Degradation of the charge collection efficiency of an n-type Fz silicon diode subjected to MeV proton irradiation

We present the analysis of the charge collection efficiency (CCE) degradation of float zone grown n-type silicon detectors irradiated with 1.3, 2.0 and 3.0 MeV protons. The analysis Was carried out by irradiating small regions (50 x 50 mu m(2)) with a proton microbeam at fluences ranging from 10(11) to 4.10(12) ions/cm(2) and probing the effect of irradiation by measuring the 4.5 MeV Li ion induced charge in full depletion conditions. The CCE degradation as function of the proton fluence shows an unexpected deviation from the linear behavior predicted by the Shockley Read Hall model of carrier recombination. The build-up of excess hydrogen related donors due to proton irradiations is suggested to be the cause of a significant perturbation of the electrostatic properties of the diode, which drastically change the electron trajectories and hence the induced charge mechanism.