Defect kinetics in novel detector materials

Abstract

Silicon particle detectors will be used extensively in experiments at the CERN Large Hadron Collider, where unprecedented particle fluences will cause significant atomic displacement damage. We present a model of the evolution of defect concentrations and consequent electrical behaviour in “novel” detector materials with various oxygen and carbon impurity concentrations. The divacancy-oxygen (V 2O) defect is identified as the cause of changes in device characteristics during 60Co gamma irradiation. In the case of hadron irradiation, changes in detector doping concentration ( N eff) are dominated by cluster defects, in particular the divacancy (V 2), which exchange charge directly via a non-Shockley–Read–Hall mechanism. The V 2O defect also contributes to N eff. This defect is more copiously produced during 24 GeV/ c proton irradiation than during 1 MeV neutron irradiation on account of the higher vacancy introduction rate, hence the radiation hardness of materials is more sensitive to impurity concentrations in the case of protons than neutrons. We conclude that naı̈ve normalisation of N eff data using hardness factors of radiation sources can be misleading, because point defect introduction rates do not necessarily scale with non-ionising energy loss.