Ellipsometric studies of electronic interband transitions inCdxHg1−xTe

Ellipsometric measurements of the dielectric constant of ${\mathrm{Cd}}_x{\mathrm{Hg}}_{1-x}\mathrm{Te}$ alloys were performed at room temperature between 1.8 and 5.5 eV for samples covering the whole range of concentrations. The dependence of the $E_1$, $E_1+{\Delta }_1$, and $E_2$ threshold energies on $x$ was obtained: It is quadratic for $E_1$ and $E_1+{\Delta }_1$ and linear within experimental error for $E_2$. An upwards bowing is found for the spin-orbit splitting ${\Delta }_1$ as a function of $x$. The effect of alloying in broadening the observed structures is relatively small. However, a large decrease of excitonic effects in the $E_1$ and $E_1+{\Delta }_1$ gaps due to alloying has been observed. These results are discussed in the light of recent coherent-potential-approximation calculations.