Surface electronic bands of GaAs(110) determined by angle-resolved inverse photoemission.

Abstract

Applying angle-resolved inverse photoemission to cleaved GaAs(110), we have measured the energy dispersion of the unoccupied surface-state bands along the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}--X\ifmmode\bar\else\textasciimacron\fi{} and \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}--X\ifmmode\bar\else\textasciimacron\fi{}' symmetry directions of the surface Brillouin zone. The bands are almost parallel to the known occupied surface-state bands, which implies that only one optical transition feature may occur in optical reflectivity in agreement with the findings of Selci et al. Since we measured the top of the valence band by in situ direct photoemission and used a common Fermi level of a metallic reference sample, we were able to combine occupied and empty surface bands on a common energy scale. However, the surface band gap obtained in this manner is 0.6 to 0.7 eV larger than the optical value of 2.9 eV of Selci et al. We speculate that relaxation effects which act differently in direct and in inverse photoemission may be the reason for this discrepancy.