Deep defect levels in standard and oxygen enriched silicon detectors before and after **6**0Co-gamma-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 left angle bracket 111 right angle bracket and left angle bracket 100 right angle bracket 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 **6**0Co-gamma-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after **6**0Co-gamma-irradiation by C-DLTS are the electron traps VO//i, C//iC//s, V//2( = /-), V //2(-/0) and the hole trap C//i O//i. The main difference between standard and oxygenated silicon at low dose values can be seen in the introduction rate of C//iC//s compared to C //iO//i. For highly oxygenated silicon the introduction of C//iC//s is fully suppressed, while the sum of the introduction rates g(C//iC//s)+g(C//iO//i) is independent on the oxygen concentration.