Surfactant coverage and epitaxy of Ge on Ga-terminated Si(111)

We have investigated the role of surfactant coverage and bonding for growth of Ge on Si(111). At 470°C Ge grows on Si(111)-(7×7) in a Stranski-Krastanov fashion. Preadsorption of 1-ML Ga at 500°C forms a Ga(111)-(6.3×6.3) structure and alters the Ge growth mode from three-dimensional (3D) islanding to continuous film formation. However, the epitaxial layer contains defects, caused by the presence of domain boundaries of both A- and B-type material. Growth properties depend strongly on the initial Ga coverage: if a (3×3) surface with 1/3-mL Ga is used, a modified Stranski-Krastanov growth mode is observed, with 3D islands of a uniform predominant thickness.