An ab-initio perspective on the electronic and optical characteristics of nanosheet: Role of external electric field

The presence of an external electric field has a large influence on the properties of low-dimensional materials. Here, we examine the change of the band gap (Eg), the optical absorption coefficient (OAC), the refractive index (RI), and the optical conductivity of a monolayer MoSe2 (ML) with respect to the variation in the external electric field strength. Our results, based on a density-functional theory (DFT) calculation, exhibit an increase in the band gap when the electric field is turned on. However, we are witnessing a remarkable decrease in Eg for electric field strengths exceeding +/- 0.7 Va-1. Further, we obtained a great correlation between the external electric field and the OAC. On the other hand, we have established that the light polarization perpendicular to the plane of the ML-MoSe2 shifts the position of the OAC peak to shorter wavelengths, and leads to a split of OAC peak located at 110 nm. We have also achieved that the external electric field reduces the optical conductivity of the ML-MoSe2 in the UV region. That effect is found to be more pronounced when the MoSe2 nanosheet is subjected to a 001-polarized incident light and positive field strengths. However, the presence of an external electric field generally improves the optical conductivity in the visible region. Lastly, in the case of 001-polarization of the incident wave, we found that the RI shrinks in the UV region when the electric field is turned on. By contrast, the application of an external electric field tends to improve the refractive index in the visible region.