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 co re-level photoemission spectroscopy excited with synchrotron radiation sour ce. The SeS2-treated surface consists of a chemically stratified structure of several atomic layers thickness. Arsenic-based sulfides and selenides re side in the outermost surface layer while gallium-based selenides are adjac ent to the bulk GaAs substrate. The shift of the surface Fermi level within the band gap was monitored during controlled thermal annealing, allowing f or the identification of the specific chemical entities responsible for the reduction in surface band bending. Arsenic-based species are removed at lo w annealing temperature with little shift of the Fermi level. Gallium-based selenides are shown to be associated with the unpinning of the surface Fer mi level. (C) 1999 American Institute of Physics. [S0021-8979(99)06602-5].