High brightness GaN LEDs degradation during dc and pulsed stress

This paper reports an analysis of InGaN/GaN LEDs degradation under dc and pulsed current conditions. The analysis was carried out by means of current-voltage and optical power measurements, scanning electron microscopy and EDS maps. Identified degradation modes were leakage and generation/recombination current increase, series resistance increase and output power decrease, related to the high temperatures reached by the devices during stress. Failure analysis revealed degradation of anode contacts and Ti-W reflector, which can be related to the measured series resistance increase. Comparison between dc and pulsed stress carried out with the same average current indicated that pulsed driving does not imply an acceleration in the degradation rate, except for the lowest duty cycles.