UNOCCUPIED SURFACE-STATES ON SI(111)ROOT-3X-ROOT-3-AG

A nearly metallic surface state band is detected on Si(111)root 3 X ro ot 3 Ag by inverse photoemission, Si 2p core level photoemission, and scanning tunneling spectroscopy. The band spans most of the bulk band gap of Si, from the Fermi level at 0.25 eV above the valence band maxi mum all the way to the conduction band minimum, The Fermi level is pin ned over a wide doping range (7 X 10(18) cm(-3) p type to 1.2 X 10(19) cm(-3) n type). The data suggest that the surface band gap expected f rom the even electron count is filled in at room temperature, possibly due to thermal disorder or due to the finite domain size of 10-20 nm. A second, prominent surface feature at 2.2 eV above the valence band maximum is assigned to surface umklapp from (K) over bar to <(Gamma)ov er bar> via a root 3 X root 3 reciprocal lattice vector.