Bandgap engineering of different stacking WS2 bilayer under an external electric field

• The stacking effects on the electronic structures of WS2 bilayers are investigated.
• We study the effects of the van der Waals interaction on the Geometries and stabilities of WS2 bilayers.
• The modification of the band structures of WS2 bilayers by an electric field is dicussed.
• It is shown that the spontaneous electrical polarization exists between the two monolayers of AB conformation.

Effective modulation of physical properties via external control is a tantalizing possibility that would bring two-dimensional material-based electronics a step closer. By means of density functional theory calculations, we systematically examined the effect of external electric field on the bandgap of different stacking WS2 bilayer. It shows that for all cases, the most stable stacking order is the AB conformation, followed by the AA′ stacking fault, which is by only 2.06 meV/supercell less stable than AB. The band gaps of both AB and AA′ configurations decrease monotonically with an increasing vertical external electric field strength except for external electric field along −z direction in the AB conformation. Applying external electric field along +z direction and −z directions has different effects on the band gap of AB conformation, while it has the same effect on the AA′ configuration. The different effects are caused by the spontaneous electrical polarization existing between the two monolayers of AB conformation. This may provide a new perspective on the formation of WS2-based electronic and optoelectronic devices.