Free exciton emission in GaN

We present a detailed study of the free exciton emission in GaN. Photoluminescence and photoluminescence excitation techniques are employed to show the dominant role of exciton-phonon interaction in the creation of the free exciton states and the free exciton emission cascade in GaN. Up to six longitudinal optical (LO) phonon replicas are observed in both photoluminescence and photoluminescence excitation spectra. From an analysis of the free exciton line shape we are able to conclude that free exciton emission and the interaction of free excitons with LO phonons have to be described within the framework of the momentum conservation law. The exciton kinetic energy distribution is found to be a Maxwellian one having the temperature of the lattice. This suggests an enhanced rate of free exciton scattering on the acoustic phonons, in contrast to other wurzite-type semiconductors. © 1996 The American Physical Society.