Performance of monocrystalline diamond radiation detectors fabricated using TiW, Cr/Au and a novel ohmic DLC/Pt/Au electrical contact

Diamond radiation detectors are able to detect deep UV photons, X-rays, gamma rays, electrons, alpha particles, charged ions and neutrons, with a dynamic range in energies spanning from 5.5 eV up to GeV of cosmic rays. Since the bandgap of diamond is 5.5 eV this equates into negligible dark current noise at room temperature with no need for cooling. Metal diamond interfaces play a key role in the performance of the detectors as different metallization techniques lead to either ohmic or Schottky electrical contacts. We investigated the performance of synthetic high purity monocrystalline diamond radiation detectors fabricated with TiW, Cr/Au and a novel metallization technique utilising diamond-like carbon tunnelling junction and Pt/Au as electrical contacts. The investigation was carried out under irradiation with Co-60 γ-rays, Sr-90 electrons and Am-241 α-particles. The experimental results with respect to I –V dark current levels, irradiation photocurrent, signal-to-noise ratio and time response have been compared and discussed. Results show an ohmic behaviour of the DLC/Pt/Au contact, a charge collection efficiency of 100% at an applied electric field of 0.377 V/um for all electrical contacts (under Sr-90 electrons irradiation) at a correspondent dark current value of less than a picoAmpere.The single crystal CVD DLC/Pt/Au diamond radiation detector reported here shows spectroscopic energy resolution of 1.1% at an applied voltage of +450 volts under 5.5 MeV alpha particle irradiation; the experiments also showed a fast response of the novel contact with a transit time pulse of 6 ns. No ‘memory’ or ‘pumping’ effect was observed for the DLC/Pt/Au contact at positive bias; the signal was also stable (fluctuations below 0.5%) and reproducible under Co-60 irradiation, with a signal to noise ratio ≫ 10000:1 and a linearity in the dose rate response.