Two-dimensional Janus α-Au2XY (X, Y = S/Se/Te) semiconductors with favourable band gaps and high carrier mobilities predicted by first-principles investigations

Abstract

In this work, two-dimensional Janus α-Au₂XY (X, Y = S/Se/Te) monolayers are designed and their structural stabilities and fundamental properties are investigated using first-principle calculations. We find that the three α-Au₂SSe, α-Au₂STe, and α-Au₂SeTe structures have high energetic, thermodynamic and mechanical stabilities, indicating that experimental fabrication is feasible. In addition, the proposed systems have anisotropic Young’s modulus and Poisson’s ratio values. According to the electronic structure calculations, the α-Au₂XY monolayers are indirect semiconductors with appropriate band gaps for sunlight absorption of 1.06 to 1.33 eV at the Perdew–Burke–Ernzerhof level. The calculation results from the Heyd–Scuseria–Ernzerhof method for the α-Au₂XY monolayers also show indirect band gap semiconductor behavior. Moreover, we utilize the deformation potential technique to analyze the electron and hole mobilities of the α-Au₂XY materials to determine their transport properties. Interestingly, α-Au₂SSe shows an impressive hole carrier mobility of 6258.42 cm² V⁻¹ s⁻¹ along the y-axis. α-Au₂STe and α-Au₂SeTe also have high electron mobilities (μ_e) of 642.21/584.96 cm² V⁻¹ s⁻¹ and 676.56/760.39 cm² V⁻¹ s⁻¹ in the x/y directions, respectively. In view of the remarkable electronic and transport properties, the α-Au₂XY materials are expected to be promising Janus materials for next-generation optical, electronic, and photovoltaic devices.