Computational study of native defects and defect migration in wurtzite AlN: an atomistic approach

We derive an empirical, lattice energy consistent interatomic force field model for wurtzite AlN to predict consistently a wide range of physical and defect properties. Using Mott-Littleton techniques, we calculate formation energies of vacancies and interstitials, which show good agreement with previous ab initio calculations at the edge of the band gap. A novel N3- interstitialcy configuration is proposed to be of lower energy than the octahedral-channel-centred counterpart. With the assistance of the QM/MM method, our potential can predict a VBM level (-7.35 eV) comparable to previous experimental measurements. We further investigate the migration mechanisms and energy barriers of the main intrinsic defects. For the vacancy migration, the axial migration barrier is found to be lower than the basal migration barrier, in contrast to previous calculations. Two interstitialcy migration mechanisms for the interstitial defects are proposed, the "knock-out" mechanism for Al interstitial and the "hand-over" mechanism for N interstitialcy defects. The new force field model proposed here demonstrates that the empirical two-body interatomic potential is still effective for the study of defect properties, electronic states, and other extended systems of III/V semiconductors and further can be employed with QM/MM embedded techniques.