Al-doped ZnO films deposited on a slightly reduced buffer layer by reactive dc unbalanced magnetron sputtering

•Al-doped ZnO (AZO) films with AZO buffer layers were deposited.•Reactive dc unbalance magnetron sputtering with impedance control was used.•Insertion of a buffer layer can lead to a lower resistivity.•Insertion of a buffer layer improved the crystallinity of AZO films.

Al-doped ZnO (AZO) films were deposited on a fused silica glass substrate by reactive dc unbalanced magnetron sputtering using a Zn–Al (Al: 3.6 at.%) alloy target with an impedance control system. A very thin slightly reduced AZO buffer layer was inserted between the glass substrate and AZO films. For the AZO films deposited at 200 °C, the lowest resistivity in the absence of the buffer layer was 8.0 × 10− 4 Ω cm, whereas this was reduced to 5.9 × 10− 4 Ω cm after introducing a 5-nm-thick buffer layer. The transmittance for all the films was above 80% in the visible region. The effects of the buffer layer were analysed and discussed in detail. It is found that the insertion of the buffer layer can improve the crystallinity of the AZO film.