The spectral bandshape of the ν3 (1136 cm-1) vibration of oxygen in silicon and dilute silicon-germanium alloys

At room temperature, the ν3 (1136 cm-1) absorption band of oxygen in silicon and Si1-xGex alloys consists of dozens of components, masking the properties of the individual transitions. Here, experimental data are presented for the evolution of the ν3 band in the temperature range 0 < T < 300 K and the composition range 0 ≤ x ≤ 0.066. The vibrational potential for Si:O is developed to provide accurate fits to the absorption data. The potential predicts properties consistent with published studies, including hydrostatic stress experiments. Extending the model to Si1-xGex allows the properties of the alloy-induced Oi-I, Oi-II and Oi-III components to be investigated accurately to higher values of x than hitherto. The properties of Oi-I are understood as perturbations by Ge atoms of Si:O, and Oi-III is rationalized in terms of off-axis movement of the O atom resulting from the nearby Ge atom. Challenges to theory are: the behaviour of Oi-II, understanding the strain fields generated by Ge atoms in Si, and the reduced coupling of the ν2 and ν3 modes with increasing amplitude in the ν2 mode.