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 VO i, C iC s, V 2(=/-), V 2(-/0) and the hole trap C iO 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.