LONG-TERM INSTABILITIES IN THE DEFECT ASSEMBLY IN IRRADIATED HIGH-RESISTIVITY SILICON DETECTORS

Transformation of radiation induced, carbon related defects in high re sistivity silicon detectors under multistep irradiation and annealing has been investigated in connection with the problem of reverse anneal ing of the effective space charge concentration, N-eff, in the space c harge region of irradiated detectors. Kinetic behavior of these defect s as possible candidates which affect N-eff has been studied using C-D LTS (capacitance deep level transient spectroscopy) technique after ro om temperature and elevated temperature annealing. Defect transformati on has been identified in the form the decay of radiation induced inte rstitial 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 degrees C) annealing and obeyed the secon d order reaction. Successive steps of irradiation and annealing were p erformed, which stimulated excessive concentration of the C-i-O-i comp lex; generated additional centers in silicon increased oxygen content from heat treatment applied in the detector manufacturing. The results imply that the instability in the defect assembly in irradiated silic on can arise from the complexes including impurities of carbon and oxy gen.