Dielectric function inCdxHg1−xTemixed crystals

Reflectivity spectra of ${\mathrm{Cd}}_x{\mathrm{Hg}}_{1-x}\mathrm{Te}$ mixed crystals are measured at 8 K in the far-infared spectral region: 40-125 μm with special emphasis on the semimetal-semiconductor transition ($x\simeq 0.15$). The dielectric function is analyzed as a sum of contributions: Electron interband transitions with the transitions ${\Gamma }_8\to {\Gamma }_8$ for $x<\mathrm{}0.15\mathrm{}$ and ${\Gamma }_8\to {\Gamma }_6$ for $x>\mathrm{}0.15\mathrm{}$, calculated within the assumption of nonparabolic bands; phonon contribution given by a two-mode behavior for all $x$ calculated with a phenomenological model taking into account long-range interactions and plasmon contribution. The experimental results can be accounted in the frame of the adiabatic approximation for all concentrations.