BGaAs epitaxial layers were grown by metalorganic vapour phase epitaxy (MOVPE) on (100) GaAs vicinal substrates using diborane, triethylgallium and arsine as precursors. For growth temperatures of 580 and 610 degrees C, we studied the boron incorporation in the epilayers, their boron surface composition and their growth mode as a function of the diborane flow-rate, using respectively X-ray diffraction, X-ray photoelectron spectroscopy and Atomic Force Microscopy. We observed that increasing the diborane flow-rate strongly favours the development of step-bunching. This trend was related to a pronounced boron enrichment of the surface, as a consequence of a surface segregation of boron. These results suggest that boron behaves as a surfactant during the MOVPE growth of BGaAs and particularly increases the surface diffusion length of gallium adatoms. For excessive diborane flow-rates, a dramatic roughening of the epilayer surface is first observed and then, phase separation occurs. (C) 2008 Elsevier B.V. All rights reserved.