Atomic and electronic structure of S-terminated GaAs(001) surface

Abstract

We have reported, from ab initio calculations, on the changes in the electronic and structural properties due to S adsorption on the GaAs(001) surface. In our investigation, we have considered the experimentally observed (2×6) reconstruction for S coverages of n/12 monolayers (MLs), with n=2, 4, 5, 6, 8, and 10. Electronic energy levels and density of states for all the six coverages of S have been discussed. Using the chemical potential argument our calculations suggest that the reconstruction with S coverage of 10/12 ML (the Tsukamoto model) represents the most energetically preferable structure for S/GaAs(001). However, while this adsorption geometry is consistent with the electron counting model, it does not passivate the GaAs(001) surface electronically. The most effective reduction in the density of states in bulk band gap region is obtained for the coverage of 0.5 ML with five mixed As–S dimers, though this geometry is inconsistent with the electron counting model for chemical passivation of the surface.