Photoemission study of Si(111)-Ge(5×5) surfaces

Photoemission spectroscopy was used to study Si(111)-Ge(5×5) surfaces prepared by annealing Ge films deposited onto Si(111)-(7×7) substrates. The Si 2p core-level line shape was modified in going from (7×7) to (5×5) systems. By decomposing the spectra into bulk- and surface-shifted components the changes in line shape were identified as due to selective replacement of Si by Ge in different layers of the substrate, without any drastic change in the surface structure. The Ge 3d core-level line shape for the Si(111)-Ge(5×5) surface was also measured and compared with that for the Ge(111)-c(2×8) surface. These results are discussed in terms of models for the Si(111)-(7×7) structure. A surface state was observed on the Si(111)-Ge(5×5) surface, which gave rise to a metalliclike Fermi edge in the angle-integrated spectra; a similar surface state was observed on the Si(111)-(7×7) surface but not on the Ge(111)-c(2×8) surface.