Photoemission Densities of Intrinsic Surface States for Si, Ge, and GaAs

Photoemission-energy-distribution measurements of intrinsic surface states for Si, Ge, and GaAs have been made using synchrotron radiation in the 7-25-eV range. Occupied intrinsic surface states with Gaussian-shaped optical densities of states about 0.8 to 1.0 eV wide, centered at 0.75, 0.7, and 1.05 eV below the Fermi level, are observed for Si, Ge, and GaAs, respectively. These bands are centered at about 0.45, 0.75, and 0.5 eV below the valence-band edge $E_v$, respectively, rather than at or above $E_v$ as has been generally concluded.