Pressure tuning of localized and extended vibrational modes in Si:O

Interstitial oxygen in silicon (Si:O) is a model system for the study of vibrational modes in semiconductors. Hydrostatic pressure has been used to probe the vibrational properties of this defect. In this paper, the results of infrared (IR) spectroscopy experiments on Si : O and Si : O are reviewed. As pressure is applied, the oxygen atom buckles outward. This structural change results in a qualitative change in lowfrequency vibrational motion in the [111] plane, as the system transforms from a harmonic oscillator to a rotor. A particularly interesting phenomenon occurs when the Si : O local vibrational mode (LVM) approaches the two-phonon continuum. First, the LVM exhibits an avoided crossing with certain combination modes of the defect. Second, when the LVM enters the two-phonon continuum, the linewidth abruptly broadens, due to a decrease in the lifetime.