  We investigate the growth kinetics on vicinal GaAs(001) surfaces by making
detailed comparisons between reflection high--energy electron--diffraction
specular intensity measured near in--phase diffraction conditions and the
surface step density obtained from simulations of a solid--on--solid model.
Only by including a barrier to interlayer transport and a short--range
incorporation process of freshly--deposited atoms can the simulations be
brought into agreement with the measurements both during growth and during
post--growth equilibration of the surface.
