Numerical simulation of radiation damage effects in p-type silicon detectors

Abstract

Abstract In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable approach to optimize the long-term radiation hardness of silicon detectors. In this work, we present a numerical model for the simulation of radiation damage effects in p-type silicon, developed within the general-purpose device simulator DESSIS. The model includes radiation-induced deep-level recombination centers in the semiconductor band-gap and the Shockley–Read–Hall statistics. In particular, two deep-level defects have been introduced: one located at EC−0.42 eV, corresponding to a single charge state divacancy and a second one located at EC−0.46 eV, corresponding to a single charge state tri-vacancy. For simulation purposes we have considered a simple, two-dimensional test structure, consisting of a single diode of 40 μm width and 300 μm depth, surrounded by a 6 μm wide guard ring. The n+ implant region depth is 1 μm, with donor concentration of ND=1018 cm−3 implanted on a high-resistivity p-type substrate (NA=5×1012 cm−3). The results of simulations adopting the proposed radiation damage model for p-type substrate have been compared with experimental measurements carried out on similar test structures irradiated with neutrons at high fluence. A good agreement with the experimental data has been obtained for the depletion voltage and diode leakage current. The simulated current damage constant (α=3.75×10−17 A cm−1) is in satisfactory agreement with values reported in the literature. A preliminary study of charge collection efficiency as a function of the fluence is also reported.