We show that thep-type doping ofGa0.5In0.5Pgrown by solid-source molecular beam epitaxy usingCBr4as a carbon source is very strongly dependent upon the phosphorus flux and upon the substrate misorientation from (100). High densities ofA-type steps and low phosphorus flux favor the incorporated carbon acting as ap-type dopant. We demonstrate that with the substrate orientation and phosphorus flux chosen to satisfy these two criteria, doping ofC:Ga0.5In0.5Pinto the mid-1018 holes/cm3range can be achieved for the as-grown material. ©1997 American Institute of Physics.