Development of chemical vapour deposited diamond films for particle detector applications

The high resistance against defect generation by particle bombardment favours diamond over other materials for particle detector applications, especially in the light of increased particle flux densities in high energy physics experiments. The limited availability, in former times hindering the introduction of diamond particle detectors, has been overcome by chemical vapour deposition of diamond films. However, for the application of polycrystalline CVD diamond as a particle detector, the charge collection efficiency, expressed in terms of the product of the carrier lifetime, the mobility and the electric field strength, generally referred to as the Schubweg or more recently the charge collection distance, has to be increased. We investigated the influence of gas composition and substrate temperature in a microwave plasma deposition process on optical absorption of the diamond films and their charge collection efficiency for minimum ionizing particles. ..The charge collection distance been determined by exposing diamond films metallized with Ti-Pt-Au contacts to beta particles from a radioactive 90Sr source with maximum energy of 2.28 MeV. The collection efficiency correlates linearly with field strength up to typically 1 kV/cm. The signal slowly saturates at higher field strengths due to increased phonon creation and the resulting decrease of mobility. Collection efficiencies of up to 35% have been measured. We also address the dose dependence of the collection efficiency, as it has been shown, that the efficiency increases under continuous irradiation with ionising particles and light in the far UV. It is believed that the filling of vacant traps is the mechanism for this phenomenon, called priming. We discuss different priming gains and times for different samples. ...