Moderate direct band-gap energies and high carrier mobilities of Janus XWSiP2 (X = S, Se, Te) monolayers via first-principles investigation

Abstract

Two-dimensional (2D) Janus materials with extraordinary properties are promising candidates for utilization in advanced technologies. In this study, new 2D Janus XWSiP₂ (X = S, Se, Te) monolayers were constructed and their properties were systematically analyzed by using first-principles calculations. All three structures of SWSiP₂, SeWSiP₂, and TeWSiP₂ exhibit high energetic stability for the experimental fabrication with negative and high E_coh values, the elastic constants obey the criteria of Born–Huang, and no imaginary frequency exists in the phonon dispersion spectra. The calculated results from the PBE and HSE06 approaches reveal that the XWSiP₂ are semiconductors with moderate direct band-gaps varying from 1.01 eV to 1.06 eV using the PBE method, and 1.39 eV to 1.44 eV using the HSE06 method. In addition, the electronic band structures of the three monolayers are significantly affected by the applied strains. Interestingly, the transitions from a direct to indirect semiconductor are observed for different biaxial strains ε_b. The transport parameters including the carrier mobility values along the x direction μ_x and y direction μ_y were also calculated to study the transport properties of the XWSiP₂. The results indicate that the XWSiP₂ monolayers not only have high carrier mobilities but also anisotropy in the transport directions for both holes and electrons. Together with the moderate and tunable energy gaps, the XWSiP₂ materials are found to be potential candidates for application in the photonic, photovoltaic, optoelectronic, and electronic fields.