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

The position of the Fermi level E₅ relative to the valence-band maximum Eₕ has been determined from accurate measurements of the Si 2p core-level position relative to E₅. As a reference, we use p-doped samples with a Ga overlayer and n-doped samples with a Cs + O overlayer where E₅ is pinned near the valence-band maximum and conduction-band minimum, respectively. We obtain E₅-Eₕ=0. 400. 03 eV for low-step-density cleaved Si (111) - (21) and E₅-Eₕ=0. 630. 05 eV for annealed Si (111) - (77). Stepped cleavage surfaces are characterized by E₅-Eₕ=0. 46 eV and exhibit larger surface core-level shifts and a shift of the dangling-bond states towards lower binding energy.