The effects of Sb/As soak times, prior to growth of GaAsSb on GaAs were investigated by High Resolution X-Ray Diffraction (HRXRD) and photoluminescence (PL). Multiple quantum well samples with soak times of 0 s, 30 s and 60 s were grown at 500 degrees C with nominally identical Sb and As fluxes. HRXRD results show that a 30 s soak minimizes diffuse scattering seen around superlattice peaks in the reciprocal space maps, an effect attributed to corrugations in the GaAs GaAsSb interface. An inferred band diagram calculated using a four band k.p model and modified taking into account the HRXRD results was used to explain PL spectra taken for each sample at 80 K. It is concluded that an optimum soak time exists for GaASb growth on GaAs, determined by the growth conditions. (C) 2010 Elsevier B.V. All rights reserved.