Evidence for a Dielectric Singularity in HgSe and HgTe

New experimental data on the low-temperature mobility of $n$-type HgSe in the concentration range 2×${10}^{17}$-5×${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are compared with a random-phase-approximation (RPA) calculation and a concentration-independent dielectric-constant calculation. The effects of band nonparabolicity and the $p$-like nature of the conduction-band wave function on the scattering calculation are included. The RPA calculation is in excellent agreement with the data, while the results of the concentration-independent dielectric-constant calculation are much too low. New experimental data on HgTe in the concentration range 1.6×${10}^{15}$-4×${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are also examined. At 1.6×${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$, the RPA calculation agrees exactly with experiment, while the concentration-independent dielectric-constant calculation is too low by a factor of 3. In contrast to the case of grey tin, these results strongly support the RPA and hence the dielectric singularity predicted for symmetry-induced zero-gap semiconductors.