Optical properties of Hg_xCd_1-xS and Hg_xCd_1-xSe alloys from first principles

Mercury-cadmium chalcogenide alloys are materials of interest for applications in the visible to near-infrared region of the electromagnetic spectrum. Their tunable optical properties make them candidates for use as NIR detectors and quantum dot emitters. In this work we present results from first principles density functional theory calculations of zincblende Hg_xCd_1-xS and Hg_xCd_1-xSe alloys. We compare the band structures and band gap energies from DFT-PBE and HSE hybrid exchange-correlation functionals. We consider excitonic effects on the optical spectra of the binary end components and discuss the influence of spin-orbit coupling on the optical spectra. We also employ the generalized quasi-chemical approximation to predict the optical spectra of intermediate alloy compositions in thermodynamic equilibrium. We find a higher Hg:Cd ratio results in a larger effect on band gap energies from spin-orbit coupling in DFT-PBE, with a less pronounced effect in HSE. We also find minimal changes in the simulated optical spectra due to spin-orbit coupling.