Influence of the diamond grain size on the electrical properties of nano-crystalline diamond film detectors

In this work, we developed X-ray radiation detectors with sandwich structure fabricated from nano-crystalline diamond (NCD) films. These NCD films with different grain size ranging from 15 nm to 160 nm were grown on silicon substrates using a hot-filament chemical vapor deposition technique. I–V measurement results indicate that with reducing of the grain size, the resistivity of diamond films decreases from 9.5 × 108 to 6.20 × 107 Ω cm and the ratio of the photocurrent to the dark-current (Iph/Id) of the detectors decreases rapidly from 0.45 to 0.09 at an electric field of 50 kV/cm. Typical spectral response to 5.9 keV 55Fe X-rays shows that counting efficiency and energy resolution of NCD detectors with large grains are better than those of detectors with small grains, due to the less defects and grain-boundaries contained in the film.