Band Gap Width Control by Cu Intercalation Into ZrSe2

The CuxZrSe2 intercalation single crystals have been synthesized and studied in a concentration range of x = 0–0.3, in which the semiconductor-metal transition was observed. The evolution of the electronic structure of CuxZrSe2 as a function of the copper content has been studied experimentally using the XPS and XAS methods. The obtained results indicate the gradual shift of the Fermi level with increasing copper content, which does not allow the metal–insulator transition to be associated with charge transfer to the conduction band. This transition is associated with the formation of the covalent bond between copper and the nearest selenium atoms and of the p–d hybridized states inside the Zr 4d/Se 4p band gap. First-principle calculations were performed in order to obtain a theoretical description of the density of states near the Fermi level and confirm this conclusion.