First principle study of electronic and optical properties of WS2(1-x)Se2x obtained by isoelectronic Se substitution on S-site of monolayer WS2

Abstract

Two-dimensional semiconducting transition metal dichalcogenides have recently grabbed attention among the researchers, due to their extraordinary electrical, optical and thermal properties. Also, they have shown their suitability for application in digital electronics, photovoltaic cells, Thermoelectric generators and so on. Still, it is desired to precisely control the material properties to expand their scope of application and revamp the device performance. The substitutional doping technique is one of the widely explored processes, which is conventionally used to modulate the material properties. In the present work, the substitutional doping of selenium at the sulfur site within the WS2 sheet, is used indigenously to improve the electrical and optical response of the material. In doing so, electrical and optical properties of such doped materials are studied by employing density functional theory and linearized Boltzmann transport equation by considering the relaxation time approximation. The study has shown an almost linear variation of electronic band gap energy with the doping percentages. Also, the electron and hole mobility were found to be tailored due to the doping. Notably, hole mobility has shown a noticeable improvement at or near 60 percent of selenium doping. In the last section of the current work, the optical properties are extracted for the doped structures. The WS2 monolayer has shown the highest absorption peak near 3 eV. But for the doped materials, absorption peaks are relatively smaller and left shifted in the energy axis due to their low band gap energies.