Annealing of ion-implanted GaN

$^{111m}$Cd and $^{112}$Cd ions have been implanted into GaN. With photoluminescence spectroscopy and perturbed $\gamma-\gamma$-angular correlation spectroscopy (PAC) the reduction of implantation damage and the optical activation of the implants have been observed as a function of annealing temperature using different annealing methods. The use of N$_{2}$ or NH$_{3}$ atmosphere during annealing allows temperatures up to 1323k and 1373 K, respectively, but above 1200 K a strong loss of Cd from the GaN has been observed. Annealing GaN together with elementary Al forms a protective layer on the GaN surface allowing annealing temperatures up to 1570 K for 10 min. (11 refs).