Infrared optical constants of n-type silicon

The infrared optical constants of n-type Si are determined from reflectance and transmittance spectra. The Drude formula with empirically adjusted, concentration dependent, parameters is used. Its low-wavelength limit is in agreement with recent mobility results. A pronounced difference between As-, P-, and Sb-doped Si is found for the free electron concentration above 10¹⁹ cm^-3. Simple empirical formulae are given for the optical constants as functions of both wavenumber and concentration.