Photoemission study of the band gap on cesiated Ge(111)1×1:As

Deposition of small amounts of cesium on the As-terminated Ge(111) surface results in population of the lowest unoccupied surface state centered around the {Γ}{} point in the surface Brillouin zone. By using angle-resolved photoemission we have directly determined the gap between this state and the lone-pair surface state to be 0.85 eV. This result provides support for recent quasiparticle band-structure calculations.