Localised vibrational mode spectroscopy studies of self-interstitial clusters in neutron irradiated silicon

Abstract

The evolution of self-interstitial clusters in silicon (Si), produced by fast neutron irradiation of silicon crystals followed by anneals up to 750 °C, is investigated using localised vibrational mode spectroscopy. A band at 582 cm−1 appears after irradiation and is stable up to 550 °C was attributed to small self-interstitial clusters (In, n ≤ 4), with the most probable candidate the I4 structure. Two bands at 713 and 758 cm−1 arising in the spectra upon annealing of the 582 cm−1 band and surviving up to ∼750 °C were correlated with larger interstitial clusters (In, 5 ≤ n ≤ 8), with the most probable candidate the I8 structure or/and with chainlike defects which are precursors of the {311} extended defects. The results illustrate the presence of different interstitial clusters In, at the various temperature intervals of the material, in the course of an isochronal anneal sequence. As the annealing temperature increases, they evolve from first-order structures with a small number of self-interstitials (In, n ≤ 4) for the temperatures 50 < T < 550 °C, to second order structures (In, 5 ≤ n ≤ 8) with a larger number of interstitials, for the temperatures 550 < T < 750 °C.