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The semiclassical relationships for the complex refractive index are used to find the regions of integration of the Kramers-Kronig dispersion relation required to yield the spectral dependence of the optical properties of semiconducting materials in the vicinity of the plasma resonance of the charge carriers with a prescribed accuracy. The refractive index n and the absorption coefficientκ of heavily doped Si in the vicinity of the plasma resonance of the charge carriers are determined by the Kramers-Kronig method and by the method of two media. The values of n andκ obtained by these methods are in good agreement with values calculated on the basis of the Drude-Lorentz semiclassical theory of dispersion.

The reflection coefficient R and the phase angleϕ of the reflected electromagnetic wave are calculated with an account of various scattering mechanisms (scattering by ionized impurity and by optical phonons) for wavelengths in the 2-mm range at room temperature. Simplified semiclassical equations for the complex reflection coefficient R* are shown to be valid. The equations are used to calculate R and ϕ for n-type GaAs as functions of the dimensionless frequencies y = ω/ωp and ωpτ. The experimental values of R and ϕ for n-type GaAs single crystals at 2.2 mm agree with the theoretical values, within the experimental error. The concentrations and mobilities determined from the experimental data agree well with the results of Hall measurements.