Theory of Absorption of Electromagnetic Radiation by Molecule-Ion Traps inn−Siandn−Ge

A new mechanism of absorption of electromagnetic radiation at low temperatures in $n$-type silicon and germanium has been investigated. The wavelength region is from 0.01 to 0.1 cm for Si and from 0.035 to 0.5 cm for Ge. Donor concentrations up to 2 × ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ in Si and 6 × ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$ in Ge and compensations up to 0.1 were considered. The model used was that of the photon-induced transitions of electrons between the $1s {\sigma }_g$- and $2p {\sigma }_u$-like states of ionized donor pairs. The formula for the absorption coefficient is derived and numerical results are presented. The role of the ionized-donor-pair molecule-ion traps in hopping processes is also discussed.