Short term instabilities of InGaN/GaN light-emitting diodes by capacitance-voltage characteristics and junction spectroscopy

We present a combined capacitance-voltage, Deep Level Transient Spectroscopy (DLTS) and electroluminescence (EL) study of short-term instabilities of InGaN/GaN LEDs submitted to forward current aging tests at room temperature. In the early stages of the aging tests at low forward current levels (15 and 20 mA), LEDs present a decrease in optical emission, which stabilizes within the first 50 hours and never exceeds 20% (measured at an output current of 1 mA after stressing the LEDs for 50 hours with 15 mA stress). The spectral distribution of the EL intensity does not change with stress, while C-V profiles detect changes consisting in apparent doping and/or charge concentration increase within quantum wells. This increase is correlated with the decrease in optical power. DLTS has been carried out to clarify the DC aging induced generation/modification of the energy levels present in the devices. Remarkable changes occur after the stress, which can be related to the doping/ charge variation and thus to the efficiency loss