Electrical properties of diamond surfaces

An attempt is made to explain the presence of a low-resistivity layer on the surface of as-grown undoped CVD films and the unusual nature of the surface sensitivity to various surface treatments in terms of band bending. The experimental results of contact potential difference measurement by Kelvin probe and C Is core level emission spectrum by X-ray photoelectron spectroscopy analysis are correlated reasonably with the band-bending scheme in combination with the Fermi-level position in the bulk and with the pinned surface Fermi level (E(v) + 1.7 eV) in oxygenated samples. The energy band of the as-grown surfaces bends upwards to form an accumulation layer for holes owing to the existence of acceptor-type surface states well below the bulk Fermi level. On the other hand, on oxygen-terminated surfaces produced by oxygen-ambient annealing or oxygen-plasma treatment, there is a depletion layer for holes because of donor-type surface states existing about 1.7 eV above the valence band. The origin of these surface states is not known at present.