Transition from bound to free excitons observed in deep- ultraviolet photoluminescence of AlN grown by MOCVD

The transition from bound exciton to free exciton and exciton-phonon interaction in an AlN epilayer have been investigated by time resolved deep ultraviolet photoluminescence spectroscopy. Based on the analysis of the energy position (S-shaped dependence with temperature), integrated intensity as well as decay time, the main X peak located at 6.06 eV at 7.7 Kis assigned to originate from radiative recombination of excitons bound to some unintentionally doped Si orOimpurities. While the other two peaks on the lower energy side should be from the bound exciton's phonon replicas. The corresponding small Huang-Rhys factor indicates weak interaction between phonon and bound excitons, in comparison to the case of free exciton, for which our experimental results are in good agreement with the theoretical calculation of the Huang-Rhys factors.