Optical absorption coefficient of silicon at 1.152 μ at elevated temperatures

The optical absorption coefficient of silicon has been measured at the HeNe near-infrared line (λ = 1.152 μm) from room temperature to 1140 K. The results are compared with the previous less extensive data in the literature, and with the formulation given by Macfarlane et al. [Phys. Rev. 111, 1245 (1958)]. It is found that the absorption is described very well by phonon-assisted indirect transitions across an energy gap having the temperature dependence described by Thurmond.