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

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 (EV) of Ge(111) and GaAs(110), respectively. These surface-state bands cause the well-known Fermi-level (EF) pinning at the surface (EF-EV=0) for Ge(111) and the range of pinning (EF-EV=0to0.6 eV) for doped GaAs(110). © 1974 The American Physical Society.