Temperature dependence of the radiative recombination in GaN

We have studied the radiative recombination from two different type of GaN samples using photoluminescence and time resolved photoluminescence, in the temperature range from 2 K to room temperature. The emission at low temperatures is dominated by the recombination of donor bound excitons, with decay time of about 250 ps. At temperatures from 40 K and up to room temperature the free exciton recombination is dominating. In the bulk sample we observe an increase of the measured decay time at temperatures up to 15 K, interpreted as the presence of a dominating radiative recombination for the free exciton. The decay time of the free exciton at higher temperatures is dominated by non-radiative recombination.