SURFACE-MORPHOLOGY AND STRAIN RELIEF IN SURFACTANT-MEDIATED GROWTH OFGERMANIUM ON SILICON(111)

The growth of Ge on Si is strongly modified by adsorbates called surfa ctants. The relevance of the stress on surface morphology and the grow th mode of Ge on Si(111) is presented in a detailed in situ study by h igh resolution low energy electron diffraction (LEED) during the depos ition. The change from islanding to layer-by-layer growth mode is seen in the oscillatory intensity behaviour of the OO-spot. As a strain re lief mechanism, the Ge-film forms a microscopic rough surface of small triangular and defect-free pyramids in the pseudomorphic growth regim e up to 8 monolayers. As soon as the pyramids are completed and start to coalesce, strain relieving defects are created at their base, final ly arranging to the dislocation network. Without the driving force for the micro-roughness, the stress, the surface flattens again showing a much larger terrace length. The formation process of the dislocation network results in a spot splitting in LEED, since the periodic disloc ations at the interface give rise to elastic deformation of the surfac e. Surprisingly the Ge-film is relaxed to 70% immediately after 8 mono layers of coverage, which is attributed to the micro rough surface mor phology, providing innumerous nucleation sites for dislocation.