CHEMICAL BONDING AND STRUCTURE OF THE SULFUR TREATED GAAS(111)B SURFACE

We have investigated the atomic structure and chemical bonding present at sulfur exposed GaAs(111)B-(2X2) surfaces using both scanning tunne ling microscopy (STM) and synchrotron radiation core-level photoemissi on. Exposure of the (2x2) surface to a molecular beam of sulfur leads to the appearance of a (1x1) low-energy electron diffraction pattern w hich becomes increasingly well defined as the sample is annealed. Howe ver, at no stage of the annealing process does the surface display an ordered (1X1) ideal termination. Both the photoemission data and STM i mages show that a large proportion of the As trimer units of the clean (2X2) surface remain after sulfur exposure and annealing to 450 degre es C with strong evidence of sulfur substituting for As in atomic laye rs below the surface. The effect of these reactions is to increase the surface band-bending from that of the clean (2X2) surface. (C) 1995 A merican Institute of Physics.