Photoemission Partial Yield Measurements of Unoccupied Intrinsic Surface States for Ge(111) and GaAs(110)

Abstract

Energy-resolved photoemission-yield spectroscopy measurements are reported for transitions from $3d$ core levels to empty surface states and conduction-band states. Unoccupied surface-state bands are observed in the band gap with peaks about 0.2 and 0.9 eV above the valence-band maxima (${E}_{V}$) of Ge(111) and GaAs(110), respectively. These surface-state bands cause the well-known Fermi-level (${E}_{\mathrm{F}}$) pinning at the surface (${E}_{\mathrm{F}}\ensuremath{-}{E}_{V}=0$) for Ge(111) and the range of pinning (${E}_{\mathrm{F}}\ensuremath{-}{E}_{V}=0 \mathrm{to} 0.6$ eV) for doped GaAs(110).