Electronic and Optical Properties of 2D-TMD/Janus Heterostructures Under the Influence of an Electric Field: First-Principles Calculations

This work presents the results of a theoretical investigation of the electronic and optical properties of van der Waals Janus nanoheterostructures MoS₂/SeMoS and MoSe₂/SMoSe, carried out within the framework of density functional theory (DFT) using the generalized gradient approximation (GGA-PBE) together with the Grimme-D3 dispersion correction. The calculated band structures show that both heterostructures possess an indirect bandgap whose magnitude is highly sensitive to an external electric field. In the MoS₂–SeMoS system, increasing the applied field leads to a gradual narrowing of the bandgap and a transition to a metallic state at approximately 75 V, whereas in MoSe₂–SMoSe, the bandgap first increases (up to 20 V) and then decreases, indicating a nonlinear field-dependent behavior. Analysis of the dielectric function reveals an enhancement of the static dielectric permittivity and a red shift in the absorption spectra with increasing field strength, which can be attributed to charge redistribution and an increased contribution from ionic polarizability. These results demonstrate the possibility of effectively controlling the bandgap width, polarizability, and optical response of Janus nanoheterostructures using an external electric field. This opens up promising prospects for their application in tunable photodetectors, light modulators, valleytronic components, and next-generation optoelectronic systems.