Long term instabilities in the defect assembly in irradiated high resistivity silicon detectors

Transformation of radiation induced, carbon related defects in high resistivity silicon detectors under multistep irradiation and annealing has been investigated in connection with the problem of reverse annealing of the effective space charge concentration, N_eff , in the space charge region of irradiated detectors. Kinetic behavior of these defects as possible candidates which affect N_eff has been studied using C-DLTS (capacitance deep level transient spectroscopy) technique after room temperature and elevated temperature annealing. Defect transformation has been identified in the form the decay of radiation induced interstitial carbon, which follows the equation of a first order reaction, and the simultaneous generation of C _i-O_i and C_i-C_s complexes. It has been shown that the concentration of the C_i-O_i complex increased at RT (room temperature, 22°C) annealing and obeyed the second order reaction. Successive steps of irradiation and annealing were performed, which stimulated excessive concentration of the C_i-O_i complex; it also generated additional centers in silicon detectors with increased oxygen content from heat treatment applied in the detector manufacturing. The results imply that the instability in the defect assembly in irradiated silicon can arise from the complexes including impurities of carbon and oxygen