First principles prediction of two-dimensional Janus XMoGeN2 (X = S, Se and Te) materials

Motivated by the successful synthesis of two-dimensional MoSi2N4 [Y.-L. Hong et al., Science, 2020, 369, 670-674] and Janus MoSSe [A.-Y. Lu et al., Nat. Nanotechnol., 2017, 12, 744-749], in this work, we propose novel 2D Janus XMoGeN2 (X = S, Se and Te) monolayers using first-principles prediction. The controllable electronic features of Janus XMoGeN2 (X = S, Se and Te) monolayers under an external electric field and strain are also examined. Our predictions demonstrated that 2D XMoGeN2 materials are structurally and dynamically stable. All these 2D XMoGeN2 materials are indirect semiconductors with band gaps of 1.60/2.10, 1.54/2.07 and 1.05/1.56 eV obtained by the PBE/HSE functional for SMoGeN2, SeMoGeN2 and TeMoGeN2 monolayers, respectively. Furthermore, the electronic band gap and band structures of these monolayers are controllable under an external electric field and strain, making them promising candidates for flexible optoelectronics and nanoelectronics. The electric field tunes the TeMoGeN2 monolayer from semiconductor to metal and leads to a change in the band gap. While strain modifies the band gap of the TeMoGeN2 monolayer, giving rise to a shift in the CB from the Γ-M path to the M point and a tendency to transform from semiconductor to metal. Our findings suggest that these novel 2D XMoGeN2 materials are potential candidates for use in future high-performance applications.