CHEMICAL AND STRUCTURAL STUDIES OF THE INTERACTIONS OF MOLECULAR SULFUR WITH THE GAAS(111)A AND GAAS(111)B SURFACES

The interactions of sulfure with the GaAs(111)A and (111)B surfaces ha s been investigated by synchrotron radiation photoelectron spectroscop y. A scanning tunnelling microscopy study has been performed on the su lfur 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 mo lecular 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 displ ays evidence of both surface and sub-surface sulfur-arsenic exchange r eactions, the degree of Fermi level movement would indicate that neith er of these surfaces are effectively electronically passivated. The im plications of this for surface passivation are considered.