Novel Janus group III chalcogenide monolayers Al2XY2 (X/Y= S, Se, Te): First-principles insight onto the structural, electronic, and transport properties
Abstract Motivated by the recent successful synthesis of 2D quintuple-layer atomic materials, for the first time, we design and investigate the electronic and transport properties of Janus Al$_2XY_2$ ($X/Y =$ S, Se, Te; $X \neq Y$) monolayers by using the density functional theory. Our calculations demonstrate that most of the models of Al$_2XY_2$ (except for Al$_2$STe$_2$ monolayer) are dynamically and mechanically stable. By using the hybrid functional, all models of Al$_2XY_2$ are semiconductors with an indirect bandgap. Meanwhile, Al$_2$TeS$_2$ monolayer is found to be metal at the PBE level. Due to the vertical asymmetry structure, an intrinsic built-in electric field exists in the Al$_2XY_2$ and leads to a difference in the vacuum levels between the two sides of the monolayers. Carrier mobilities of Al$_2XY_2$ monolayers are high directional anisotropic due to the anisotropy of their deformation potential constant. Al$_2XY_2$ monolayers exhibit high electron mobility, particularly, the electron mobility of Al$_2$SeS$_2$ exceeds $1\times 10^4$~cm$^2$/Vs, suggesting that they are suitable for applications in nanometer sized electronic devices.