Investigation of native defects and impurities in X-N (X = Al, Ga, In)

Defects have a decisive influence on the performance of III-V devices. In this paper, we systematically investigated the native point defects and impurities in group III nitride semiconductors X-N (X = Al, Ga, In) using density functional theory calculations. We studied the geometric and mechanical properties of these nitrides first, the bulk moduli were calculated and analyzed. Then by considering both anion-rich and cation-rich conditions, formation energies and corresponding thermodynamic charge transition levels of these defects were presented. Specifically, our results indicate the elastic stiffness is reduced with the introduction of defects. The nitrogen antisite, the magnesium-nitrogen substitution, and oxygen-X (X = Al, Ga, In) substitution have the most significant decrease in the bulk moduli, which are consistent with their formation energies. For native defects, the nitrogen vacancies are the most stable ones, but still are energetically unfavorable for the experimentally detected n-type conductivity of these nitrides. Interstitials and antisite defects are uneasy to be formed in n-type situations, but they could act as acceptors in p-type nitrides. For magnesium and oxygen impurities, our results have shown that the magnesium usually acts as p-type dopants, and the incorporated oxygen impurities could be the reason for the experimentally detected n-type conductivity. By studying and understanding the properties of these defects and impurities, we address new possibilities for designing and performance improvement of the group III nitride devices.