he introduction of a surfactant changes the growth in the Si(111)/Ge system from islanding to a continuous film. A Sb monolayer floats at the growth front without detectable incorporation in the growing film. The surfactant strongly influences the growth kinetics and prevents intermixing or indiffusion of Ge or Si. Up to 8 ML thickness the Ge film is completely strained and pseudomorphic; for thicker films the strain due to the 4.2% misfit is relieved by the generation of defects, which are finally all confined in a dislocation network at the interface. Low-defect, fully relaxed epitaxial Ge films of arbitrary thickness can be grown. Similarly, low-defect relaxed Si can be grown on Ge(111). Medium-energy ion scattering, high-resolution transmission electron microscopy, x-ray-photoelectron spectroscopy, and Raman scattering show that the crystal quality of these Ge films is excellent.