Resonant interaction between localized and extended vibrational modes in Si: 18O under pressure.

The interaction between localized and extended vibrational modes in solids is of central importance in understanding how local vibrational modes decay into phonons. Interstitial oxygen (O(i)) in silicon is a model system for studying such interactions. Using hydrostatic pressure, we have brought the antisymmetric stretch mode of (18)O(i) in silicon into resonance with the second harmonic of the (18)O(i) resonant mode. Infrared spectroscopy was used to observe an anticrossing between these two vibrational modes at pressures near 4 GPa. A model of the interaction between these modes produced excellent agreement with the experimentally observed frequencies and linewidths.

Thermal double donors and quantum dots.

Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in (16)O, (18)O, and mixed isotopic samples are consistent with a model involving [110] aligned oxygen chains made up of an insulating core lying between electrically active ends. The model also explains the minute spin density observed on oxygen in TDD(+) as well as the piezospectroscopic tensors of the donors. The analogy between the thermal donors and quantum dots is emphasized.