First-Principles Investigation of Structural, Elastic, Electronic, and Optical Properties of Cd_1−x−yZn_xHg_yS Quaternary Alloys

First-principles calculations have been carried out to explore the zinc and mercury composition-dependent structural, elastic, electronic, and optical properties of zinc-blend specimens under the Cd_1−x−yZn_xHg_yS triangular quaternary system. Each quaternary alloy shows thermodynamic stability. Computed elastic stiffness constants confirm the mechanical stability, ductility, elastic anisotropy, compressibility, plasticity, and mixed type of bonding in each specimen. Calculations with modified Becke–Johnson (mBJ)-generalized gradient approximation (GGA) and GGA+U schemes show that each ternary or quaternary alloy is a direct band gap (Γ–Γ) semiconductor. Carrier transportation in each specimen is significantly dominated by electrons due to their much lower effective mass compared to holes. Electronic transitions from the occupied S-3p state of the valence band to the unoccupied Zn-5s, Cd-6s, and Hg-7s states of the conduction band are exclusively or collectively responsible for the occurrence of intense peaks in the imaginary part of the dielectric function, ε₂(ω), spectra of the considered specimens. The calculated oscillator strengths of quaternary alloys show the presence of a sufficient number of electrons in the unoccupied states of the conduction band beyond 25.0 eV of incident energy during optical excitations.