High electron mobility and low defect density InAsSb lattice matched to AlSb has been successfully grown on InP substrates by the gas-source molecular beam epitaxy using an AlAsSb/AlSb composite buffer layer structure. The common antimony anion of AlAsSb, AlSb, and InAsSb is believed to effectively improve the film quality of InAsSb and AlSb by providing a surfactant effect. With this composite buffer layer structure, the room temperature electron mobility of InAsSb (lattice matched to AlSb) can reach as high as 18,000 cm(2)/V s. A high electron-mobility transistor based on this heterostructure shows a high g of 350 mS/mm (gate length=6 mu m) indicating the potential for high-speed applications. (C) 2008 Elsevier B.V. All rights reserved.