A SCANNING-TUNNELING-MICROSCOPY STUDY OF ATOMIC-SCALE CLUSTERING IN INASP INP HETEROSTRUCTURES/

We have used cross-sectional scanning tunneling microscopy to perform atomic-scale characterization of InAs0.35P0.65/InP strained-layer mult iple-quantum-well structures grown by gas-source molecular-beam epitax y. High-resolution (110) cross-sectional images reveal nanoscale clust ering 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 preferential ly oriented along the [<(1)over bar 12>] and [1(1) over bar2$] directi ons 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 l ead to an asymmetry in interface quality in the (110) cross section, w ith the InAsxP1-x-on-InP interfaces being much smoother and more abrup t than the InP-on-InAsxP1-x interfaces. Analysis of (110) cross-sectio nal images suggests that the clusters formed within the InAsxP1-x allo y are elongated along the [110] direction in the crystal. (C) 1998 Ame rican Institute of Physics.