Structural, mechanical and optoelectronic properties of cubic Be_xMg_1−xS, Be_xMg_1−xSe and Be_xMg_1−xTe semiconductor ternary alloys: a density functional study

Structural, mechanical and optoelectronic features of cubic Be_xMg_1−xS, Be_xMg_1−xSe and Be_xMg_1−xTe alloys have been explored by DFT-based FP-LAPW approach. Nonlinear reduction in lattice constant, but increment in bulk modulus and each of the elastic constants C₁₁, C₁₂ and C₄₄, occurs with increasing Be-concentration x in each system. All the specimens exhibit elastic anisotropy. Specimens at x = 0 . 0, 0.25 and 0.50 show ductility, but remaining specimens at x = 0 . 75 and 1.0 show brittleness. Each ternary alloy is a direct (Γ-Γ) band gap ( E_g ) semiconductor. Almost linear decrease in E_g with increase in x is observed in each alloy system. Ionic bonding exists among the constituents of all specimens. The occupied valence chalcogen-p as initial and unoccupied conduction Be-3s, 2p and Mg-4s, 3p as final states play a key role in optical transitions. Nature of variation of zero-frequency limit in each of the ε 1 (ω), n (ω) and R (ω) spectra with x is opposite to, while critical point in each of the ε 2 (ω), k (ω), σ(ω) and α(ω) spectra with x is similar to, the nature of variation of E_g with x. (author)