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 ($E_{\mathrm{F}}-E_V=0\mathrm{}$) for Ge(111) and the range of pinning ($E_{\mathrm{F}}-E_V=0\mathrm{} \mathrm{to} 0.6$ eV) for doped GaAs(110).