Study on NiO:Zn²⁺ films fabricated through dc magnetron reactive sputtering: substrate temperature-dependent microstructure pattern, optical and electrical properties

Nickel oxide (NiO) films have potential applications in optical coatings, ultraviolet detectors, gas sensors and perovskite solar cells. The great improvement in electrical conduction is still critical for NiO films so far. NiO films are usually p-type conductive because of the native Ni vacancies and interstitials O. These native point defects make n-type NiO difficult to prepare. Even that, n-type NiO films with improved electrical conduction still need to be prepared for n-NiO-based heterojunction devices. Herein the face-centered cubic NiO:Zn²⁺ films are magnetron reactively sputtered on the glass substrates at different substrate temperatures (T_sub). The introduction of Zn²⁺ to NiO leads to the transition in conduction from p to n at 400 °C T_sub. The films are almost improved in crystallization with increase in T_sub, thereby reducing the point defect content i.e. the free carrier concentration. The resulting films are also improved in optical transmittance with increase in T_sub. The film's optical energy gap is tunable in the range of 3.6 eV through 3.8 eV with T_sub. (paper)