Asymmetry and shape transitions of epitaxially strained islands on vicinal surfaces

We calculate the shapes of epitaxially strained islands on vicinal substrates, within a fully facetted, two-dimensional model. For nonzero miscut, islands first form as asymmetric "half-pyramid" shapes, with no nucleation barrier even in a fully facetted system. As islands grow, they change shape through a series of first-order transitions. The substrate miscut determines what island types occur in the growth sequence; sufficiently large miscut can stabilize qualitatively asymmetric shapes such as "half domes." Our results are summarized in a phase diagram of shape versus island volume and miscut. The results are consistent with available experiments for Ge on Si.