Effect of temperature on longitudinal optical phonon-assisted exciton luminescence in heteroepitaxial GaN layer

First-order and second-order longitudinal optical (LO) phonon-assisted luminescence lines of neutral donor-bound excitons and free excitons in heteroepitaxial GaN film have been investigated in temperature range from 3.5 to 50 K. The energy spacing between the exciton resonant lines and their corresponding LO phonon replicas is found to be strong temperature dependent. Permogorov’s theory on LO phonon-assisted luminescence of free excitons could be employed to explain the main experiments. It is also found that the interaction strength of the free exciton with LO phonon is stronger than that of the bound exciton with LO phonon.