Novel Janus group III chalcogenide monolayers Al 2 XY 2 (X/Y = S, Se, Te): first-principles insight onto the structural, electronic, and transport properties.

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 2 XY 2 (X/Y = S, Se, Te; X ≠ Y) monolayers by using the density functional theory. Our calculations demonstrate that most of the models of Al 2 XY 2 (except for Al 2 STe 2 monolayer) are dynamically and mechanically stable. By using the hybrid functional, all models of Al 2 XY 2 are semiconductors with an indirect bandgap. Meanwhile, Al 2 TeS 2 monolayer is found to be metal at the Perdew-Burke-Ernzerhof level. Due to the vertical asymmetry structure, an intrinsic built-in electric field exists in the Al 2 XY 2 and leads to a difference in the vacuum levels between the two sides of the monolayers. Carrier mobilities of Al 2 XY 2 monolayers are high directional anisotropic due to the anisotropy of their deformation potential constant. Al 2 XY 2 monolayers exhibit high electron mobility, particularly, the electron mobility of Al 2 SeS 2 exceeds 1 × 10 4 cm 2 V -1  s -1 , suggesting that they are suitable for applications in nanometer-sized electronic devices.