First-principles study of the electronic structures and optical properties of g-ZnO/CdX (X = S, Se, Te) van der Waals heterostructures.

The stability, electronic structures and optical properties of g-ZnO/CdX (X = S, Se, Te) heterostructures are studied by density functional theory. It is found that the stable monolayers spacing of the corresponding heterostructure decreases with the increase of the X atomic radius in the CdX monolayers. The constructed g-ZnO/CdX heterostructures all belong to direct band gap, 2.12 eV, 2.09 eV and 1.99 eV, respectively. Electrostatic potential results show that the two monolayers form an internal electric field at the heterostructure interface, and can inhibit the recombination of photogenerated electron hole pairs, and effectively extend the carrier lifetime. Charge density difference analysis shows that charge redistribution mainly occurs in the interfacial region. The optical properties show that the absorption of g-ZnO in the visible range is achieved by heterostructure. In general, with the smallest band gap and the strongest built-in electric field, g-ZnO/CdTe could have the best carrier separation efficiency. And the optical property analysis proves that the g-ZnO/CdTe heterostructure system has the highest utilization ratio of visible light. The above results show that the electronic structure and optical properties of g-ZnO/CdTe heterostructure are the best, and it can be inferred that this heterostructure will be the most beneficial to improve the photocatalytic activity of g-ZnO, providing a new direction for its application in the field of photocatalysis.