Comparison of electronic and mechanical contrast in scanning tunneling microscopy images of semiconductor heterojunctions

The use of cross-sectional scanning tunneling microscopy (STM) to study strain in semiconductor heterostructures is discussed. In particular, intermixing between constituent heterostructure layers leads to internal strains in the heterostructure, and these strained regions are evident by displacement of the cleavage surface formed in the STM study. A theoretical analysis is made of the magnitude of electronic compared to mechanical contributions to the contrast of STM images, from which it is found that the former are relatively small, on the order of 0.1Å, for typical In_xGa_1−xAs_yP_1−y heterostructures imaged with sufficiently large, positive sample bias.