Electronic versus geometric contrast in cross-sectional STM images of III-V semiconductor heterostructures

We report first-principles calculations of the electronic and geometric structure of the (110) cross-sectional surfaces on InAs/GaSb superlattices, and compare the results with scanning tunneling microscopy images of filled electronic states. In both the predicted and measured images the InAs surfaces appear lower than GaSb, a height difference we show is caused primarily by differences in the electronic structure of the two materials. In contrast, local variations in the apparent height of surface atoms at InSb- or GaAs-like interfaces arise primarily from geometric distortions associated with local differences in bond length. Our calculated energies for atomic intermixing indicate that anion exchanges are exothermic at GaAs interfaces but endothermic at InSb interfaces. This difference may explain why GaAs interfaces are typically more disordered than InSb interfaces in these heterostructures.