The effects of antimony incorporation and a convex compositional step-gradient on the surface morphology, defect generation, and defect propagation properties of InAsyP1-y metamorphic buffer layers (MBLs) were investigated. The incorporation of Sb reduces the root-mean-square (RMS) of the surface roughness, and complete elimination of the arsenic from the MBL (i.e. InPzSb1-z) leads to a reduction of RMS values of the surface roughness from 16 nm (InAsyP1-y) to 3.4 nm (InPzSb1-z), without noticeably altering the defect density in the upper layers of the MBL. InP1-xSbx layers grown on an InPzSb1-z MBL have reduced hillock formation and exhibit energy bandgaps within 8% of that expected from theory. Published by Elsevier B.V.