Degradation of GaN-based quantum well light-emitting diodes

Abstract

Electrical and optical properties of AlGaN∕InGaN-based near-ultraviolet (UV) multiquantum well light-emitting diodes have been studied during operation at high junction temperatures. Light output decreased exponentially by 40% in the first 30h after which there was no obvious change. The current-voltage characteristics were almost ideal before degradation, with an ideality factor of approximately 2. During degradation, an additional contribution to the current becomes apparent at voltages of below 2.5V, with a temperature-independent logarithmic slope of the current-voltage characteristic, suggesting an additional transport mechanism by tunneling through defects created during degradation. The evolution of the additional current component corresponded to the two different stages observed in the reduction of the light emission with stress time. Generation of defects with similar effects on forward and reverse bias currents could be correlated with the rapid degradation during the first 30h, but for the second stage, the change in the I-V characteristics did not correlate with the change in light emission. Electroluminescence spectra showed that the emission peaks shifted to slightly lower energies during degradation.