This paper reports the surface morphology of carbon-doped GaAs (GaAs:C) samples grown by solid source molecular beam epitaxy (SSMBE) using carbon tetrabromide (CBR 4 ) as p-dopant source. Sample characterization was carried out using Hall effect, X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. The results show that samples grown at 650°C contain dicarbon defects and the surface morphology is rough. Further experiments on two different sets of GaAs:C samples have shown the absence of bromine-related surface roughening reactions during GaAs:C growth, and the presence of dicarbon defects contribute to the rough surface morphology. It is suggested that the presence of dicarbon defects disrupt the two-dimensional (2-D) step flow growth mode and promote three-dimensional (3-D) growth of GaAs:C through a step bunching mechanism.