COMPOSITIONAL MAPPING OF GASB WAFERS FROM AS-GROWN CRYSTALS AND AFTERPOSTGROWTH ANNEALING TREATMENTS

Spatial compositional analysis has been carried out on single and poly crystal wafers of GaSb grown from stoichiometric and non-stoichiometri c melts. In crystals grown from stoichiometric melt, the ratio of Ga t o Sb is slightly more and remains uniform throughout. At the grain bou ndaries in polycrystals, the Sb content is more than in the other regi ons of the crystal. Crystals grown from either Ga- or Sb-rich melts ex hibit inclusions of the excess component. Post-growth annealing treatm ents in vacuum and Ga-rich atmospheres have been performed. Heat treat ments in vacuum atmosphere produce very little effect on the local com position of the crystal. On the other hand, localized crystallization at grain boundaries and inclusions takes place in the presence of exce ss gallium. It has been shown that annealing treatments in Ga ambient can produce defect-free wafers with extremely homogeneous composition. It is concluded that the excess Sb which is liberated from the crysta l during growth resides at the grain boundaries and other extended def ect centers. The vacant Sb sites are then responsible for the formatio n of the native acceptor centers like V-Ga and Ga-Sb.