M-plane GaN thin films grown on γ-LiAlO2 substrate were investigated at different temperatures by photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. The origin of two distinct emissions, P1 and P2 observed in the PL spectra were established by analyzing their PL and TRPL properties at different temperatures. The P1 emission is attributed to the excitons bound to the stacking faults (SFs). The P2 shows an anomalous “S-shaped” emission shift with increasing temperature (T), and the associated mechanism is discussed. The radiative life time ‘τr’ for P2 emission exhibits the T 3/2 dependence at higher temperatures and deviates at lower temperatures whereas the radiative life time ‘τr’ for P1 emission does not show the T 3/2 dependence with temperature. The polarization-dependent PL study reveals that P2 emission involves free holes in the transition at room temperature.
