In0.8Al0.2Sb/InSb layers were grown under various growth temperature and V/III flux ratio conditions on semi-insulating (001)oriented GaAs substrates by molecular beam epitaxy. The crystalline qualities of In0.8Al0.2Sb/InSb layers were improved by decreasing the V/III flux ratio at a fixed temperature (380 degrees C) and increasing the growth temperature of the fixed V/III ratio (6). Dislocations were only observed in the In0.8Al0.2Sb/InSb layers grown at the optimal condition. On the other hand, many planar defects, including microtwins, were observed when the In0.8Al0.2Sb/InSb layers were grown in the Sb-rich condition. Specifically, V-shaped defects drawn boundaries in the microtwins were observed in the In0.8Al0.2Sb/InSb layer. (c) 2006 Elsevier B.V. All rights reserved.