Self-organization of Ge islands on high-index Si substrates

Abstract

Films of Ge were grown on Si(113) and Si(331) substrates by molecular-beam epitaxy (MBE). We found that the Ge films grow in the Stranski-Krastanow (SK) mode on both substrates. The SK islands are bounded by facet planes, and have a wirelike shape on Si(113) and a dotlike shape on Si(331). The resulting island shapes are stable equilibrium ones, and are strongly governed by the mechanism of anisotropic strain relief. Moreover, multilayers of coherent Ge islands were stacked on a Si(113) substrate with spacer layers of Si by MBE. In the multilayers of Ge/Si, the wirelike Ge islands become more uniform as the number of layers is increased at a growth temperature of 400 \ifmmode^\circ\else\textdegree\fi{}C. When the temperature is 450 \ifmmode^\circ\else\textdegree\fi{}C, the shape of the islands changes from wirelike in the first Ge layer to dashlike in the sixth Ge layer. This temperature-dependent self-organization is caused by inhomogeneous strain distributions induced by the buried Ge islands that are vertically aligned in the Ge/Si multilayers.