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

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