Degradation of blue AlGaN/InGaN/GaN LEDs subjected to high current pulses

Abstract

-Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LEDs based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries[l]. The Nichia diodes are 100 times brighter than the previously available S i c blue LEDs. Group-111 nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LEDs have been reported. Our study, reported in this paper, focuses on the performance of GaN LEDs under high electrical stress conditions. Our observations indicate that, in spite of a high defect density, which normally would have be fatal to other III-V devices, defects in group-111 nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-III nitrides grown on sapphire.

Life tests and failure mechanisms of GaN/AlGaN/InGaN light-emitting diodes

“…These results indicate that Nichia devices enjoy a remarkable longevity in spite of their high density of defects [12]. Only one of the older technology, double heterostructure Nichia LEDs showed a greater than 50% light output degradation after 1200 hours.…”

“…We also know from our earlier work [12] that the band-to-band emission component does increase significantly with forward bias indicating that the newer generation LEDs should have a long lifetime at currents less than the 20 mA cw limit in the data sheet, but may show significant degradation by this mechanism at elevated currents.…”