The homogeneity and luminescence of undoped bulk material was studied by means of cathodoluminescence scanning electron microscopy. The resultant images revealed a non-uniform distribution of native defects in wafers which were prepared from as-grown single crystals. Post-growth annealing in vacuum, and Ga or Sb atmospheres, was used to obtain more accurate information concerning the defect structure. In general, annealing produced an homogeneous distribution of impurities throughout the wafers. The cathodoluminescence spectra showed that a luminescence band (centered at 0.756eV) was enhanced by annealing in a Ga atmosphere. This suggested that Ga atoms played an important role in the formation of this acceptor center. The 0.756eV peak was attributed to a transition from a conduction band to an acceptor center that comprised GaSb or a related complex. Localized crystallization at the sub-grain boundaries appeared to occur upon annealing in a Ga atmosphere.

B.Méndez, P.S.Dutta, J.Piqueras, E.Dieguez: Applied Physics Letters, 1995, 67[18], 2648-50