Projection of the annealing behavior of irradiated Si sensors in the LHC environment

The study of the radiation tolerance and subsequent annealing effects on p+-n-n+ silicon micro strip detectors has been performed as a part of R&D program for the preshower detector in the CMS experiment. CMS silicon strip sensors were irradiated with 24 GeV protons at CERN proton synchrotron (PS) to a total fluence of 3×10¹⁴ p/cm². Sensors were stored in freezer after irradiation and I-V and C-V measurements were carried out. Variation in full depletion voltage and leakage current have been studied as a function of annealing time. The breakdown performance of the device actually improves after irradiation due to the beneficial effect of type-inversion. The breakdown voltage increases further with annealing time. However, the leakage current increases tremendously just after irradiation. As the sensors are annealed, there is a drop in leakage current. The rate of annealing is observed to be temperature dependent. Hence in terms of leakage current, it seems that room temperature annealing is beneficial. However, if the sensors are annealed at room temperature, the depletion voltage will start rising after a short period of beneficial annealing. Hence for the silicon detectors to be used for preshower of CMS experiment, the temperature is set to freezer temperature to avoid reverse annealing. The beneficial and reverse annealing time constants are calculated and found to match well with predictions from Ziock parameterization.