Effects of oxygen partial pressure on the structural and optical properties of undoped and Cu-doped ZnO thin films prepared by magnetron co-sputtering

Undoped and Cu-doped zinc oxide (ZnO:Cu) films were deposited on glass substrates by magnetron sputtering at different oxygen partial pressures p_o. Microstructure, surface morphology, resistivity, and optical properties were systematically investigated. The results show that lower p_o can degrade the crystallinity, and reduce the band gap. Undoped ZnO films are not obviously influenced by p_o, especially at high oxygen pressure. In contrast, ZnO:Cu thin films are remarkably affected by p_o. This work suggests that oxygen vacancies play an important role in modifying properties and allows us to accurately modulate the band gap of the ZnO-based films.