Interaction between localized and extended modes of oxygen in silicon

The interaction between localized and extended vibrational modes in solids is of central importance in understanding how local vibrational modes (LVMs) decay into phonons. In this study, we have investigated interstitial oxygen (O-i) in silicon as a model 'laboratory' for such local-extended mode interactions. Using hydrostatic pressure and infrared spectroscopy, we brought the stretch mode of O-18(i) in silicon into resonance with a second harmonic of the O-18(i) resonant mode. The resonant interaction results in an avoided crossing between the modes. In addition to this anti-crossing behaviour, the line width abruptly increases, due to a dramatic decrease in lifetime as the LVM enters the two-phonon continuum. A model of the interaction between these modes produced excellent agreement with the experimentally observed frequencies and line widths. (C) 2003 Elsevier B.V. All rights reserved.