FAR-INFRARED ABSORPTION BY INTERSTITIAL OXYGEN IMPURITIES IN SILICON-CRYSTALS

To verify our model for the local-mode-coupled low-energy excitation o f the oxygen in silicon [H. Yamada-Kaneta, C. Kaneta, and T. Ogawa, Ph ys. Rev. B 42, 9650 (1990)], we have performed high-resolution far-inf rared absorption measurements for the oxygen lines at 29.3, 37.7, 43.3 , and 48.6 cm(-1). The assignment of these lines to the optical transi tions previously made with our model has been supported by the measure d temperature dependences of the line intensities. Our model that had explained the line energies has further described successfully the tem perature dependence of the line-intensity ratio. This line-intensity r atio is shown to be a manifestation of the quartic anharmonicity (off- center nature) of the potential for the low-energy excitation.