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 (100)
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.