The properties of defect complexes consisting of a N vacancy with a substitutional Be or Mg atom on neighboring lattice sites in hexagonal GaN were calculated by using the AIMPRO local-density-functional theory method. Both types of defects VN-BeGa and VN-MgGa were bound with respect to their isolated constituents. They did not appear to have any electronic levels in the band-gap, and were expected to be neutral defects. Important structural differences were found. In its minimum energy configuration, the Be atom in the VN-BeGa complex lies nearly in the same plane as the three equivalent N atoms nearest to it. Thus, it had shorter Be-N bonds than the Ga-N distance in the bulk crystal, while the Mg atom in the VN-MgGa complex occupies a position closer the lattice site of the Ga atom it replaces. Hence, the VN-BeGa complex had a larger open volume than the VN-MgGa complex. This was consistent with positron annihilation experiments. The frequency of the highest local vibrational mode of the VN-BeGa center was calculated to be within 3–4% of an infrared absorption line detected in Be-doped GaN.

Calculated Properties of Nitrogen-Vacancy Complexes in Beryllium- and Magnesium-Doped GaN. C.D.Latham, R.Jones, S.Öberg, R.M.Nieminen, P.R.Briddon: Physical Review B, 2003, 68[20], 205209 (5pp)