Equilibrium phase diagrams for the elongation of epitaxial quantum dots into hut-shaped clusters and quantum wires

摘要

The formation of self-assembled nanoislands is an important and much-studied feature of strained layer epitaxial growth. The varied island shapes such as pyramids, hut clusters, and elongated nanowires are considered promising building blocks for nanodevice applications. However, even some basic aspects of their growth and energetics are not fully understood. In particular, for Ge on Si (001), it has been recently proposed that the low surface energy of {105} facets renders the (001) surface unstable even neglecting bulk strain energy. Here we calculate how the competition between strain, surface energies, and edge energies determines the equilibrium shapes of epitaxial islands. In particular, we examine the novel regimes that can arise when the (001) surface becomes unstable against faceting. Our calculations thus provide an overview of the equilibrium island shapes as a natural starting point for consideration of possible kinetic effects.