We present a surface X-ray diffraction and Auger electron spectroscopy investigation of antimony capping layers used to protect indium antimonide and gallium antimonide epilayers. A thermally induced amorphous to polycrystalline structural transition was observed at approximately 190 degrees C for Sb caps on InSb(001) and GaSb(001) substrates. We conclude that 100nm Sb caps deposited at elevated substrate temperature (150-200 degrees C) have superior structural order, and are able to protect III-Sb epilayers from atmospheric contamination for periods of at least a year. (c) 2006 Elsevier B.V. All rights reserved.