No 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 ' range. Using a set of differently doped samples cleaved in ultrahigh vacuum, one can distinguish between surfaceand 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 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 A. The effect of steps is briefly mentioned.