Pseudopotential studies of co-adsorption of group-V elements and Ge on Si(001) surfaces

We examine the Si(001) surface with co-adsorption of a monolayer of Ge and a monolayer of group V with formation of Si/X/Ge and Si/Ge/X (X=P, As, Sb or Bi). From an energetic point of view, we find that group V segregation is favoured, and the corresponding energy gain increases from P through to Bi. We also find from purely structural considerations that Bi and Sb offer far better substrate relaxations than do P and As. The trend in energy difference between Si/X/Ge and Si/Ge/X is shown to be largely dependent on the electonegativity of the group-Ti layer and the corresponding structural changes induced in the substrate. These considerations have important implications for the choice of surfactant species for the epitaxial growth of Ge on Si(001). (C) 1999 Elsevier Science B.V. All rights reserved.