Phonon-assisted photoluminescence in wurtzite GaN epilayer

Temperature-dependent photoluminescence of a wurtzite GaN epilayer was measured in the range of 4 to 300 K. At low temperature, the neutral-donor bound exciton emission dominates the spectra, while with increasing temperature, free exciton emissions grow rapidly and finally become the dominant lines. The contribution of the exciton-phonon interaction to the exciton linewidth was studied. Beside the exciton emissions, LO-phonon-assisted photoluminescence associated with both the bound exciton and the free exciton was observed. The temperature dependence of LO-phonon-assisted emissions can be well explained by the phonon-assisted free exciton emission theory established for Il-VI compound semiconductors by Permogorov. In particular, the study of the 2LO phonon replica can provide information on the temperature dependence of the concentration and recombination lifetime of free excitons in GaN.