Observation of a Band of Silicon Surface States Containing One Electron Per Surface Atom

We have studied the energy distribution of electrons photoemitted from surface states on the cleaved (111) face of a 0.001-Ω-cm $n$-type Si crystal. We find a 1.8-eV-wide surface band with a peak at 1.1 eV and a shoulder at 0.5 eV below the Fermi energy containing about 8×${10}^{14}$ electrons/${\mathrm{cm}}^2$, i.e., approximately one electron per surface atom. The strong peak lies below the valence-band maximum at the surface. The surface nature of this structure is confirmed by its disappearance when exposed to vacuum contamination at ${10}^{-10\mathrm{}}$ Torr or to oxygen.