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.

Electrical Properties of Nichia AlGaN/InGaN/GaN Blue LEDs in a Wide Current/Temperature Range

“…[3], the electromigration of contact metals may be responsible for such phenomenon. The micro-shunts cause the luminescence degradation by creating parallel leakage paths, which decreases the fraction of the uniform junction current in the total current of the diode.…”

“…Some devices became heavily degraded (great loss of light emission efficiency) under forward-bias overload (at current pulse amplitudes significantly larger than 1.5 A). Failure analysis was performed on these devices in order to identify defects responsible for the degradation [3].…”