Radiative and Nonradiative Exciton Lifetimes in GaN Grown by Molecular Beam Epitaxy

GaN epilayers grown by molecular-beam epitaxy (MBE) have been studied by temperature dependent time-resolved photoluminescence (PL). The PL decay times for free excitons and donor-bound excitons as well as the quantum efficiency have been measured for different temperatures. Radiative and nonradiative lifetimes have been evaluated from experimental values for the quantum efficiency and the PL decay time, assuming fully radiative processes at 2 K. The so obtained temperature dependence for the radiative lifetime cannot be described by a simple T^3/2 law for the whole temperature range. The temperature behavior of radiative lifetimes suggests the presence of a strong nonradiative recombination channel even at very low temperatures.