Diamond detectors with laser induced surface graphite electrodes

We report on the response of metal-less CVD polycrystalline-diamond pixel sensors under beta-particles irradiation. A 21 x 21 array of 0.18 x 0.18 mm(2). pixels was realized on one side of a 10.0 x 10.0 x 0.5 mm(3) polycrystalline diamond substrate by means of laser induced surface graphitization. With the same technique, a large graphite contact, used for detector biasing, was fabricated on the opposite side. A coincidence detecting method was used with two other reference polycrystalline diamond detectors for triggering, instead of commonly used scintillators, positioned in the front and on the back of the sensor array with respect to the impinging particles trajectory. The collected charge distribution at each pixel was analyzed as a function of the applied bias. No change in the pulse height distribution was recorded by inverting the bias voltage polarity, denoting contacts ohmicity and symmetry. A fairly good pixel response uniformity was obtained: the collected charge most probable value saturates for all the pixels at an electric field strength of about +/- 0.6 V/mu m. Under saturation condition, the average collected charge was equal to =1.64 +/- 0.02 fC, implying a charge collection distance of about 285 mu m. A similar result, within 2%, was also obtained for 400 MeV electrons at beam test facility at INFN Frascati National Laboratory. Experimental results highlighted that more than 84% of impinging particles involved only one pixel, with no significant observed cross-talk effects. (C) 2016 Elsevier B.V. All rights reserved.