Novel mechanism for the onset of morphological instabilities during chemical vapour epitaxial growth

A novel mechanism leading to the onset of step bunching instabilities during chemical vapour epitaxial growth on vicinal substrates is presented. It is based on the coupling between the surface densities of diffusing precursor molecules and of adatoms, in the presence of Ehrlich-Schwoebel barriers at step edges. We propose and investigate a simple two-particle model accounting for this coupling, and we are able to show that step flow growth is unstable against step pairing. This is contrary to what happens in one-particle models for, say, molecular beam epitaxy, where Ehrlich-Schwoebel barriers oppose step pairing during step flow growth.