Cross-sectional scanning tunneling microscopy of InAsSb/InAsP superlattices

Cross-sectional scanning tunneling microscopy (STM) has been used to characterize compositional structures in InAs0.87Sb0.13/InAs0.73P0.27 and InAs0.83Sb0.17/InAs0.60P0.40 strained-layer superlattice structures grown by metal-organic chemical vapor deposition. High-resolution STM images of the (110) cross section reveal compositional features within both the InAsxSb1−x and InAsyP1−y alloy layers oriented along the [1̄12] and [11̄2] directions—the same as those in which features would be observed for CuPt–B type ordered alloys. Typically one variant dominates in a given area, although occasionally the coexistence of both variants is observed. Furthermore, such features in the alloy layers appear to be correlated across heterojunction interfaces in a manner that provides support for III–V alloy ordering models which suggest that compositional order can arise from strain-induced order near the surface of an epitaxially growing crystal. Finally, atomically resolved (11̄0) images obtained from the InAs0.87Sb0.13/InAs0.73P0.27 sample reveal compositional features in the [112] and [1̄1̄2] directions, i.e., those in which features would be observed for CuPt–A type ordering.