Synchrotron photoemission studies of the Sb-passivated Si surfaces: Degenerate doping and bulk band dispersions

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Abstract
Synchrotron photoemission of the Sb-covered Si(001), Si(111), and Si(110) surfaces revealed that the Fermi-level position crosses the conduction-band minimum (CBM) of Si for Sb coverages approaching a one-monolayer saturation limit. Momentum-resolved photoemission of the Sb-saturated Si(001) and Si(110) surfaces showed the existence of an occupied initial state located near the CBM. The photoemission intensity of the state has been examined as a function of photon energy with constant initial-state difference spectroscopy which showed various resonances occurring due to transitions to different final states from the CBM. The metallic character of the surface is shown to be due to degenerate doping in the near-surface region. Core-level spectroscopy of Sb/Si(111) and Sb/Si(001) revealed that the Si atoms in the near-surface region are converted to exhibit a bulklike arrangement after Sb coverage. The Sb saturation of Si(111) and Si(001) was found to allow the measurement of the bulk band-dispersion relations along the high-symmetry Γ-Λ-L and Γ-Δ-X directions over a wide photon-energy range (37–153 eV). Strain-reduction mechanisms in the near-surface region are discussed. The measured CBM-state resonances and the Si(001) bulk band transitions indicate that the effective mass of the free-electron-like final band changes for varying photon energies.