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

Abstract

Structural, mechanical and optoelectronic features of cubic $$\hbox {Be}_{x}\hbox {Mg}_{1-x}\hbox {S}, \hbox {Be}_{x}\hbox {Mg}_{1-x}\hbox {Se}$$ and $$\hbox {Be}_{x}\hbox {Mg}_{1-x}\hbox {Te}$$ 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 $$C_{11}$$ , $$C_{12}$$ and $$C_{44}$$ , 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.