First-principles calculations were used to investigate the structures and properties of screw and edge dislocations. The atoms at the core of the full core screw dislocation had heavily strained bonds which led to deep gap states. Removing the first shell of Ga and N atoms gave a screw dislocation with a small open core which consisted of {10•0}-type surfaces. Open-core screw dislocations therefore introduced only shallow gap states. In the same way, it was found that the core of the threading edge dislocation was reconstructed without any deep states. The interaction of O with the cores of open-core screw and edge dislocations was considered, and it was found that the impurity had a strong tendency to be bound by Ga vacancies; thus leading to 3 types of defect being trapped in the strain field. It was suggested that the most stable defect led to the poisoning of growth centres on the walls of nanopipes.

Interaction of Oxygen with Threading Dislocations in GaN. R.Jones, J.Elsner, M.Haugk, R.Gutierrez, T.Frauenheim, M.I.Heggie, S.Oberg, P.R.Briddon: Physica Status Solidi A, 1999, 171[1], 167-73