Three phonon decay mode of the 1136-cm(-1) nu(3) vibration of oxygen in silicon

The (1136-cm(-1)) nu(3) vibration of oxygen in silicon is known to decay at low temperature primarily by emitting two phonons. We show here that the temperature dependence of the decay is caused by a three-phonon process. In both natural-isotope and single-isotope Si-30, the three-phonon process is identified as the emission of one nu(1) (612 cm(-1)) local mode, one nu(2) low-energy local mode, and one lattice mode of 524 cm(-1) (where the quoted values are for O-16 in natural-isotope silicon). The common assumption that the decay of a vibration proceeds through one dominant process is clearly not applicable here.