Analyzing the electronic and optical properties of bulk, unstrained, and strained monolayers of SrS2 by DFT

Abstract

Density functional theory (DFT) calculations were conducted for the electronic and optical properties of the bulk, unstrained and strained monolayers of SrS2. Electronic band structures of the bulk SrS2 indicated an indirect bandgap with 1.32 eV, whereas the SrS2 monolayer displayed a higher indirect bandgap with 1.95 eV. Biaxial tensile strains of different magnitudes cause complex effects by increasing or decreasing the electronic band gaps of the SrS2 monolayer. In contrast, the various biaxial compressive strains always diminish the bandgap energy of the SrS2 monolayer. Furthermore, both bulk and monolayer SrS2 have individual low-dielectric constants suggesting their possible use in microelectronics. In addition, owing to their high refractive indices and optical conductivities in the infrared (IR) region, unstrained bulk and monolayer SrS2 can be effective materials for both IR and solar cell applications. Also, the observed ultraviolet (UV) absorption peaks of unstrained bulk and monolayer SrS2 indicate their suitability as UV absorbers. Strain-dependent optical properties of the monolayer SrS2 were also evaluated. Under biaxial tensile strains between 5% and 25%, monolayer SrS2 demonstrates optical isotropy in which its optical properties remain almost unchanged. However, biaxial compressive strains larger than 10% caused slight variations in the optical properties of the SrS2 monolayer. Obtained phonon dispersions curves for unstrained bulk and monolayer SrS2 prove the dynamical stability of these compounds. Further, SrS2 monolayers SrS2 monolayers under biaxial compressive strains up to 5% and under biaxial tensile strains up to 15% remain dynamically stable.