Strain engineering of electrical and optical properties of two dimensional hexagonal PbX (X = S, Se) monolayers

Abstract

Strain engineering offers a means to tune the properties of two-dimensional (2D) materials, which is crucial for applications in energy storage, electronics, and optoelectronics. This study investigates the structural stability of two-dimensional hexagonal monolayers of lead sulfide (PbS) and lead selenide (PbSe). It also explores how applied compressive and tensile strains influence the electrical and optical properties of these semiconductors using density functional theory (DFT). The results indicate that PbS monolayers exhibit greater energetic stability than PbSe. We found that the electrical properties of these semiconductors, characterized by indirect band gaps larger than those of their corresponding bulk forms, can be modulated through the application of either compressive or tensile strain. Notably, the transition from an indirect to a direct band gap presents new possibilities for applications in optoelectronics. The peak band gap values for PbS and PbSe monolayers occur at −4% and −2% strain, respectively. Additionally, analysis of the real part of the dielectric function shows that as the structures are compressed, the static dielectric constant increases. The maximum value of the imaginary part, ε₂(ω), for PbX monolayers is calculated for structures under −8% strain. Our results also reveal that the intensity of the absorption peaks decreases under tensile strain.