Investigation on the improved radiation hardness of silicon detectors with high oxygen concentration

We present an investigation on the influence of the oxygen concentration on radiation-induced changes in the effective doping concentration of silicon detectors. Diodes fabricated from silicon with interstitial oxygen content ranging from below 2×1014 to 9×1017 cm−3 have been irradiated with fast neutrons up to a fluence of 2×1015 cm−2. Our main interest focused on the so-called stable damage component in the change of the effective doping concentration being of prime importance for the application of silicon detectors in high-energy physics experiments. We demonstrate, that with a high oxygen enrichment the donor removal is appreciably reduced, reaching a value of only 10% of the initial doping concentration for [Oi]=9×1017 cm−3, while for normal detector grade material with [Oi] below 5×1016 cm−3 that value is 60–90%. Furthermore, we show that the fluence proportional introduction of stable acceptors is independent of the oxygen concentration with an averaged introduction rate of (1.49±0.03)×10−2 cm−1. Only one material was found exhibiting a significantly smaller value of about 0.6×10−2 cm−1 and thus indicating the possibility to suppress the radiation-induced acceptor creation by material modification. Finally, we show that the experimental findings disagree in several important aspects with predictions made by microscopic defect kinetics models, leaving the physical background of some of the measured data as an open question.