Mg-doped GaN:: Similar defects in bulk crystals and layers grown on Al2O3 by metal-organic chemical-vapor deposition

Defects were observed in GaN:Mg grown on sapphire substrates using metal-organic chemical-vapor deposition (MOCVD) with Mg-delta doping similar to those previously observed in bulk GaN:Mg grown from Ga solution under high hydrostatic pressure of nitrogen. Pyramidal defects (pinholes) with (<1(1)over bar>00) hexagonal facets on the (0001) base plane and six {11(2) over bar 2} side facets, and defects with a rectangular shape also delineated by planar facets on the basal (0001) planes, were observed for growth with Ga polarity for both of these very different growth methods. The Mg dopant is apparently responsible for their formation since the oxygen concentration in the MOCVD-grown samples was orders of magnitude lower than in the bulk samples. Mg segregation on these planes apparently does not allow uniform continuous growth on these planes leading to these hollow defects. Some defects in the heterolayers also develop into longer nanotubes elongated along the c axis. Change of polarity from Ga to N followed by a change back to Ga polarity also resulted in formation of planar defects previously observed in bulk samples for growth with N polarity. (C) 1999 American Institute of Physics. [S0003-6951(99)01850-1].