Microscopic analysis of defects in a high resistivity silicon detector irradiated to 1.7×1015 n/cm2

Current-based microscopic defect analysis methods with optical filling techniques, namely current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC), have been used to study defect levels in a high resistivity silicon detector (p⁺-n-n ⁺) induced by very high fluence neutron (VHFN) irradiation (1.7×10¹⁵ n/cm²). As many as fourteen deep levels have been detected by I-DLTS. Arrhenius plots of the I-DLTS data have shown defects with energy levels ranging from 0.03 eV to 0.5 eV in the energy band gap. Defect concentrations of relatively shallow levels (E_t<0.33 eV) are in the order of 10¹³ cm^-3 while those for relatively deep levels (E_t>0.33 eV) are in the order of 10¹⁴ cm^-3. TSC data have shown similar defect spectre. A full depletion voltage of about 27,000 volts has been estimated by C-V measurements for the as-irradiated detector, which corresponds to an effective space charge density (N_eff) in the order of 2×10¹⁴ cm^-3. Both detector leakage current and full depletion voltage have been observed to increase with elevated temperature annealing (ETA), which corresponds to the increase of some deep levels, especially the 0.39 eV level. Results of positron annihilation spectroscopy have shown a decrease of total concentration of vacancy related defects including vacancy clusters with ETA, suggesting the breaking up of vacancy clusters as possible source of vacancies for the formation of single defects during the reverse anneal