Density Functional Investigations of Structural, Mechanical and Optoelectronic Properties of BeSxSe1−x, BeSxTe1−x and BeSexTe1−x Ternary Alloys

Abstract

Density functional full-potential linearized augmented plane wave (FP-LAPW) investigations of structural, mechanical and optoelectronic features of cubic BeSxSe1−x, BeSxTe1−x and BeSexTe1−x ternary alloys are performed. Nonlinear decrease in lattice constant ($$ a_{0} $$), but increase in bulk modulus ($$ B_{0} $$) and each elastic constant ($$ C_{11} $$, $$ C_{12} $$ and $$ C_{44} $$) occurs with increasing dopant chalcogen concentration x in each system. In each specimen, elastic anisotropy, brittleness and dominancy of covalent bonding are observed. Each binary compound and ternary alloy at x = 0.25 and 0.75 is a direct (Γ–Γ) bandgap semiconductor, and ternary alloy at x = 0.50 is an indirect (X–Γ) bandgap ($$ E_{\rm g} $$) semiconductor. Nonlinear increase in bandgap ($$ E_{\rm{g}} $$) with increase in x is observed in each alloy system. Chalcogen-p → Be-3s, 2p optical excitations contribute intense peaks in each spectra of the imaginary part of the dielectric function $$ \varepsilon_{2} (\omega ) $$. The trend of variation of zero-frequency limit in each real dielectric function $$ \varepsilon_{1} (\omega ) $$, refractive index $$ n(\omega ) $$ and normal incidence reflectivity $$ R(\omega ) $$ spectra and critical point in each of the imaginary dielectric function $$ \varepsilon_{2} (\omega ) $$, extinction coefficient $$ k(\omega ) $$, optical conductivity $$ \sigma (\omega ) $$ and optical absorption $$ \alpha (\omega ) $$ spectra with x is opposite and similar, respectively, to the trend of variation of bandgap ($$ E_{\rm{g}} $$) with x.