Abstract
We present density-functional theory studies for a variety of surfaces and extended defects in GaN. According to previous theoretical studies {101̄0} type surfaces are electrically inactive. They play an important role in GaN since similar configurations occur at open-core screw dislocations and nanopipes as well as at the core of threading edge-dislocations. Domain boundaries are found to consist of four-fold coordinated atoms and are also found to be electrically inactive. Thus, except for full-core screw dislocations which possess heavily strained bonds all investigated extended defects do not induce deep states into the band-gap. However, electrically active impurities in particular gallium vacancies and oxygen related defect complexes are found to be trapped at the stress field of the extended defects.