Temporally and spatially resolved spectroscopy of GaN

We report temporally and spatially resolved photoluminescence (PL) measurem ents on a high-quality single crystal GaN film grown on GaN substrates by m etalorganic chemical vapour deposition (MOCVD). The PL decay times for the free A-excitons and the donor-bound excitons obtained under low excitation density (100 W/cm(2)) at liquid helium temperature were about 60 and 250 ps , respectively. Measurements of the PL under higher excitation densities (u p to 9 kW/cm(2)) show that the recombination rates of both free and bound e xcitons are slower, this observation can be explained by detrapping of dono r bound excitons. In spatially resolved measurements, a slight time delay o f the free exciton photoluminescence for distant points has been observed. Numerical modeling shows that this delay can be explained by an exciton-pol ariton transport with a diffusion constant of approximately 100 cm(2)/s.