Se-induced 3d core-level shifts of GaAs(110)

We present ab initio pseudopotential calculations of 3d core-level shifts of the surface atoms for clean and Se-deposited GaAs(110) surfaces. We are able to explain the experimental findings for the clean GaAs(110) surface in the picture of the initial-state model. If relaxation effects are accounted for we find a distinct overestimation of the surface core-level shifts (SCLS) both for As and Ga atoms with respect to experimental results. We conclude that final-state effects play only a minor role in the dynamics of the photoemission process for the GaAs(110) surface. In order to clarify the surface chemistry of the SeGaAs(110) system we determine the SCLS of the species involved for a series of structural models. Only one of these models gives rise to a reasonable agreement between calculated and measured SCLS. Therefore we strongly support a geometry where each surface As atom is substituted by Se and one further Se binds to the surface Ga atom.