The precise evaluation of interstitial O concentrations, [Oi], using infra-red absorption measurements at 1107/cm was investigated in medium-resistivity crystals. The difficulty of accurately measuring [Oi] in these crystals arose from the strong dependence of the internal multiple reflection effect, within samples, upon the free-carrier absorption intensity. The neglect of this effect introduced an error which could be as large as 1ppm[at] for a p-type 1cm crystal. One method of overcoming this difficulty was to eliminate the multiple reflection effect by using p-polarized light that was incident on the sample surface at the Brewster angle. The other method was to eliminate the effect by making multiple reflection corrections which took account of the free-carrier absorption. The results which were obtained by using these infra-red absorption methods were consistent with high-precision results which had been obtained by using secondary ion mass spectrometry.

Y.Kitagawara, M.Tamatsuka, T.Takenaka: Journal of the Electrochemical Society, 1994, 141[5], 1362-4