Buffer layers of GaAs1−xSbx were grown on an InP substrate starting at x=0.49 (lattice matched to InP) and increasing x in steps of 0.03–1.0 (GaSb), followed by a 0.5μm thick GaSb metamorphic layer. A 10nm thick InAs quantum well was grown on top and capped with a 100nm GaSb. All layers were grown using gas source molecular beam epitaxy by reducing the As flux in small steps while keeping the Sb flux fixed. The substrate temperature during growth was ∼490°C. High-Resolution x-ray diffraction analysis showed that the metamorphic layer was almost fully relaxed. Cross-sectional transmission electron microscopy images show that a postgrowth anneal at 600°C for 30s successfully reduces the number of dislocations threading through the metamorphic layer. Hence the top layer can be used satisfactorily as a pseudosubstrate for subsequent layer growths assuming a GaSb lattice constant.