SCANNING-TUNNELING-MICROSCOPY OF INAS GASB SUPERLATTICES - SUBBANDS, INTERFACE ROUGHNESS, AND INTERFACE ASYMMETRY/

Scanning tunneling microscopy and spectroscopy is used to characterize InAs/GaSb superlattices, grown by molecular-beam epitaxy. Roughness a t the interfaces between InAs and GaSb layers is directly observed in the images, and a quantitative spectrum of this roughness is obtained. Electron subbands in the InAs layers are resolved in spectroscopy. As ymmetry between the interfaces of InAs grown on GaSb compared with GaS b grown on InAs is seen in voltage-dependent imaging. Detailed spectro scopic study of the interfaces reveals some subtle differences between the two in terms of their valence-band onsets and conduction-band sta te density. These differences are interpreted in a model in which the GaSb on InAs interface has an abrupt InSb-like structure, but at the I nAs on GaSb interface some Sb grading occurs into the InAs overlayer.