The absorption coefficient of Si at 1118/cm due to the multi-phonon contribution related to the combination of two transverse optical and one transverse acoustical phonons was measured at the liquid He temperatures. The precise knowledge of this contribution, usually hidden by the absorption band of the unavoidable O impurities, permits the quantitative measurement of interstitial O concentration down to 3 x 1014/cm3.

Measurement of Interstitial Oxygen Concentration in Silicon below 1015atoms/cm3. A.Sassella: Applied Physics Letters, 2001, 79[26], 4339-41