Free carrier absorption in heavily doped silicon layers

The standard parametrization of free carrier absorption in silicon predicting a linear dependence of the absorption on carrier concentration is revised, finding that due to several simplifications, it is only applicable up to carrier densities of about 3×1016 cm−3. A parametrization applicable for both p- and n-type silicon and for doping densities as high as 1021 cm−3 is introduced. Using this parametrization, considerably better agreement between the emitter sheet resistance of diffused layers measured by IR transmission and electrical measurements is found, proving the applicability of the enhanced model even for heavily doped layers. Additionally, parameters for the dependence of the refractive index of silicon on doping concentration are given.