SURFACTANTS - PERFECT HETEROEPITAXY OF GE ON SI(111)

The hetero growth of Ge on Si results in formation of 3D clusters with an uncontrolled defect structure. Introduction of a monolayer of a su rfactant completely changes the growth mode to a 2D-layer growth (Fran k van der Merwe) with a continuous and smooth Ge film on Si(111). The surfactant is not incorporated but segregates and floates on the growi ng Ge film. The saturation of the dangling bonds of the semiconductor reduces the surface free energy and drives the strong segregation. The effect on the growth process is the selective change of activation en ergies which are important for diffusion and the mobility of the Ge. U p to a thickness of 8 MLs (MonoLayers) the misfit-related strain of th e pseudomorphic Ge film is relaxed by formation of a micro rough surfa ce. This allows a partial relaxation of the Ge towards its bulk lattic e constant which would not be possible for a flat and continuous film. For thicker Ge films the misfit of 4.2% is relieved by a periodic dis location network, which is confined to the Si-Ge interface. Ge-films t hicker than 20 MLs are free of defects and completely relaxed to the G e bulk lattice constant: a model system for perfect heteroepitaxial gr owth.