Defect-engineering rad-hard particle detectors: the role of impurities and inter-defect charge exchange

摘要

Silicon detectors in particle physics experiments at the CERN Large Hadron Collider will be exposed to unprecedented levels of radiation. The principal obstacle to long-term operation in this environment is changes in detector effective doping concentration (N_(eff)). We present a model of defect evolution during gamma and hadron irradiation which has been combined with Shockley-Read-Hall (SRH) statistics to predict N_(eff) and dark current in irradiated devices. These predictions are compared with experimental results from detectors with various oxygen and carbon concentrations. In the case of gamma irradiation, the electrical characteristics are described satisfactorily by the concentrations. In the case of gamma irradiation, the electrical characteristics are described satisfactorily by the production of divacancy-oxygen (V_2O) defects. In the case of hadron irradiation, however, the experimental data cannot be explained in the conventional SRH picture. We propose a model whereby states in the terminal defect clusters exchange charge directly. This mechanism leads to a marked increase in carrier generation rate and an enhancement in the acceptor-like contribution to N_(eff). We conclude that only limited improvements in radiation hardness to hadrons can be achieved by altering detector impurity levels, since the changes in N_(eff) are dominated by intrinsic defects within the terminal clusters.