Defects may cause compensation or act as recombination centers in Mg-doped GaN. Using hybrid functional calculations, an investigation was made of the effects of nitrogen vacancies (VN) and Mg-vacancy complexes (MgGa-VN) on the electrical and optical properties of GaN. It was found that MgGa-VN were compensating centers in p-type but electrically inactive in n-type GaN. They give rise to a broad emission at 1.8eV, explaining the red luminescence that was frequently observed in Mg-doped GaN, regardless of the Fermi level. Nitrogen vacancies were also compensating centers in p-type GaN and likely contribute to the yellow luminescence that was observed in Mg-doped GaN.

Role of Nitrogen Vacancies in the Luminescence of Mg-Doped GaN. Q.Yan, A.Janotti, M.Scheffler, C.G.Van de Walle: Applied Physics Letters, 2012, 100[14], 142110