Determination of the Fermi-level pinning position at Si(111) surfaces

Abstract

The position of the Fermi level ${E}_{F}$ relative to the valence-band maximum ${E}_{V}$ has been determined from accurate measurements of the Si $2p$ core-level position relative to ${E}_{F}$. As a reference, we use $p$-doped samples with a Ga overlayer and $n$-doped samples with a Cs + O overlayer where ${E}_{F}$ is pinned near the valence-band maximum and conduction-band minimum, respectively. We obtain ${E}_{F}\ensuremath{-}{E}_{V}=0.40\ifmmode\pm\else\textpm\fi{}0.03$ eV for low-step-density cleaved Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) and ${E}_{F}\ensuremath{-}{E}_{V}=0.63\ifmmode\pm\else\textpm\fi{}0.05$ eV for annealed Si(111)-(7\ifmmode\times\else\texttimes\fi{}7). Stepped cleavage surfaces are characterized by ${E}_{F}\ensuremath{-}{E}_{V}=0.46$ eV and exhibit larger surface core-level shifts and a shift of the dangling-bond states towards lower binding energy.