Low-temperature redistribution of non-thermalized carriers and its effect on efficiency droop in AlGaN epilayers

The carrier dynamics in AlGaN epilayers with different degrees of carrier localization were studied using low-temperature photoluminescence spectroscopy at different excitations. We observed a nonmonotonous band peak energy shift with increasing excitation, which is attributed to carrier-density-dependent carrier redistribution within localized states. The carrier redistribution enhances the carrier mobility and increases the nonradiative recombination rate resulting in efficiency droop. These results indicate the significant role of nonradiative recombination even at low temperatures and low carrier densities, despite strong carrier localization. The obtained results are consistent with the excitonic-type nonradiative recombination.