Fourier transform infrared absorption spectroscopy was used to study the evolution of multivacancy-oxygen-related defects in the temperature range 200-300°C in Czochralski-grown Si samples irradiated with MeV electrons or neutrons. A clear correlation between disappearance of the divacancy (V_2) related absorption band at 2767 cm~(-1) and appearance of two absorption bands positioned at 833.4 and 842.4 cm~(-1) at 20 K (at 825.7 and 839.1 cm~(-1) at room temperature) has been found. Both these two emerging bands have previously been assigned to a divacancy-oxygen defect formed via interaction of mobile V_2 with interstitial oxygen (O_i) atoms. The present study shows, however, that the two bands arise from different defects since the ratio of their intensities depends on the type of irradiation. The 842.4 cm~(-1) band is much more pronounced in neutron irradiated samples and we argue that it is related to a trivacancy-oxygen defect (V_3O) formed via interaction of mobile V_3 with O_i atoms or/and interaction of mobile V_2 with VO defects.
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