Behavior of 2.8- and 3.2-eV photoluminescence bands in Mg-doped GaN at different temperatures and excitation densities

The blue and ultraviolet photoluminescence bands in Mg-doped GaN have been investigated over a wide range of temperatures and excitation intensities. Redshifts of the bands were observed with increasing temperature. The bands underwent a blueshift with increased excitation density. The observed shifts of the 3.2 eV band are explained by a potential fluctuation model for a compensated semiconductor. In contrast, the shifts of the 2.8 eV band are essentially related to saturation of luminescence from distant donor-acceptor pairs responsible for this emission. Thermal quenching of the 2.8 eV luminescence band was observed at high temperatures with an activation energy of 0.3–0.4 eV. It is attributed to thermal release of trapped electrons from a deep donor state.