Fundamental reactions controlling anion exchange during mixed anion heterojunction formation: Chemistry of As-for-Sb and Sb-for-As exchange reactions

As-for-Sb and Sb-for-As anion exchange reactions have been investigated by the exposure of GaSb surfaces to As-2 and As-4 species and by the exposure of GaAs to Sb-2, respectively. The effect of surface temperature, anion soak time, and anion species (either As-2 or As-4) on the chemistry governing the anion exchange reactions during GaAsySb1-y/GaSb and GaSbyAs1-y/GaAs heterostructure formation by molecular beam epitaxy is examined. It is found that when GaSb surfaces are exposed to arsenic, the anion exchange reaction competes with the formation of isoelectronic compounds, AsSby, which form clusters precipitating in the GaAsySb1-y/GaSb heterostructures. The relative amount of GaAs and AsSby depends on the surface temperature, the As soak time, and on the As species, i.e., As-2 or As-4. We observe specific process conditions that minimize AsSby formation, yielding more abrupt heterojunction interfaces. In the case of the Sb-2/GaAs system, the Sb-for-As anion exchange does not occur to a significant degree, but surface segregation of antimony is found. A chemical model for the As-for-Sb anion exchange reaction is proposed