Ab initio studies of atomic-scale defects in GaN and AlN

The plane-wave pseudopotential method is applied to study point-defects and their complexes in GaN and AlN. The calculations reveal a qualitative difference in the donor behavior between the two materials: the oxygen and silicon impurities act as shallow donors in GaN while in AlN they have a deep character, in good agreement with the experimentally measured conductivity. Therefore a DX-behavior is predicted for these donor defects in AlxGa1-xN alloys with sufficient Al concentration. Effective compensation through cation vacancies (V-Ga,V-Al) and related defect complexes is shown to occur in both materials. We present evidence that the broadband luminescence (yellow in GaN and violet in AlN) originates from electronic transitions between the donor and acceptor levels induced by the defects mentioned above.