Optical Properties of MBE-Grown Hg_1−xCd_xSe

In this work, we present a study on the temperature-dependent infrared absorption spectra of Hg_1−xCd_xSe grown by molecular beam epitaxy (MBE) on GaSb (211) substrate, having a nominal x-value of 0.21. For temperatures below 200 K, the observed optical bandgap is found to correspond to the Fermi energy level rather than the intrinsic bandgap, which is quantitatively explained by the Burstein–Moss shift due to the presence of a background electron concentration of 3.5 × 10¹⁶ cm⁻³. In addition, empirical formulae for calculating both the absorption edge and intrinsic absorption coefficient in the Kane region have been derived from the previously reported absorption spectra of Bridgeman-grown Hg_1−xCd_xSe samples (0.15 ≤ x ≤ 0.3). By employing the empirical expressions, the infrared transmission spectra have been modeled based on the characteristic matrix method, and the x value profile of the sample along the growth direction has been determined, which is in good agreement with the experimental results obtained from secondary ion mass spectrometry (SIMS) depth profiling combined with Rutherford backscattering spectrometry (RBS).