Strain- and electric field-enhanced optical properties of the penta-siligraphene monolayer

Abstract

Two-dimensional (2D) Si-based materials are very attractive for use in electronic devices due to their main advantages, such as hardness, stability and non-toxicity. In this work, we study the electronic and optical properties of the penta-siligraphene (p-Si₂C₄) monolayer with/without effects of biaxial strain (ε_b) and external electric field (E) using density functional theory (DFT). The structural, dynamic and thermal stabilities of the p-Si₂C₄ monolayer were confirmed by its negative formation energy, absence of soft modes in the phonon dispersion curve and small drift in the total energy at standard temperature, respectively. Our results showed that the p-Si₂C₄ monolayer is an indirect semiconductor with a bandgap of 1.39 eV. We found that under the effect of biaxial strain and electric field, a semiconductor-to-metal phase transition occurs and the bandgap depends on both ε_b and E. Indeed, the bandgap decreases under compressive strain and both negative and positive electric fields, while the bandgap increases slightly with a tensile strain of up to 2%. For the optical properties, the p-Si₂C₄ monolayer has a high optical absorption of the order of ∼10⁵/10⁶ cm⁻¹ in both visible/UV ranges and it can be enhanced by biaxial strain. This improvement in optical absorption can increase the range of applicability of p-Si₂C₄ in optoelectronics.