Theoretical prediction of novel two-dimensional auxetic material SiGeS and its electronic and optical properties

Abstract

Two-dimensional (2D) materials have aroused tremendous interest due to their great potential in the applications in electronic, optical, and mechanical devices. We theoretically design a new 2D material SiGeS by regularly arranging the Si-S-Ge skeleton of SiH<sub>3</sub>SGeH<sub>3</sub>. Based on first-principles calculation, the structure, stability, electronic properties, mechanical properties, and optical properties of SiGeS are systematically investigated. Monolayer SiGeS is found to be energetically, dynamically, and thermally stable. Remarkably, SiGeS displays a unique negative Poisson's ratio. Besides, SiGeS is an indirect-semiconductor with a band gap of 1.95 eV. The band gap could be modulated effectively by applying external strains. An indirect-to-direct band gap transition could be observed when the tensile strain along x axial or biaxial is greater than +3%, which is highly desirable for applications in optical and semiconductor technology. Moreover, pristine SiGeS has a high absorption coefficient (~10<sup>5</sup> cm<sup>-1</sup>) from visible to the ultraviolet region. Under tensile strain along x, the absorption edge of SiGeS has a red shift, which makes it cover the whole region of solar spectrum. These intriguing properties render SiGeS a competitive multifunctional material for nanomechanic and optoelectronic applications.