The photosensitive, nominally undoped nanocrystalline diamond films were grown on insulating substrates at a relatively low temperature below 600C. The films were exposed to hydrogen plasma and then briefly to oxide plasma. This treatment significantly reduced the surface conductivity and enhanced the bulk photosensitivity. The broad optical spectral range (200-2000nm) photocurrent and optical absorption spectra were measured by the dual-beam photoconductivity, Fourier-transform photocurrent spectroscopy in amplitude modulated step scan mode, optical transmittance and reflectance and photothermal deflection spectroscopy. The photo-ionization cross-section spectrum of the undoped nanocrystalline diamond films was dominated by the non-diamond phase with the photo-ionization threshold energy at about 1eV. At 350C, the thermal annealing increased the concentration of defects related to the non-diamond phase and deteriorated the UV photosensitivity. The significant increase of the optical absorption was observed after annealing at 500C. The hydrogenation can reduce to some extend the defects created by the thermal annealing.

The Influence of Thermal Annealing on the Electronic Defect States in Nanocrystalline CVD Diamond Films. Z.Remes, A.Kromka, J.Potmesil, M.Vanecek: Physica Status Solidi A, 2008, 205[9], 2158-62