On the origin of efficiency roll-off in InGaN-based light-emitting diodes

The external quantum efficiency (EQE) of AlInGaN-based light-emitting diodes (LEDs) on sapphire and bulk GaN substrates was measured over a wide range of pulsed currents with small duty cycles. The current dependence of the EQE appeared to be a strong function of the In content but nearly independent of the dislocation density in the active region. The EQE of the InGaN LEDs peaked at very low currents and decreased dramatically at high currents, whereas the AlGaN UV LED attained a saturated EQE as current increases. In contrast to minimal peak shift in the UV LED, a monotonic current-induced blueshift of the peak energy was seen up to 1 kA/cm2 for the InGaN blue and green LEDs. These results suggest that the capture of delocalized carriers by nonradiative recombination centers such as misfit defects is the major nonthermal mechanism of efficiency roll-off in InGaN LEDs.