Single-quantum well InGaN green light emitting diode degradation under high electrical stress

摘要

We performed a degradation study of high-brightness Nichi single-quantum well AlGaN/InGaN/GaN green light-emitting diodes (LEDs). The devices were subjected to high current electrical stress with current pulse amplitudes between 1 and 7 A and voltages between 10 and 70 V with a pulse length of 100 ns and a 1 kHz repetition rate. The study showed that when the current amplitude was increased above 6A, a fast (about 1 s) degradation occurred, with a visible discharge between the p- and n-type electrodes. Subsequent failure analysis revealed severe damage to the metal contacts, which lead to th eformation of shorts in the surface plane of the diode. For currents smaller than 6 A, a slow degradation was observed as a decrease in optical power and an increase in the reverse current leakage. However, a rapid degradation occurred between 24 and 100 h which was similar to the rapid degradation observed at higher current. The failure analysis results indicate that the degradation process begins with carbonization of the plastic encapsulation meterial on the diode surface, which leads to the formation of a conductve path across the LED and subsequently to the destruction of the diode itself.