Ab initio investigation of vertical strain and electric field effects on electronic and optical properties of GeO2/MoSi2N4 van der Waals heterostructure

By constructing two-dimensional van der Waals heterostructures, the physical properties of monolayer materials can be significantly enhanced. In this study, we have proposed a van der Waals heterostructure composed of MoSi2N4 and GeO2 monolayers. Using first principles based on density functional theory, we systematically investigated its electronic and optical properties under varying vertical pressure and external electric field (E). The results obtained showed that GeO2 and MoSi2N4 monolayers are direct semiconductors. The GeO2/MoSi2N4 vdW heterostructure exhibits a type II band alignment with a direct bandgap value of 1.962 eV. Under an external electric field (E), the bandgap varies linearly with the field, and a strong electric field induces a semiconductor-to-metal transition. We observed similar behavior when applying biaxial strain. The effect of the electric field on the bandgap of heterostructures is marginally stronger than that of the vertical strain. However, it should be noted that the type II band arrangement is well-preserved in the GeO2/MoSi2N4 vdW heterostructure in all the biaxial strain cases studied under different electric field values. The optical absorption of the heterostructure exhibits anisotropic behavior, and it is enhanced in the ultraviolet region. Our results can serve as a reference for future experimental studies of the GeO2/MoSi2N4 vdW heterostructure concerning potential applications in optoelectronic and spintronic devices. Graphical abstract