Degradation mechanisms in GaN/AlaN/InGaN LEDs and LDs

Our studies of device lifetime and the main degradation mechanisms in Nichia blue LEDs date back to spring 1994. Following the initial studies of rapid failures under high current electrical pulses, where metal migration was identified as the cause of degradation, we have placed a number of Nichia NLPB-500 LEDs on a series of life tests. The first test ran for 1000 hours under normal operating conditions (20 mA at 23/spl deg/C). As no noticeable degradation was observed, a second 23/spl deg/C test was performed with the same devices but with a range of currents between 20 and 70 mA. For subsequent tests, the temperature was increased by 10/spl deg/C in 500 h intervals up to a final temperature of 95/spl deg/C using the same currents applied in the second test. This work presents a thermal degradation mechanism that dominates degradation at high ambient temperatures.