Structural and electronic properties of line defects in GaN

We present density-functional theory based studies for several types of lin e defects in both hexagonal and cubic GaN. (10-10) type surfaces play an im portant role in hexagonal GaN since similar configurations occur at open-co re screw dislocations and nanopipes as well as at the core of threading edg e dislocations. Except for full-core screw dislocations which possess heavi ly strained bonds all investigated stoichiometric extended defects in hexag onal GaN do not induce deep acceptor states in the band-gap and thus cannot be responsible for the yellow luminescence. However, electrically active p oint defects in particular gallium vacancies and oxygen related defect comp lexes are found to be trapped at the stress field of the dislocations. Prel iminary calculations for cubic GaN find the ideal stoichiometric 60 degrees -dislocations to be electrically active. As in hexagonal material, vacanci es and impurities like oxygen are likely to be trapped at the dislocation c ore.