Free-Carrier Absorption in n-Type Indium Arsenide

The reflectivity and transmittance at near-normal incidence of three single-crystal samples of n-type indium arsenide having carrier concentrations of 4.7×1016, 9.4×1016, and 4.5×1017 cm−3 are reported. The measurements were made in the spectral region between 5 and 20 μ and at temperatures of 300° and 80°K. These results were used to compute the real and imaginary parts of the dielectric constant at selected wavelengths. The free-carrier contribution to the dielectric constant at a given wavelength was calculated by subtracting the lattice contribution from the total dielectric constant. The lattice contribution was estimated from the dielectric constant of a multicrystalline sample having a small free-carrier concentration. The free-carrier absorption coefficient was obtained from the corresponding free-carrier dielectric constant. Comparison of these experimental free-carrier absorption coefficients with those calculated from classical dispersion theory shows poor agreement of both magnitude and wavelength dependence. However, the results at 300°K for the two highest carrier concentrations are in good agreement with the theory and calculations of Haga and Kimura. The agreement supports their conclusion that the major scattering agents for electrons in InAs at 300°K are optical phonons and impurities.