High collection efficiency in chemical vapor deposited diamond particle detectors

Diamond is a very attractive material to realise nuclear detectors due do i ts outstanding properties. In order to realise the detectors described in t his work, diamond films were grown on silicon by microwave chemical vapor d eposition (CVD) using an H-2-CH4 gas mixture. The alpha particle spectra we re measured by using a 5.5 MeV Am-241 source. A maximum collection efficien cy eta as high as 70%, with an average value of 50%, was obtained in a 115 mu m thick sample after beta particle irradiation ('priming effect'). These values correspond to collection distances, as calculated by the Hecht form ula, of 250 mu m and 120 mu m respectively (higher than the film thickness) thus demonstrating the very high quality of the samples. Unprimed efficien cy eta = 50% maximum, 30% average was also obtained on other samples. The e fficiency and the resolving power of the detectors were studied as a functi on of the external electric field. A Monte Carlo simulation of the alpha particle detection pRocess was develo ped, and the results compared to the experimental spectra. It is concluded that the priming process saturates in-grain defects limiting the as-grown d etector performance, so that charge collection distance is only limited by grain boundaries located close to the substrate side. Thus, further improve ment can be reasonably obtained by increasing the film thickness and/or by removing the defective layer at the substrate interface. (C) 2000 Elsevier Science S.A. All rights reserved.