Time-resolved photoluminescence spectroscopy of individual GaN nanowires

We investigate individual and ensembles of free-standing GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy using time-resolved photoluminescence (TRPL) spectroscopy. The PL transients of individual NWs always show a single exponential decay, independent of the excitation density. However, different NWs exhibit different decay times ranging from about 50 to 400 ps. In contrast, the PL transients of the NW ensemble always exhibit a nonexponential decay even at low excitation densities. We conclude that this nonexponential PL decay of the NW ensemble is a superposition of the different decay times of the different individual NWs in the ensemble. The origin of these different decay times is attributed to the impact of surface recombination.