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 $E_F-E_V=0.40\mathrm{}\pm 0.03$ eV for low-step-density cleaved Si(111)-(2×1) and $E_F-E_V=0.63\mathrm{}\pm 0.05$ eV for annealed Si(111)-(7×7). Stepped cleavage surfaces are characterized by $E_F-E_V=0.46\mathrm{}$ eV and exhibit larger surface core-level shifts and a shift of the dangling-bond states towards lower binding energy.