We apply positron annihilation spectroscopy to identify $V_{\mathrm{N}}\mathrm{\text{−}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ complexes as native defects in Mg-doped GaN. These defects dissociate in postgrowth annealings at $500–800°\mathrm{C}$. We conclude that $V_{\mathrm{N}}\mathrm{\text{−}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ complexes contribute to the electrical compensation of Mg as well as the activation of $p$-type conductivity in the annealing. The observation of $V_{\mathrm{N}}\mathrm{\text{−}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ complexes confirms that vacancy defects in either the N or Ga sublattice are abundant in GaN at any position of the Fermi level during growth, as predicted previously by theoretical calculations.

• Received 20 December 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.137402