Enhanced optical and thermoelectric properties of ZnS monolayer and stacked bilayer compared with bulk

Abstract

In this study, we report the structural, electronic, optical and thermoelectric properties for three different forms of ZnS : bulk (ZnS-B), stacked bilayer (ZnS-BL) and monolayer (ZnS-ML), using first-principles of full-potential density functional theory calculations and semiclassical Boltzmann transport theory. Our results show that ZnS-BL and ZnS-ML with relatively low formation energies of about 152 meV/atom and 209 meV/atom respectively could be exfoliated from ZnS bulk and stabilized in a structure like that of graphene. The optimized ZnS-ML gives a planar structure whereas AB stacking bilayer gives low buckling effect of about 0.003 Å. The calculated electronic band structures and optical properties using TB-mbj approximation of the above structures reveal that their relatively large and direct electronic band gap (4.31 eV for ZnS-ML and 3,94 for stacked ZnS-BL) and their optical performances like low reflectivity and high transparency in the visible light with a widening of the optical window make them a candidate for future opto-electronic devices. Based on electron transport coefficients, we found a larger power and merit factors values, for ZnS-ML and ZnS-BL than ZnS-B, which imply an inherent advantage in their electrical transport properties and make them a potential two-dimensional material comparable to other known good thermoelectric materials.