Effects of As2 versus As4 on InAs/GaSb heterostructures: As-for-Sb exchange and film stability

We have used cross-sectional scanning tunneling microscopy and x-ray diffraction to characterize and compare the effects of ${\mathrm{As}}_{\mathrm{2}}$ versus ${\mathrm{As}}_{\mathrm{4}}$ on the growth of InAs/GaSb heterostructures by molecular beam epitaxy. When GaSb surfaces are exposed to an ${\mathrm{As}}_{\mathrm{2}}$ flux, the As exchanges with the surface Sb in an anion exchange reaction that creates layers of GaAs. In contrast, when GaSb surfaces are exposed to ${\mathrm{As}}_{\mathrm{4}}$ fluxes, there is no evidence of the As-for-Sb exchange reaction. When comparing the use of ${\mathrm{As}}_{\mathrm{2}}$ and ${\mathrm{As}}_{\mathrm{4}}$ in periodic InAs/GaSb superlattices, the differences in the As incorporation rate into GaSb is further evident in x-ray diffraction spectra as a shift in the average lattice constant of the epilayer due to GaAs bond formation. Although inhibiting the exchange reaction would be useful in the minimization of the cross incorporation of As in the GaSb layers, the growth of InAs/GaSb heterostructures using ${\mathrm{As}}_{\mathrm{4}}$ can be complicated by the introduction of film instabilities that have not been observed in growths using ${\mathrm{As}}_{\mathrm{2}}.$