Atomic and electronic structures of full-core threading screw dislocations in wurtzite GaN were studied by using a self-consistent density-functional tight-binding calculation. It was shown that the atoms were severely strained in an hexagonal atomic core, and an extra charge transfer of 0.12e occurred at the core atoms from Ga to N; in addition to the typical charge transfer of 0.56e for bulk GaN. Filled and unfilled gap states were found to be spread over the entire band gap. The p states of the core N-atom contributed mainly to the tail states of the valence and conduction bands, whereas the deep levels were heavily localized at the Ga and N core atoms. The coexistence of acceptor and donor gap states in the vicinity of the screw dislocations could be an origin of the leakage currents observed in GaN-based devices.

Local Electronic Structure of Threading Screw Dislocation in Wurtzite GaN. I.Belabbas, M.A.Belkhir, Y.H.Lee, J.Chen, A.Béré, P.Ruterana, G.Nouet: Computational Materials Science, 2006, 37[3], 410-6