currents is analyzed in terms of the radiative recombination current utilizing the information of the internal quantum efficiency (IQE), which has been rarely attempted. All of the observed degradations can be attributed to the increase in defect density in the active layer of the LED chip under reverse-bias stress. This work emphasizes that many important reliability-related features of LEDs are functions of defects and the junction temperature and that the IQE can provide crucial information in the analysis. The increased junction temperature would have further detrimental effects on the device performance and eventually lead to device failure. The analyses presented in this work shed more light on understanding the degradation phenomena in the GaN-based LEDs under reverse-bias stress.