Identification of the conduction-band photoemission in time-resolved two-photon photoemission spectroscopy of Si surfaces

We study photoemissions from Si(111)-(7x7) and Si(001)-(2x1) surfaces by means of time-resolved two-photon photoemission spectroscopy. The peak from the conduction-band minimum (CBM) of bulk Si electronic states has been identified unambiguously in the photoemission spectra for both surfaces, together with peaks from their intrinsic surface states. The CBM photoemission is excited selectively by p-polarized probe light with photon energy of around 5 eV. In terms of the one-step model of photoemission, we conclude that the CBM photoemission results from the transition to evanescent final states induced by the surface photoelectric effect.