Chemical bonding and electronic properties of SeS2-treated GaAs(100)

SeS2-passivated n-type GaAs (100) surfaces, formed by treatment of GaAs in SeS2:CS2 solution at room temperature, were studied with high-resolution core-level photoemission spectroscopy excited with synchrotron radiation source. The SeS2-treated surface consists of a chemically stratified structure of several atomic layers thickness. Arsenic-based sulfides and selenides reside in the outermost surface layer while gallium-based selenides are adjacent to the bulk GaAs substrate. The shift of the surface Fermi level within the band gap was monitored during controlled thermal annealing, allowing for the identification of the specific chemical entities responsible for the reduction in surface band bending. Arsenic-based species are removed at low annealing temperature with little shift of the Fermi level. Gallium-based selenides are shown to be associated with the unpinning of the surface Fermi level. (C) 1999 American Institute of Physics. [S0021-8979(99)06602-5].