Electron transport in MoWSeS monolayers in the presence of an external electric field

The influence of an external electric field on single-layer transition-metal dichalcogenides TX₂ with T = Mo, W and X = S, Se (MoWSeS) has been investigated by means of density-functional theory within two-dimensional periodic boundary conditions under consideration of relativistic effects including the spin-orbit interactions. Our results show that the external field modifies the band structure of the monolayers, in particular, the conduction band. This modification has, however, very little influence on the band gap and effective masses of holes and electrons at the K point, and also the spin-orbit splitting of these monolayers is almost unaffected. Our results indicate a remarkable stability of the electronic properties of TX₂ monolayers with respect to gate voltages. A reduction of the electronic band gap is observed starting only from field strengths of 2.0 V Å^-1 (3.5 V Å^-1) for selenides (sulphides), and the transition to a metallic phase would occur at fields of 4.5 V Å^-1 (6.5 V Å^-1).