The preparation of GaSb substrates for epitaxial growth of GaSb and GaInAsSb is reported. The effects of several wet chemical etchants and ambient atmosphere during substrate heating on surface morphology and interfacial impurities were investigated. Based on surface roughness and interfacial contamination, which were determined by atomic force microscopy and by secondary ion mass spectroscopy, respectively, the most suitable etchant is one that does not attack GaSb and preferentially removes only the oxide layer. Characterization of metastable GaInAsSb epilayers shows that the starting surface roughness can impact the extent of phase separation, and higher material quality is achieved for a smoother GaSb substrate surface. These results indicate that morphological undulations associated with surface roughness can enhance alloy decomposition, and are detrimental for growth of metastable alloys. (C) 2003 Elsevier B.V. All rights reserved.