Bismuth-containing c(4 × 4) surface structure of the GaAs(1 0 0) studied by synchrotron-radiation photoelectron spectroscopy and ab initio calculations

Bismuth (Bi) induced c(4 × 4) surface structure of the GaAs(1 0 0) substrate, i.e., the GaAs(1 0 0)c(4 × 4)-Bi surface has been studied with synchrotron-radiation photoelectron spectroscopy and ab initio calculations. The surface was prepared by combining molecular beam epitaxy and in situ electron diffraction methods, and then the sample was transferred to a photoemission chamber without breaking ultrahigh vacuum conditions. Calculations show that the c(4 × 4)β type unit cells, which consist of Bi-Bi and Bi-As dimers, are energetically favored on the surface and that Bi atoms occupy only the topmost atomic sites bonding to the As layer below. The presence of the c(4 × 4)β structure is supported by the comparison of measured and calculated core-level shifts of the GaAs(1 0 0)c(4 × 4)-Bi surface. Simulated scanning-tunneling-microscopy (STM) images, based on the suggested models, are presented for the comparison with future STM measurements.