Abstract
The impact of ad-dimer diffusion on the morphology of an epitaxially growing stepped surface is studied analytically and by kinetic Monte Carlo simulations. It is shown that if diffusing adatoms are hindered by an Ehrlich-Schwoebel barrier at step edges, ad-dimer diffusion gives rise to a step bunching instability, provided that the corresponding Ehrlich-Schwoebel barrier for ad-dimers is small or vanishing.