The diffusion of relevant native point defects in wurtzite crystals was investigated by using first-principles density-functional pseudopotential calculations. A re-examination of the ground state of the defects, using a higher level of convergence than was previously used, yielded results which were in good agreement with earlier published results. The Ga interstitials were stable at the octahedral interstitial site, and could occur in 1+, 2+ (metastable) or 3+ charge states. They migrated via an interstitialcy mechanism with an unexpectedly low barrier of 0.9eV. This was consistent with the annealing of the L5 signal in electron paramagnetic resonance experiments. For the N interstitial, the ground-state configuration was a split interstitial which occurred in charge states ranging from 1– to 3+. Migration also proceeded via an interstitialcy mechanism, with barriers of 2.4eV or lower; depending upon the charge state. The N vacancy had 2 stable charge states: 1+ and 3+. The migration barrier for VN+ was high (4.3eV), while the migration barrier for VN3+ was significantly lower, at 2.6eV; consistent with recent positron annihilation experiments. The Ga vacancy could occur in charge states of 0, 1–, 2– or 3–, and migrated with a barrier of 1.9eV. For all of these defects, the lowest-energy migration path resulted in motion both parallel and perpendicular to the c-axis. No anisotropy in the diffusion was therefore expected to be observable.

Diffusivity of Native Defects in GaN. S.Limpijumnong, C.G.Van de Walle: Physical Review B, 2004, 69[3], 035207