Vacancy Defects as Compensating Centers in Mg-Doped GaN

We apply positron annihilation spectroscopy to identify ${V}_{\mathrm{N}}\mathrm{\text{\ensuremath{-}}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ complexes as native defects in Mg-doped GaN. These defects dissociate in postgrowth annealings at $500\char21{}800\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. We conclude that ${V}_{\mathrm{N}}\mathrm{\text{\ensuremath{-}}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ complexes contribute to the electrical compensation of Mg as well as the activation of $p$-type conductivity in the annealing. The observation of ${V}_{\mathrm{N}}\mathrm{\text{\ensuremath{-}}}{\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ 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.