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

We performed a degradation study of high-brightness Nichia single-quantum w ell AlGaN/InGaN/GaN green light-emitting diodes (LEDs). The devices were su bjected to high current electrical stress with current pulse amplitudes bet ween 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 ampl itude was increased above 6 A, a fast (about 1 s) degradation occurred, wit h a visible discharge between the p- and n-type electrodes. Subsequent fail ure analysis revealed severe damage to the metal contacts, which lead to th e formation of shorts in the surface plane of the diode. For currents small er 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 degradati on occurred between 24 and 100 h which was similar to the rapid degradation observed at higher currents. The failure analysis results indicate that th e degradation process begins with carbonization of the plastic encapsulatio n material on the diode surface, which leads to the formation of a conducti ve path across the LED and subsequently to the destruction of the diode its elf. (C) 1999 Elsevier Science Ltd. All rights reserved.