The InAs/GaAsSb material system is a promising medium for the implementation of a quantum dot solar cell due to a favorable valence band alignment. The quantum dot solar cell requires a highly dense, highly ordered array of quantum dots for overlap of wave functions to form a band in the band gap of the host material. Since the GaAsSb barriers are a III-V-V ternary the alloy composition is particularly sensitive to variations in temperature. We have studied the variation in Sb content for thin layers of GaAsSb in GaAs for various fluxes of Sb. The purpose was to be able to predict the required Sb flux at a particular temperature to obtain a desired Sb composition. The target Sb composition for this study was 12% with the composition obtained confirmed by x-ray diffraction. By also studying the reciprocal space maps of the 12% samples, it is inferred that the composition can be maintained for a large temperature range. The implications of these results for the growth of InAs quantum dots on GaAsSb barriers are briefly discussed. (C) 2008 American Vacuum Society.