DEGRADATION MECHANISMS IN ALGAN INGAN/GAN LIGHT-SOURCES/

Our investigations of device Lifetime and the main degradation mechani sms in Nichia blue LEDs date back to Spring 1994. Following the initia l studies of rapid failures under high current electrical pulses, wher e 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 m A at 23 degrees C). As no noticeable degradation was observed, the sec ond room temperature test involved the same devices but with a range o f currents between 20 and 70 mA. After 1600 hours, some degradation wa s observed in devices driven at 60 and 70 mA, but it was still less th an 20%. The subsequent tests, still underway, included stepping up the temperature by 10 degrees C in 500 h intervals, with currents the sam e as in the second test. This work reviews the failure analysis that w as performed on the degraded devices and the degradation mechanisms th at were identified. Also, preliminary data on high current degradation of quantum-well LEDs is reported.