The effect of oxygen impurities on radiation hardness of FZ silicon detectors for HEP after neutron, proton and gamma irradiation

Radiation hardness for fast neutrons, high energy protons and Co-60 gamma rays of planar detectors processed from highly oxygenated silicon detectors obtained by using the high temperature (1200 degrees C), long time (> 200 hours) oxidation technology, are compared with standard silicon detectors. For fast neutron irradiation it is found that there is no advantage of using highly oxygenated silicon FZ detectors as compared to the standard ones in terms of full depletion voltage degradation as measured a few days after radiation. For a gamma ray dose of 250 Mrad, the standard detectors of all resistivities (1 k Omega cm to 5.6 k Omega cm) invert the space charge sign, while there is little change in space charge density for oxygenated ones. Far proton irradiation, the rate in full depletion voltage increase (beta) of oxygenated detectors is 2.3 times less than that of standard detectors. The difference in radiation hardness is explained in terms of effect of radiation induced disorder regions (clusters of vacancies) on the introduction rates of divacancies in the oxygenated silicon.