Theory of Absorption of Electromagnetic Radiation by Hopping inn-Type Silicon and Germanium. II

Abstract

In a previous paper the absorption of electromagnetic radiation at 0°K in the wavelength region from 100 to 800 μ and from 500 μ to 2.5 cm in $n$-type silicon and germanium, respectively, has been investigated theoretically. The model used was that of photon-induced hopping of an electron between the ground states of donors without phonon participation. The results obtained are compared in the present paper with the theory of Tanaka et al. It is shown that at the short wavelengths the main contribution to the absorption is given by the "polar pairs" neglected in the treatment of Tanaka et al. In Sec. 3 of this paper the contribution to the absorption given by the photon-induced hopping accompanied by the emission of a phonon is investigated. This contribution is rather small in $n$-Ge but important in $n$-Si at short wavelengths. The range of validity of our results is also discussed.