STRAINED-LAYER GROWTH AND ISLANDING OF GERMANIUM ON SI(111)-(7 X 7) STUDIED WITH STM

The growth of in situ prepared germanium layers on Si(111)-(7 x 7) has been studied as a function of substrate temperature and coverage. At room temperature, Ge grows in irregular clusters arranged in an ordered array on the substrate and the (7 x 7) reconstruction is preserved. At elevated temperature, in the submonolayer range triangular islands form with preferred growth in [112BAR] direction. The islands show Si-like (7 x 7) and (5 x 5) DAS reconstruction. Ge nucleates preferentially at step edges and at (7 x 7) domain boundaries. Coverages over 2 ML result in a completely (5 x 5) reconstructed layer. On substrate with a (square-root 3 x square-root 3)R30-degrees adatom arrangement after boron segregation, the Ge epilayer also exhibits DAS reconstructions of the same kind found on the pure Si substrates. Above 4 ML the formation of 3D islands is observed, which show mainly (113) and (111) facets. The islands are relaxed and show a mixture of c(2 x 8), c(2 x 4), and (2 x 2) reconstructions known for bulk Ge(111), when they are grown below 450-degrees-C. At a higher deposition temperature a (7 x 7) reappears on top of the 3D islands. Defects emerging from the bulk have been imaged.