Refractive index enhancement effect in Hg_1-xCd_xTe near the fundamental GAP

The refractive indices of Hg_1-xCd_xTe bulk samples with the composition x=0.276, 0.309, and 0.378 were measured by infrared spectroscopic ellipsometry at room temperature in the energy regions which were below, across, and above the fundamental band gap. An obvious refractive index enhancement effect was observed in the refractive index spectra for each composition. The energy position of the maximal refractive index value approximately equals to that of the band gap. The refractive index versus wavelength λ above the band gap for x between x=0.279 and 0.378 was modeled with Sellmeier dispersion relationship: n²(λ)=a₁+a₂/λ²+a₃/λ⁴+a₄/λ⁶.