STRAIN RELIEF BY MICROROUGHNESS IN SURFACTANT-MEDIATED GROWTH OF GE ON SI(001)

The deliberate use of surfactants during the growth of Ge on Si(001) p revents the formation of three-dimensional clusters and allows the dep osition of continuous and smooth Ge films. This, however, is not valid for the regime of strained film growth prior to the generation of mis fit-relieving defects. Using Sb as the surfactant, an 8-ML-thick pseud omorphic Ge film exhibits a pronounced microroughness on an angstrom s cale. The average terrace width is only similar to 10 Angstrom. Up to 4-5 vertical layers are simultaneously visible at the surface. This mi croroughness allows the Ge atoms (which are under compressive stress) to relieve lattice-misfit-related strain by partial lateral relaxation towards their bulk lattice constant. This would not be possible for a flat and continuous film. Now the microrough surface is energetically favored and the influence of the growth kinetics is therefore observe d in an increase of the roughness with temperature. Strain-relieving d efects are generated at a coverage of similar to 12 ML and finally lea d to heavily defected films consisting of small-angle mosaics.