LAYER-BY-LAYER GROWTH OF GERMANIUM ON SI(100) - STRAIN-INDUCED MORPHOLOGY AND THE INFLUENCE OF SURFACTANTS

Germanium grows on pure Si(100)-(2 x 1) in the Stranski-Krastanov mode. Layer-by-layer growth is found for coverages below 3 ML before the onset of 3D islanding. In this regime the morphology of the Ge layer is strongly influenced by the misfit of 4.2% between layer and substrate. Around 1 ML aligned missing dimer defects are created which form a semiperiodic (2 x 12) arrangement. With increasing coverage this periodicity is gradually compressed and reaches a (2 x 8) reconstruction around 2.3 ML. This behaviour is discussed in terms of partial relaxation of the local strain. When further Ge layers grow on this (2 x N) arrangement, only part of the missing-dimer defects of the lower layer are buried and a network of trenches partly reaching down to the substrate remains. Layer-by-layer growth up to higher coverage can be obtained using As as a "surfactant" during growth. Under these conditions no (2 x 8)-like arrangement is found. Up to 12 ML Ge coverage the layer grows free of defects forming extremely anisotropic Ge islands. At higher coverage a network of trenches arises which decorate an array of V-shaped defects previously found with TEM. The arrangement and the start of the overgrowth of these defects is studied.