Unoccupied electronic states on GaAs(1̄1̄1̄) (2×2) studied by angle-resolved constant-initial-state photoemission

Angle-resolved off-normal constant-initial-state (CIS) photoemission is shown to be effectively applicable to investigate the unoccupied electronic band structure parallel to the surface above the vacuum level. For the MBE-prepared GaAs(111) (2×2) surface we observe empty bulk band states as well as an electronic state about 13.6 eV above the valence band maximum, the latter revealing a periodicity in the dispersion parallel to the surface characteristic for the (2×2) reconstructed surface. There is no Ga 3d core exciton-decay observed in the CIS-spectra, indicating that the As-terminated surface has no unoccupied Ga-derived dangling bond state