A scanning tunneling microscopy study of atomic-scale clustering in InAsP/InP heterostructures

Abstract
We have used cross-sectional scanning tunneling microscopy to perform atomic-scale characterization of InAs0.35P0.65/InP strained-layer multiple-quantum-well structures grown by gas-source molecular-beam epitaxy. High-resolution (110) cross-sectional images reveal nanoscale clustering of As and P in the InAsxP1−x alloy layers. Boundaries between As-rich and P-rich regions in the alloy layers appear to be preferentially oriented along the [1̄12] and [11̄2] directions in the (110) plane, suggesting that boundaries between As-rich and P-rich clusters tend to form within {111} planes in the lattice. The nanoscale compositional variations within the InAsxP1−x alloy layers lead to an asymmetry in interface quality in the (110) cross section, with the InAsxP1−x-on-InP interfaces being much smoother and more abrupt than the InP-on-InAsxP1−x interfaces. Analysis of (11̄0) cross-sectional images suggests that the clusters formed within the InAsxP1−x alloy are elongated along the [110] direction in the crystal.