Temperature dependence of the optical properties of Hg1-xCdxTe

The alloy composition of Hg1-xCdxTe should be controlled during growth, so that the desired band gap and the lattice-matched layer may be obtained. In-situ spectroscopic ellipsometry, now commercially available, enables one to acquire spectral data during growth. If one knows the optical dielectric function as a function of alloy composition and temperature, the technique can be fully used to monitor and control temperature, the thickness, and the alloy composition. For this purpose, we first obtained temperature dependent spectral data of Hg1-xCdxTe by spectroscopic ellipsometry (SE). The spectral data of Hg1-xCdxTe with x = 1, 0.235, and 0.344 were obtained from room temperature to 800K in the photon energy range from 1.3 to 6 eV. The spectral data revealed distinctive critical point structures at E-0, E-0 + Delta(0), E-1, E-1 + Delta(1), E-2(X), and E-2(Sigma). Critical point energies decreased and linewidths increased monotonically as temperature increased. The model for the optical dielectric function enabled (i) the critical point parameters to be determined accurately, and (ii) the spectral data to be expressed as a function of temperature within and outside the experimental range.