Far-infrared study of free carriers and the plasmon-phonon interaction in CdTe

The reflectivity of $n-\mathrm{CdTe}$ has been measured between 16 and 203 ${\mathrm{cm}}^{-1\mathrm{}}$ at room temperature. The single-crystal samples had carrier concentrations $N$ between 5 × ${10}^{16}$ and 1 × ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The data could be fitted by using classical lattice theory and Drude-type free-carrier theory with an energy-independent scattering time. The values of $N$ and mobility $\mu$ obtained from the fits agreed reasonably well with Hall and resistivity values. The agreement was not improved by the introduction of an energy-dependent scattering time for either polar-mode or ionized-impurity scattering. The plasmon-phonon minima were observed and their frequencies were found to be strongly influenced by $\mu$ as well as by $N$. The optical lattice parameters were determined as follows: ${\epsilon }_s=10.2\mathrm{}$, ${\epsilon }_{\infty }=7.1\mathrm{}$, ${\omega }_t=141\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $\Gamma =8.7\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. These results agree well with previous measurements.