Chemical and structural studies of the interactions of molecular sulfur with the GaAs(111)A and GaAs(111)B surfaces

The interactions of sulfur with the GaAs(111)A and (111)B surfaces has been investigated by synchrotron radiation photoelectron spectroscopy. A scanning tunnelling microscopy study has been performed on the sulfur treated GaAs(111)B surface. Clean GaAs(111) surfaces, prepared in UHV by the thermal removal of an As cap, were exposed in situ to a molecular beam of sulfur. Changes in the surface chemistry and the Fermi level position were monitored as a function of annealing temperature. While this treatment results in complex surface chemistry which displays evidence of both surface and sub-surface sulfur-arsenic exchange reactions, the degree of Fermi level movement would indicate that neither of these surfaces are effectively electronically passivated. The implications of this for surface passivation are considered.