Surface states from photoemission threshold measurements on a clean, cleaved, Si (111) surface

Abstract

Very accurate measements of the photoemission yield have been performed on the (111) face of silicon as a function of photon energy in the threshold region down to the ${10}^{\ensuremath{-}10}$ range. Using a set of differently doped samples cleaved in ultrahigh vacuum, one can distinguish between surface- and bulk-state photoelectrons, and determine the approximate shape of the surface-state density (SSD) in the band gap. For the clean surface, the SSD increases from the Fermi level to the top of the valence band, approximately following a $\frac{3}{2}$ power law and does not vanish when reaching the valence band. The effect of doping is computed and leads to an electron escape length of about 12 \AA{}. The effect of steps is briefly mentioned.