Isotope Dependence of the Lifetime of the 1136-cm 1 Vibration of Oxygen in Silicon

0031-9007= By simply changing the isotopes of the Si atoms that neighbor an oxygen Oi atom in crystalline silicon, the measured decay rate of the asymmetric-stretch vibration ( 3 1136 cm 1) of oxygen (Oi) in silicon changes by a factor of 2:5. These data establish that 3 decays by creating one 1 symmetric-stretch, local-vibrational mode of the Si-Oi-Si structure. If the residual energy ( 3 1) is less than the maximum frequency m of the host lattice, as for 28Si-16O-28Si in natural silicon, then it is emitted as one lattice mode, and depends on the density of one-phonon states at 3 1. If 3 1 > m, as for 16O in single-isotope 30Si silicon, two lattice modes are created in addition to 1, increasing . Prediction of for a particular defect clearly requires a detailed knowledge of that defect.