Bandstructure modulation of two-dimensional WSe2 by electric field

By means of density functional theory computations, we study band-gap tuning in multi-layer WSe2 sheets by external electric fields. It shows that the fundamental band gap of WSe2 film continuously decreases with an increasing vertical electric field, eventually rendering them metallic. The critical electric fields, at which the semiconductor-to-metal transition occurs, are predicted to be in the range of 0.6–2 V/nm depending on the number of layers. This gap-tuning effect yields a robust relationship, which is essentially characterized by the giant Stark effect (GSE) coefficient S, for the rate of change of band gap with applied external field. The GSE coefficient S is proportional to the number of layers and it can be expressed as (n − 1)c/2.