Study of the V\(_2^0\) state in neutron-irradiated silicon using photon-absorption measurements

Pieces of \(n\)-type silicon with 3.5 k\(\Omega \cdot \)cm resistivity have been irradiated by reactor neutrons to fluences of (1, 5 and 10) \(\times 10^{16}\) cm\(^{-2}\). Using light-transmission measurements, the absorption coefficients have been determined for photon energies, \(E_\gamma \), between 0.62 and 1.30 eV for the samples as irradiated and after 15 min isochronal annealing with temperatures between 80{\deg}C and 330{\deg}C. The radiation-induced absorption coefficient, \(\alpha_\mathit{irr}\), has been obtained by subtracting the absorption coefficient for non-irradiated silicon. The \(E_\gamma \)-dependence of \(\alpha_\mathit{irr}\) shows a resonance peak, which is ascribed to the neutral divacancy, V\(_2^0\), sitting on a background, and \(\alpha_\mathit{irr} (E_\gamma )\) is fitted by a Breit-Wigner line shape on a parameterized background. It is found that at an annealing temperature of 210{\deg}C the V\(_2^0\) intensity is reduced by a factor 2, and that at the meV level, the position and the width of the fitted Breit-Wigner do not change with irradiation dose and annealing.