Structural, mechanical and optoelectronic properties of cubic $$\hbox {Be}_x\hbox {Mg}_1-x\hbox {S}, \hbox {Be}_x\hbox {Mg}_1-x\hbox {Se}$$ and $$\hbox {Be}_x\hbox {Mg}_1-x\hbox {Te}$$ semiconductor ternary alloys: a density functional study

Structural, mechanical and optoelectronic features of cubic (hbox {Be}_xhbox {Mg}_1-xhbox {S}, hbox {Be}_xhbox {Mg}_1-xhbox {Se}) and (hbox {Be}_xhbox {Mg}_1-xhbox {Te}) 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 ((Gamma {-}Gamma )) band gap ((E_{mathrm{g}})) semiconductor. Almost linear decrease in (E_{mathrm{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 (varepsilon ₁ (omega )), (n(omega )) and (R(omega )) spectra with x is opposite to, while critical point in each of the (varepsilon ₂ (omega )), (k(omega )), (sigma (omega )) and (alpha (omega )) spectra with x is similar to, the nature of variation of (E_{mathrm {g}}) with x.