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 L₁^c and L₃^c critical points were determined as 2. 400. 15 and 4. 150. 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. 50. 2 eV. The lowest unoccupied surface state on the Si (111) 21 surface at is identified at 1. 20. 1 eV.