The atomic and electronic structures of a N vacancy in the (3¯7▪0) Σ = 37 (θ = 9.3º) tilt grain boundary in GaN were investigated by density-functional based tight-binding calculations. It was shown that the electronic structure of the N-vacancy was characterised by one fully occupied energy level at E1 = EVB+0.72eV and 2 unoccupied states, each 2-fold degenerate, at E2 = EVB+2.20eV and E3 = EVB+2.43eV. The E2 level might act as a source or a trap for electrons and might contribute to the yellow luminescence.
Atomistic Modelling of Point Defects in  Tilt Boundaries in GaN. A.Béré, J.Chen, G.Nouet, P.Ruterana, J.Koulidiati: Physica Status Solidi C, 2005, 2, 2496-9