In pursuit of p-type doping, we have implanted GaN with Mg ions at 200 and 500keV with the substrate temperature maintained at −150 (cold) or +300°C (hot) during ion irradiation. The samples have been annealed at 1000°C postion implantation. The radiation damage peak position (and its profile), the dopant distribution, and the damage stability during annealing were all shown to be dependent upon the GaN substrate temperature during implantation. The damage peak position in the solid was reduced for cold implantation. The dopant distribution in the solid depends upon the implant temperature and in agreement with the damage measurements, the Mg range is shallower in GaN for cold implants when compared to hot implants. The trends observed suggest that the dynamic defect annealing rate during irradiation is reduced for cold implantation, and the subsequent increase in the damage level (scattering …