The surfactant effects of antimony enhances the carbon (C) dopant incorporation into substitutional sites in GaAsSb:C grown by solid source molecular beam epitaxy. A hole mobility greater than 50 cm(2)/V S for doping levels over 9 x 10(19) cm(-3) was achieved using a solid CBr4 source. 5.4 x 10(-8) Torr of carbon flux giving a hole concentration of similar to7 x 10(19) cm(-3) in GaAs, reaches beyond 9 x 10(19) cm(-3) with the addition of similar to4 x 10(-8) Torr of Sb. With increasing Sb doping concentration, the rate of C incorporation into substitutional sites increases, the photoluminescence characteristics are improved and the net hole concentration increases due to the reduction of interstitial carbon. However when Sb doping is increased further, gallium vacancies and Ga-Sb antisites could create point defects, causing epitaxial degradation. (C) 2004 Elsevier B.V. All rights reserved.