Changes in the luminescent and electrical properties of InGaN/AlGaN/GaN light-emitting diodes during extended operation

Changes in the luminescence spectra and current-voltage and capacitance-voltage characteristics of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures were investigated as functions of operating time during extended use. Sample blue and green light-emitting diodes with InGaN single quantum-well active layers were examined during operating times of 102−2×103 h at currents up to 80 mA. An increase in the efficiency at the working currents (15 mA) was observed in the first stage of aging (100–800 h) followed by a decrease in the second stage. The greatest changes in the spectra were observed at low currents (<0.15 mA). Studies of the distribution of charged acceptors in the space-charge region showed that their concentration grows in the first stage and falls in the second. Models explaining the two stages of aging are proposed: 1) activation of Mg acceptors as a result of destruction of residual Mg-H complexes, and 2) formation of N donor vacancies. A model of subthreshold defect formation by hot electrons injected into the quantum wells is discussed.