Application of free-carrier absorption to N-ZnSe materials characterization

Quantum theory has been applied to calculations of free-carrier absorption in N-ZnSe (including all major scattering mechanisms and screening). The electron concentration n, dependence of the free-carrier absorption coefficient α, was calculated as a function of the ionized impurity concentration and the compensation ratio θ. An inherent limit to α, αinh, was determined at photon wavelengths, λ, of 3.3, 5, and 10 μm. At 10 μm, log αinh (cm−1)≂log n (cm−3)−15.9 for 1014≲n (cm−3)≲1017. A second experimental parameter, the derivative logarithmic absorption coefficient p, is shown to provide an unambiguous method for uniquely determining n and θ, when used in conjunction with α‖λ. The relation of n (cm−3)≂6.7×1015 (3.5 −p) α (cm−1) is proposed for λ=10 μm. Experimental data from the literature are analyzed in this scheme and values of n determined by Hall-effect measurements are shown to be in excellent agreement with theoretical predictions.