Structural, elastic and optoelectronic characteristics of BexZn1−xS, BexZn1−xSe and BexZn1−xTe alloys-a density functional based FP-LAPW study

Abstract

Structural, elastic and optoelectronic features of BexZn1−xS, BexZn1−xSe and BexZn1−xTe alloys are computed employing DFT based FP-LAPW approach. Structural features with WC-GGA functional show that lattice constant decrease and bulk modulus increase nonlinearly with increase in Be-concentration in each alloy system. The elastic constants C11andC44for cubic specimens increase, whileC12decrease with increase in Be-concentration in each system. Elastically anisotropic specimens at x = 0.0 and 0.25 are ductile, while at x = 0.50, 0.75 and 1.0 are brittle in nature. The electronic properties, computed with mBJ, EV-GGA and PBE-GGA functional, predict each ternary sample as a direct band gap (Γ-Γ) semiconductor. Band gap increases nonlinearly with Be-concentration in each system. Chemical bonding between beryllium and chalcogen are ionic and between zinc and chalcogen are covalent in nature. In optical transitions, chalcogen-p in valence band as initial states and Be-3s, 2p as well as Zn-5s states in conduction band as final states play the leading role. Nature of variation of each of theε1(0), n(0)and R(0)with Be-concentration x is opposite, while critical point in each of the ε2(ω)k(ω),σ(ω) and α(ω) spectra with Be-concentration x is similar to the nature of variation of band gap with Be-concentration in each alloy system.