Separate measurement of electron and hole mean drift distance in CVD diamond

A method to measure independently the electron and hole mean drift distance (CCD) in CVD diamond is presented. Very high quality CVD diamond films were grown, and used as particle detectors. Their efficiency is measured as a function of the particle penetration depth under 5.5 MeV Am-241 alpha-particles irradiation. The data are then fitted with a theoretical formula for the carrier mean drift distances derived from a properly modified Hecht model. Simultaneous fit of spectra collected for both positive and negative detector bias gives a separate evaluation of the mean drift distances of each carrier type. The alpha-particle penetration depth is controlled either using air as an absorbing layer or varying the particle incidence angle in the 0-80degrees range. The latter setup is demonstrated to provide higher accuracy. The results show that in our sample the electron and hole CCD are comparable in the as grown state. However, in the pumped state (i.e. after the detector is pre-irradiated with beta-particles) the hole contribution is much greater than the electron one, showing that the pumping process is much more effective on hole traps than on electron traps.