Surfactant-stabilized strained Ge cones on Si(001)

Abstract

The formation of circular cone-shaped Ge islands (12\ifmmode^\circ\else\textdegree\fi{} cones) has been observed for the growth of eight monolayers of Ge on Si(001) at 700 \ifmmode^\circ\else\textdegree\fi{}C using Sb as a surfactant. The Ge cones are strained and grow pseudomorphically, adopting the Si lattice constant. They have a tilt angle of 12\ifmmode^\circ\else\textdegree\fi{} and are composed of [117]-, [105]-type, and all intermediate facets. The island-size distribution is peaked around a typical size of \ensuremath{\sim}300--400 \AA{}, which results from a formation process under equilibrium conditions for diffusion of the Ge atoms. Growth at lower temperatures down to 300 \ifmmode^\circ\else\textdegree\fi{}C with Sb as a surfactant results in epitaxial but very rough Ge films which show a high degree of disorder.