SPECTRAL RESPONSE OF THE PHOTOCONDUCTIVITY OF POLYCRYSTALLINE CHEMICALLY VAPOR-DEPOSITED DIAMOND FILMS

Photoconductivity and photovoltaic signals of diamond films were measured at 300 K between 0.5 eV and 2 eV. We obtained bands around 0.5,1.08, and 1.38 eV, and a plateau around 1.9 eV, which are ascribed to transitions from the valence band to localized states in the gap. The concentration of defects involved in the 1.08 eV band decreases after annealing at 600-degrees-C. Different polarization offsets are needed to cancel these bands. This difference is ascribed to the occurrence of different defects according to the orientation of the crystallites under the contact. Space-charge zones are assigned to diamond in contact with an intermediate layer under the contact.