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 $As2$ and $As4$ species and by the exposure of GaAs to $Sb2$⁠, respectively. The effect of surface temperature, anion soak time, and anion species (either $As2$ or $As4$⁠) 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., $As2$ or $As4$⁠. We observe specific process conditions that minimize $AsSby$ formation, yielding more abrupt heterojunction interfaces. In the case of the $Sb2∕GaAs$ 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.