The influence of the crystal lattice on coarsening in unstable epitaxial growth

We report the results of computer simulations of epitaxial growth in the presence of a large Schwoebel barrier on different crystal surfaces: simple cubic(001), bcc(001), simple hexagonal(001) and hcp(001). We find that mounds coarsen by a step-edge diffusion-driven process, if adatoms can diffuse relatively far along step edges without being hindered by kink-edge diffusion barriers. This yields the scaling exponents α=1, β=13. These exponents are independent of the symmetry of the crystal surface. The crystal lattice, however, has strong effects on the morphology of the mounds, which are by no means restricted to trivial symmetry effects. Whereas we observe pyramidal shapes on the simple lattices, on bcc and hcp there are two fundamentally different classes of mound, which are accompanied by characteristic diffusion currents: a metastable one with rounded corners, and an actively coarsening configuration, which breaks the symmetry given by the crystal surface.