Irradiation of thin diamond detectors and radiation hardness tests using MeV protons

Although numerous studies have confirmed the superb radiation hardness of diamond for high-energy (above 100 MeV) protons, almost no data have been reported in the MeV energy range. Because the interaction mechanism that dominates the displacement damage cross section is different for these two energy regimes, it could be misleading to simply extrapolate the results of previous papers down to low energies. Therefore, the radiation tolerance of a 50 μm thick single-crystal CVD diamond detector was tested by irradiating it with 4.5 MeV protons. The scanning microbeam allowed for the selective introduction of damage to a small area of the detector. The ion beam-induced current (IBIC) was used to monitor the charge collection efficiency (CCE) degradation due to the electrically active defects produced. The irradiation was stopped when a signal degradation of nearly 3% was observed. For comparison, the procedure was repeated on a 50 μm thick silicon surface barrier detector (SSBD), for which a significantly higher proton fluence was required to reach the same signal decrease as in the diamond detector. This result can be explained by the different recombination rates of the vacancies and interstitials created in the two materials. The transport properties of electrons and holes in the damaged and virgin areas of the diamond detector were also investigated by 500 keV protons and 6 MeV carbon ions as short-range IBIC probes. The mobility-lifetime products calculated for both charge carriers after fitting the single-carrier Hecht equation indicated that there was more pronounced electron trapping by the radiation-induced defects. The frequently reported effect of polarization in diamond was successfully avoided for 500 keV protons but still remained for 6 MeV carbon ions because an order of magnitude higher ionization rate.