Density-functional theory was used to compute energy-minimum configurations and formation energies of substitutional and interstitial oxygen (O) in wurtzite GaN. The results indicated that O substituted at a N site (ON) acts as a single donor with the ionized state (ON+) being the most stable O state in p-type GaN. In n-type GaN, interstitial O (OI) was predicted to be a double acceptor and O substituted at a Ga site (OGa) was predicted to be a triple acceptor. The formation energies of these two species were comparable to that of ON in n-type GaN and, as such, they should form and compensate the ON donors. The extent of compensation was estimated for both Ga-rich and N-rich conditions with a total O concentration of 1017/cm3. Ga-rich conditions yielded negligible compensation and an ON concentration in excess of 9.9 x 1016/cm3. N-rich conditions yielded a 25% lower ON concentration, due to the increased stability of OI and OGa relative to ON, and moderate compensation. These findings were consistent with experimental results indicating that O acts as a donor in GaN(O). Complexes of ON with the Mg acceptor and OI with the Si donor were examined. Binding energies for charge-conserving reactions were greater than 0.5eV, indicating that these complexes could exist in equilibrium at room temperature. Complexes of ON with the Ga vacancy in n-type GaN were also examined and their binding energies were 1.2 and 1.4eV, indicating that appreciable concentrations could exist in equilibrium even at elevated temperatures.

Substitutional and Interstitial Oxygen in Wurtzite GaN. A.F.Wright: Journal of Applied Physics, 2005, 98[10], 103531