Electronic and optical properties tuned by strain and external electric field of g-ZnO/2H-TiS2 van der Waals heterostructures

The electronic and optical properties of g-ZnO/2H-TiS2 van der Waals heterostructures are investigated by density functional theory. A promising out-of-plane polarization spontaneously induced by 2H-TiS2 is found for the g-ZnO monolayer, which can be significantly tuned in a wide range of 9.929 mu C/cm to 33.271 mu C/cm by the in-plane strain. A type-II band alignment and an indirect band gap of 0.05 eV are presented in the stable g-ZnO/2H-TiS2 heterostructure. Although the type of band alignment keeps steady, the band gap value can be tuned by strain, which results in the transformation of the g-ZnO/2H-TiS2 heterostructure from semiconductor to metal. Furthermore, the g-ZnO/2H-TiS2 heterostructure exhibits extraordinary absorption properties in the visible and ultraviolet regions. The absorption peaks in visible region present red shift under the compressive strain and blue shift under the tension. In addition, the out-of-plane polarization modulation is observed in g-ZnO/2H-TiS2 heterostructures under the external electric field. For the positive electric field, the out-of-plane polarization and band gap increase significantly. While for the negative electric field, both out-of-plane and band gap are obviously reduced. Our investigation might give some theoretical guidances for the development and application of the g-ZnO/2H-TiS2 heterostructure in sensors, ferroelectric, and optoelectronic devices.