Deep defect levels in standard and oxygen enriched silicon detectors before and after 60Co-γ-irradiation

Capacitance Deep Level Transient Spectroscopy (C-DLTS) measurements have been performed on standard and oxygen-doped silicon detectors manufactured from high-resistivity n-type float zone material with 〈1 1 1〉 and 〈1 0 0〉 orientation. Three different oxygen concentrations were achieved by the so-called diffusion oxygenated float zone (DOFZ) process initiated by the CERN-RD48 (ROSE) collaboration. Before the irradiation a material characterization has been performed. In contrast to radiation damage by neutrons or high-energy charged hadrons, were the bulk damage is dominated by a mixture of clusters and point defects, the bulk damage caused by 60Co-γ-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after 60Co-γ-irradiation by C-DLTS are the electron traps VOi, CiCs, V2(=/−), V2(−/0) and the hole trap CiOi. The main difference between standard and oxygenated silicon at low dose values can be seen in the introduction rate of CiCs compared to CiOi. For highly oxygenated silicon the introduction of CiCs is fully suppressed, while the sum of the introduction rates g(CiCs)+g(CiOi) is independent on the oxygen concentration.