FORMATION AND CHEMICAL-STRUCTURE OF THE AU/SI(111) INTERFACE

The formation of the Au/Si(111) interface was investigated by photoemission and partial-electron-yield spectroscopy using synchrotron radiation, as well as by electron-excited Auger-electron spectroscopy. For n-type Si(111), the Fermi level is found to shift by 0.43 eV toward the center of the band gap due to band bending at the interface. The chemical structure of the interface depends quite critically on the thickness of the deposited Au layer: for very low Au coverages, THETA < 2 angstrom, Au forms an unreacted adlayer; in the intermediate range, 2 less-than-or-equal-to THETA less-than-or-equal-to 25 angstrom, a reacted layer with a composition close to Au3Si is found; in the high-coverage range, THETA > 25 angstrom, the interfacial layer has a sandwich structure, with an unreacted metallic Au phase buried underneath a reacted layer. The critical Au thickness for chemical interaction between Au and Si(111) is explained in terms of the evolving electronic structure of Au with increasing Au coverage.