Novel Janus α-Au4XY (X/Y = S, Se, Te) monolayers with ultra-high carrier mobility: A first-principles study

In this paper, we theoretically propose a series of Janus $\alpha$-Au${}_4$XY (X/Y = S, Se, Te; X $\ne$ Y) monolayers and investigate their structural stability, electronic features, and transport properties based on first-principle calculations. It is indicated that Janus $\alpha$-Au${}_4$XY monolayers have a structurally stable and can be synthesized experimentally. Janus $\alpha$-Au${}_4$XY monolayers exhibit a low Young’s modulus and their mechanical features are slightly anisotropic. At the ground state, Janus $\alpha$-Au${}_4$XY monolayers possess semiconducting characteristics with very steep band dispersions near the conduction band minimum, which is expected to ultra-high electron mobility. The electronic features of Janus $\alpha$-Au${}_4$XY are highly sensitive to the biaxial strains ${\varepsilon }_{xy}$, particularly the applied compressive biaxial strains. Interestingly, the transitions from the semiconductor to the metal phases are observed in all three configurations of $\alpha$-Au${}_4$XY at ${\varepsilon }_{xy}=-6\text{\%}$. Janus $\alpha$-Au${}_4$XY monolayers exhibit superior transport characteristics with the electron mobility reaching up to $3.20\times 10^5$ cm${}^2$V⁻¹s⁻¹ ($\alpha$-Au${}_4$SSe monolayer). Our findings not only explore the outstanding electronic and transport features of Janus $\alpha$-Au${}_4$XY nanostructures but also indicate their potential applications in nanoelectronics and nanoelectromechanical devices.