The vibrational spectrum of interstitial O was measured, under hydrostatic pressures of up to 70kbar and temperatures ranging from 4 to 20K, by means of infra-red spectroscopy. As the pressure was increased, the Oi buckled outwards and the nature of its transverse motion changed from vibrational to rotational. As the motion became more rotational, the splitting between the l = 0 and l = ±1 low-frequency modes decreased. In addition, the splitting between the stretching modes at 1136 and 1128/cm decreased with increasing pressure and could no longer be resolved at pressures greater than 55kbar. In effect, the hydrostatic pressure simulated the situation in Ge, where the Oi atom resided at an off-axis location and behaved like a hindered rotor. It was suggested that hydrostatic pressures could be used to tune the vibrational and rotational modes of impurities and native defects in other semiconductors.

M.D.McCluskey, E.E.Haller: Physical Review B, 1997, 56[15], 9520-3