Optical Absorption in HgTe and HgCdTe

Absorption and reflectivity near the fundamental absorption edge have been measured in the HgTe-CdTe alloy series for CdTe concentrations of up to 28%. In the HgTe rich region, the edge shifts to longer wave-lengths with decreasing temperature. For HgTe, the absorption rises to 2×${10}^4$ ${\mathrm{cm}}^{-1\mathrm{}}$ at $\hslash \omega =0.6\mathrm{}$ eV. Absorption did not decrease below 1.4×${10}^3$ ${\mathrm{cm}}^{-1\mathrm{}}$ at room temperature. The theory of optical absorption in zincblende compounds is reviewed. Absorption in this alloy series agrees with theory for direct transitions with an energy-independent matrix element evaluated by Kane for InSb. Analysis of reflectivity in HgTe indicates an electron effective mass of $0.02m$ at 100°C.