Microstructural, optical, and electrical properties of Ni–Al co-doped ZnO films prepared by DC magnetron sputtering

Graphical abstract: - Highlights: • Ni–Al co-doped ZnO (NiAl:ZnO) composite thin films were deposited by DC magnetron sputtering at room temperature. • All films showed a highly preferential (0 0 2) c-axis orientation. • XPS revealed the presence of metallic Ni, NiO, and Ni₂O₃ states, and Ni atoms were successfully doped in the NiAl:ZnO films. • NiAl:ZnO (3 wt% Ni) film showed the lowest electrical resistivity of 2.59 × 10⁻³ Ω cm. • Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni. - Abstract: Ni–Al co-doped ZnO (NiAl:ZnO) films with fixed Al content at 2 wt% and different Ni contents (2.5, 3, and 5 wt%) were deposited by DC magnetron sputtering in an argon atmosphere at room temperature. X-ray diffraction revealed that all films showed a highly preferential (0 0 2) c-axis orientation. XPS revealed the presence of metallic Ni, NiO, and Ni₂O₃ states, and Ni atoms were successfully doped in NiAl:ZnO films, which did not result in a change in ZnO crystal structure and orientation. The electrical resistivity of NiAl:ZnO film was decreased to 2.59 × 10⁻³ Ω cm at a Ni doping concentration of 3 wt% compared with undoped Al-doped ZnO film (5.58 × 10⁻³ Ω cm). The mean optical transmittance in the visible range was greater than 80% for all films. Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni, attributed to the Burstein–Moss shift due to the increase of carrier concentration