Carbon doped GaAsSb samples have been grown by solid source molecular beam epitaxy using carbon tetrabromide as carbon source. A maximal hole concentration of 4.5 x 10(20) cm(-3) has been obtained with a corresponding mobility of 19 cm(2)/V s. For hole concentrations in the 4-8 x 10(19) cm(-3) range, typically used in HBTs, the hole mobility is 45-50cm(2)/V s. We show that 450 degrees C is the optimal growth temperature at which both high hole concentration and mobility are obtained. An InP/GaAsSb/InP DHBT test structure with a 2 x 10(19) cm(-3) carbon doped base has been realised. The current gain beta is about 80 and the emitter-base and base-collector junction ideality factors are 1.15 and 1.05, respectively, indicating good junction properties. (c) 2007 Elsevier B.V. All rights reserved.