Mid-infrared dispersion of the refractive index and reflectivity for GaAs

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Abstract
Since the band gap of GaAs is more than 40 times larger than hνTO of the Reststrahlen absorption peak, it would seem natural to assume that dispersion caused by one phenomenon ceases completely before that caused by the other begins. However, that is not rigorously true, and the continuous progression of the refractive index n(hν) is modeled here for situations of room temperature (∼300 K) and low temperatures (<30 K). Attention is paid especially to the consequences for the spectral variation of GaAs reflectivity through the mid-infrared at such temperatures, and the implications for making quantitative deductions about the strengths of weak sub-band-gap absorption processes in this material.