Optical homogeneity analysis of Hg_1−xCd_xTe epitaxial layers: How to circumvent the influence of impurity absorption bands?

Optical absorption and photoluminescence spectroscopies are standard tools for analysis of HgHg_1−xCd_xTe epitaxial layers in terms of homogeneity of the mole-fraction (x). For technological relevant layer thicknesses of ∼10 μm, both techniques may show dissimilar results, in particular if doped layers are investigated. This is due to defect levels, which impact to the results obtained by both techniques in different ways. We systematically investigate this behavior by analyzing two sets of HgCdTe layers, one set intrinsically doped by Hg-vacancies, the other extrinsically doped by arsenic (As). A model is outlined and applied to the experimental results, which consistently explains even non-monotonous temperature-shifts of the spectra. Eventually, guidelines for optical homogeneity tests are given. While transmission measurements are most reliable, when carried out at low temperature, where the defect level are frozen out, photoluminescence provides best results at ambient temperature, where band-states are increasingly populated. Both approaches help to reveal intrinsic material properties.