Isotope dependence of the lifetime of the 1136-cm-1 vibration of oxygen in silicon

By simply changing the isotopes of the Si atoms that neighbor an oxygen O-i atom in crystalline silicon, the measured decay rate tau of the asymmetric-stretch vibration (nu(3)=1136 cm(-1)) of oxygen (O-i) in silicon changes by a factor of similar to 2.5. These data establish that nu(3) decays by creating one nu(1) symmetric-stretch, local-vibrational mode of the Si-O-i-Si structure. If the residual energy (nu(3)-nu(1)) is less than the maximum frequency nu(m) of the host lattice, as for Si-28-O-16-Si-28 in natural silicon, then it is emitted as one lattice mode, and tau depends on the density of one-phonon states at nu(3)-nu(1). If (nu(3)-nu(1))>nu(m), as for O-16 in single-isotope Si-30 silicon, two lattice modes are created in addition to nu(1), increasing tau. Prediction of tau for a particular defect clearly requires a detailed knowledge of that defect.