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 consequent irradiation and annealing has been investigated concerning the problem of reverse annealing of the net effective concentration N_eff in the space charge region of the irradiated detectors. Kinetic behavior of these defects as the possible candidates to affect the N_eff has been studied by the C-DLTS (capacitance deep level transient spectroscopy) technique after room temperature and elevated temperature annealing. Defect transformation consists in the decay of radiation induced interstitial carbon which follows the equation of a first order reaction and occurs with simultaneous generation of the 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 annealing and obeyed the second order reaction. Successive steps of irradiation and annealing were repeated which stimulated the excessive concentration of the C_i-O_i complex and generation of additional centers in silicon detectors with an increased oxygen content originated from heat treatment applied in the detector manufacturing. The results imply that the instability in the defect assembly in the irradiated silicon can arise from the complexes including contaminations of carbon and oxygen