Origin of enhanced Ge interdiffusion at the initial stage of Ge deposition on Si(5 5 12)-2 × 1: Tensile stress induced by substrate chain structures

Abstract

By combined investigation of STM and synchrotron PES on Ge/Si(5 5 12)-2×1 at 530°C, it has been found that, in addition to the upward-relaxed surface Si atoms, a subsurface Si atom is also readily replaced by an arriving Ge atom at the initial adsorption stage. Such enhanced interdiffusion is due to a unique character of one-dimensional chain structures of the reconstructed substrate, such as π-bonded and honeycomb chains not existing on other low-index Si surfaces such as Si(001)-c(4×2) and Si(111)-7×7, applying a tensile surface stress to the neighbouring subsurface atoms. Interdiffusion of Ge having lower surface energy induces adsorption of the displaced Si atoms on the surface to form sawtooth-like facets composed of (113)/(335) and (113)/(112) with arriving Ge atoms until the surface is filled with those facets. Such displacive adsorption is the origin of high Si concentration of formed facets.