Abstract
Local density-functional methods are used to examine the behavior of O and O-related defect complexes on the walls of nanopipes in GaN. We find that O has a tendency to segregate to the (101̄0) surface and identify the gallium vacancy surrounded by three oxygen impurities [VGa-(ON)3] to be a particularly stable and electrically inert complex. We suggest that during Stranski-Krastanow growth, when interisland spaces shrink, these defects reach a critical concentration beyond which further growth is prevented and nanopipes are formed. © 1998 American Institute of Physics.