THE INTERPLAY OF SURFACE-MORPHOLOGY AND STRAIN RELIEF IN SURFACTANT MEDIATED GROWTH OF GE ON SI(111)

The growth of Ge on Si is strongly modified by surface active species called surfactants. While the effectiveness of Sb as a surfactant in forcing layer-by-layer growth of Ge on Si(111) and in creating a misfit adjusting dislocation network confined to the Si/Ge-interface has been demonstrated in previous studies, the dynamic growth process on an atomic scale leading to this result is still unknown. The relevance of the stress on surface morphology and the growth mode of Ge on Si(111) is presented in a detailed in situ study by spot profile analysing low energy electron diffraction during the deposition. The change from islanding to layer-by-layer growth is seen in the oscillatory intensity variation of the (00)-spot. To relieve the strain the Ge-film forms a microscopically rough surface of small triangular and defect free pyramids in the pseudomorphic growth regime up to 8 monolayers. As soon as the pyramids are completed and start to coalesce, strain relieving defects are created at their base, finally arranging to the dislocation network. After the overgrowth of the dislocations the surface smoothes again showing a much larger terrace length. The periodic dislocation network at the interface gives rise to an elastic deformation of the surface, which results in a spot splitting in LEED. Thus, for the first time the dynamics of the formation of a dislocation network has been observed in situ during the growth process. Surprisingly, the dislocation network is already completed to 70% immediately after 8 monolayers of coverage, which is attributed to the micro-rough surface morphology, providing innumerous nucleation sites for dislocation.