Mg-doped GaN with cubic structure have been grown by molecular beam epitaxy on sapphire substrate. Temperature-dependent photoluminescence of heavily Mg-doped GaN have been investigated in order to study the properities of donor-acceptor pair recombination. We have found unusual temperature dependent behaviors of donor-acceptor pair recombination in heavily Mg-doped GaN. The photoluminescence intensity of donor-acceptor pair recombination decreases below 35K and then increases as the temperature increases up to 100K. This behavior may be explained by employing three energy level system

e.g. shallow donor level

shallow acceptor level and hole trap level. The main transition processes and their dynamic processes of non equilibrum holes

which bumped by excited laser

have been studied. The holes are caught in the hole traps and they subsequently transfer from the traps to shallow acceptors by tunneling

where recombination with electrons takes place. The theoretical calculations are in accordance with the experiment results. The PL intensity of donor-acceptor recombination in heavily Mg-doped GaN is determined by the effects of hole trap and tunneling.