A low-cost small-size commercial PIN photodiode

Abstract

Commercial PIN photodiodes, repurposed as particle detectors, have received a lot of attention along the past decades because they can offer a low-cost solution suitable for several applications. The BPX-65 photodiode has been chosen because of its interesting features for measuring electrons in a harsh radiation environment close to the beam of an accelerator. Its electrical characterisation and its application to photon spectrometry have been presented in the companion paper I. Here, its response function (RF) to electrons is investigated using the beam from an electron accelerator with a small energy spread. The empirical expressions for the RF available in the literature have been improved, simplified, and combined to obtain a final form with 7 free parameters: 4 non-linear and 3 linear. A special fitting procedure, which takes advantage of the presence of the linear parameters, is described. The behaviour of these parameters with beam energy and bias is investigated to uncover the physical origin of the three components included in the proposed RF. The interpretation of the features of the spectra is confirmed by Monte Carlo simulations carried out employing the general-purpose PENELOPE/penEasy package. To take into account the charge-collection properties of the device, a simple model has been implemented and is compared to data. It has then been possible to estimate the thickness of the partially dead layer from the experiment.