The 3942-cm−1optical band in irradiated silicon

Uniaxial stress perturbations are reported on the 3942-${\mathrm{cm}}^{\mathrm{-}1}$ (488-meV) zero-phonon line common to irradiated Czochralski-grown silicon. We show that the line occurs at a monoclinic I center, with the electric dipole perpendicular to the principal axis of the center. Carbon and oxygen isotope doping experiments show that the optical center contains at least one carbon atom and at least one oxygen atom. Irradiation of tin-doped Czochralski-grown Si reduces the rate of production of 3942-${\mathrm{cm}}^{\mathrm{-}1}$ absorption, suggesting that vacancies may also be required in the formation of the centers. We find no evidence for other electronic states of the 3942-${\mathrm{cm}}^{\mathrm{-}1}$ center with energies similar to the states taking part in the 3942-${\mathrm{cm}}^{\mathrm{-}1}$ transition. Consequently this center provides the first opportunity to apply simple vibronic sideband theory to an absorption band in silicon. We show that the shape of the phonon sideband, its temperature dependence, and the temperature dependence of the zero-phonon intensity may all be understood with use of established theory. However, we draw attention to the problem of trying to understand the temperature dependence of the width and of the energy of the zero-phonon line, and also its isotope shift. In samples which have received relatively low irradiation doses compared with their carbon content, the 3942-${\mathrm{cm}}^{\mathrm{-}1}$ absorption increases upon annealing near 150?deC, before being destroyed at ∼225 °C. This effect is not understood.