Exploring the Optical Properties of Hg_1−x Cd _x Se Films Using IR-Spectroscopic Ellipsometry

Abstract

We have used infrared spectroscopic ellipsometry to interrogate the dielectric response of a series of Hg_1−x Cd _x Se samples in a spectral range between 2000 and 40000 nm. Using a standard inversion technique, the experimental data obtained at multiple angles of incidence were modeled to deduce the dielectric function of each sample. The dielectric functions obtained for Hg_1−x Cd _x Se samples allowed us to predict the band gaps for the samples, which increase as a function of the Cd concentration. Next, we modeled the dielectric function as a collection of oscillators, each of which represented a particular transition manifested in the spectrum. The most significant result obtained from this work is the recovery of their doping characteristics from the ellipsometric data. Specifically, two Hg_1−x Cd _x Se samples with x = 0.21 and 0.28, grown on GaSb substrates, show a carrier concentration of 1.6 × 10¹⁷ and 1.8 × 10¹⁸ cm⁻³, respectively. These results are particularly helpful because conventional Hall measurements cannot be used for these specific samples due to the substrates (i.e., GaSb) used to grow them being highly conductive.