Electronic density of empty states of Ge/Si(111) epitaxial layers: Theory and experiment

The structural and morphological properties of thin Ge layers deposited on Si(111)7 x 7 substrate kept at room temperature and subsequently annealed a t several temperatures have been investigated using near-edge x-ray absorpt ion spectroscopy (XAS) at the Ge L edges. Experimental data have been compa red with spectra calculated by a multiple-scattering approach in order to o btain the best-fitting interface model. Our results indicate an amorphous g rowth at room temperature, for coverages ranging from 3 to 14 ML. Two diffe rent behaviors are observed after annealing for Ge coverages below and abov e 3 ML, the so-called critical thickness. For very thin layers, XAS suggest s the formation of a continuous crystalline structure driven by strong inte rmixing processes. Ge layers thicker than the critical thickness have been found to form three-dimensional islands characterized by a lattice-paramete r relaxation and dispersed on a wetting layer. [S0163-1829(99)04731-1].