Intriguing electronic and optical properties of two-dimensional Janus transition metal dichalcogenides

Atomically thin Janus transition metal dichalcogenides (JTMDs) with an asymmetric structure have emerged as a new class of intriguing two-dimensional (2D) semiconductor materials. Using state-of-the-art density functional theory (DFT) calculations, we systematically investigate the structural, electronic, and optical properties of JTMD monolayers and heterostructures. Our calculated results indicate that the JTMD monolayers suffer from a bending strain but present high thermodynamic stability. All of them are semiconductors with a band-gap range from 1.37 to 1.96 eV. They possess pronounced optical absorption in the visible-light region and cover a large range of carrier mobilities from 28 to 606 cm2 V-1 s-1, indicating strong anisotropic characteristics. Significantly, some monolayer JTMDs (e.g., WSSe and WSeTe) exhibit superior mobilities than conventional TMD monolayers, such as MoS2. Moreover, the absolute band-edge positions of the JTMD monolayers are higher than the water redox potential, and most JTMD heterostructures have a type-II band alignment that contributes to the separation of carriers. Our work suggests that the 2D JTMD monolayers are promising for nanoelectronic, optoelectronic, and photocatalytic applications.