Distorted Janus Transition Metal Dichalcogenides: Stable Two-Dimensional Materials with Sizable Band Gap and Ultrahigh Carrier Mobility

Transition metal dichalcogenides (TMDs) are ideal layered materials to fabricate field effect transistors (FETs) due to their sizable band gaps and high stability, however, the low carrier mobility limits the response speeds. Here, based on recent experimental progress, we employed first principle calculations to reveal a distorted phase of the Janus TMD, 1T′ MoSSe, which is highly stable, exhibiting a moderate band gap and ultrahigh carrier mobility. We show that 1T′ MoSSe can be obtained via structural transition from the synthesized 2H phase after overcoming an energy barrier of 1.10 eV, which can be significantly reduced with alkali metal adsorption, thus proposing a feasible approach for experimental fabrications. 1T′ MoSSe is predicted to be a semiconductor with a trivial band gap of 0.1 eV (based on Heyd–Scuseria–Ernzerhof calculations), which can be closed to form Dirac nodes and then reopened under strain deformation. Due to the almost linear dispersion of the band states, an ultrahigh electron (hole) mobility of up to 1.21 × 105 (7.24 × 104) cm2/V/s is predicted for the new phase, which is 3 orders of magnitudes higher than traditional counterparts and close to the value of graphene. The high stability, sizable band gap, and ultrahigh carrier mobility in the new Janus systems are expected to be used in high-performance electronics applications.