Carrier dynamics and efficiency droop in AlGaN epilayers with different Al content

Abstract

AbstractCarrier dynamics and emission efficiency droop in AlGaN epilayers containing different Al content were studied under pulsed (30 ps) and quasi‐steady‐state photoexcitation. Samples with Al content ranging from 17% to 50% but having similar carrier lifetimes (50‐80 ps) were selected for the study. Considerable heating of nonequilibrium carriers at room temperature was observed. Carrier redistribution down to deeper localized states is demonstrated. It is shown that the temperature decay is faster than the decay of localized carriers, which determine the photoluminescence decay kinetics at later stages of the decay. The efficiency droop onsets at lower excitation power densities in the samples with higher Al content presumably having higher density of nonradiative recombination centers and higher density of localized states. The results are in favour of the assumption that the droop in these epilayers is caused by saturation of the localized states and hopping of less localized carriers to the centers of nonradiative recombination. The effect might be enhanced by carrier heating (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)