Investigation of radiation damage in a Si PIN photodiode for particle detection

The spectral response of a Hamamatsu S5821 Si PIN photodiode was investigated with a 2 MeV proton microbeam with high lateral resolution as a function of particle fluence and applied bias following irradiations with the same particles at the same energy without bias. It has been found that for reasonable high electric fields in the detector, between 10 and 100 V applied reverse bias, the signal amplitude (or charge collection efficiency) decreases linearly, whereas spectral peak FWHM increases within the investigated beam fluences up to 5 × 1011 protons/cm2. Since these detrimental changes vary inversely with the electric field, therefore operating the detector at the highest possible bias value will minimize the influence of the radiation damage on the spectral performance.