Evidence for Internal Rotation in the Fine Structure of the Infrared Absorption of Oxygen in Silicon

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Abstract
Interpretation of the spectra of silicon saturated with oxygen highly enriched with O18 confirms that oxygen is located in an interstitial site. The over‐all features of the absorption indicate that the oxygen is in a nonlinear Si2O configuration. The fine structure in the asymmetric Si–O stretching vibration and its temperature dependence can be largely explained by motion of the oxygen in a potential barrier with six‐fold symmetry. A symmetry analysis of this process predicts additional structure some of which has now been observed under higher resolution. The spectra of oxygen contaminated silicon containing 2% germanium corroborate our explanation of the fine structure. The potential barrier hindering rotation of the oxygen about the axis joining its two bonded silicons has been ascribed to the surrounding silicon lattice. Calculation of the potential shows that as the oxygen rotates it can also wobble. Since the fine structure indicates that the ground‐state splitting due to rotation is near 2 cm—1, the barrier hindering rotation is about 200 cal/mole. Calculation of this barrier then indicates that the maximum wobble angle is 0.2° and the Si–O–Si angle near 150°.

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