Študij sevalnih poškodb silicijevih detektorjev za eksperimente z visoko luminoznostjo na trkalniku LHC

Radiation damage of the silicon bulk will play an important role in the vertex detectors in the future experiments at LHC. To study its macroscopic effects, high resistivity p-n-n diodes were irradiated with neutrons at the TRIGA research reactor of Jožef Stefan Institute in Ljubljana. Irradiation fluences were in the range from 10^13 to 2.5x10^14 cm2 of equivalent 1 MeV neutrons. Development of effective doping concentration and reverse current during and after irradiations was studied under controlled conditions (bias, temperature). Long term annealing of effective doping concentration was studied to determine the dynamics of the process responsible. Results obtained from a set of unbiased diodes kept at 20"C gave conclusive evidence that, at least during the initial stage, time development can be described by a first order process. Flux dependence of defect creation has been checked in the flux range from 2x10^8 to approx 5x10^15 n/cm2s. No significant difference among the samples was observed in any of the studied properties. Influence of bias voltage on defect development was discovered. Fully biased samples were found to have about a factor 2 higher values of N_eff after beneficial annealing. After removal of bias, the difference anneals out exponentially with two time constants of about 40h and 6 weeks at 20"C. No influence of bias voltage on reverse current was observed.