Defect evolution in silicon detector material

A numerical kinetics model has been used to investigate the evolution of complex defects in high resistivity silicon detector material during fast neutron irradiation to levels expected at the CERN LHC. The complex V2O is identified as a candidate for a deep-level acceptor state which gives rise to experimentally observed changes in the effective doping concentration. The importance of the initial oxygen impurity concentration in determining the radiation tolerance of the detectors is demonstrated. The characteristics of devices heavily irradiated with 60Co photons are modelled satisfactorily by using a semiconductor simulation in conjunction with the kinetics model. It is postulated that inter-defect transitions between divacancy states in the terminal damage clusters are responsible for apparent discrepancies in the modelling of data from neutron-irradiated devices. This mechanism (if correct) may have important consequences for the prospects of “defect-engineering” a radiation hard device.