Interpreting interfacial structure in cross-sectional STM images of III–V semiconductor heterostructures

Using model GaSb–InAs heterostructures, we have systematically examined how cross-sectional scanning tunneling microscopy (XSTM) can be used for the study of III–V heterostructure interfaces. The interpretation of interfacial structure in XSTM images is impeded by the fact that only every other III or V plane as grown on the (001) substrate is seen in each image. We show how this structural artifact affects spectral analyses of interfacial roughness, preventing an accurate analysis when interfaces are just a few layers wide. Additional complications arise due to the inequivalence of the (110) and (1̄10) cleavage surfaces and the dependence of interfacial bond orientation on growth order. By taking advantage of the different bond orientations on the two cleavage surfaces, we demonstrate that the contrast observed at the interfacial layers in this system is caused primarily by the geometry of the interfacial bonds, not electronic structure differences. Finally, we illustrate how careful design of model heterostructures can be used to circumvent many limitations of XSTM, and thereby allow one to obtain detailed atomic-scale information about all the growth layers in the structure.