Conduction-Band and Surface-State Critical Points in Si: An Inverse-Photoemission Study

From measurements of the dispersion of the lowest two conduction bands in silicon by k-resolved inverse photoemission the energies of the L₁ᶜ and L₃ᶜ critical points were determined as 2.40±{}0.15 and 4.15±{}0.10 eV relative to the valence-band edge, respectively. A comparison with energies derived from photoemission and optical data reveals a large excitonic lowering of the E₁ transition by 0.5±{}0.2 eV. The lowest unoccupied surface state on the Si(111) 2×{}1 surface at Γ is identified at 1.2±{}0.1 eV.