Characterization of transparent conductive delafossite-CuCr1−xO2 films

In this study, the CuCr1−xO2 films with x = 0.00–0.25 were prepared on a quartz substrate by sol–gel processing. The films were first deposited onto a quartz substrate by spin-coating. The specimens were annealed at 500 °C in air for 1 h and post-annealed in N2 at 700 °C for 2 h. As the films were post-annealed in N2, a pure delafossite-CuCrO2 phase appeared in the CuCr1−xO2 films below x = 0.20. However, an additional CuO phase appeared at x = 0.25. The pure delafossite-CuCrO2 phase can exist within x ≤ 0.20 in CuCr1−xO2 films. The binding energies of Cu-2p3/2 and Cr-2p3/2 in the CuCr1−xO2 films with the pure delafossite-CuCrO2 phase were 932.1 ± 0.2 eV and 576.0 ± 0.2 eV, respectively. The surface exhibited elongated grain features when the pure delafossite-CuCrO2 phase was present in the CuCr1−xO2 films. The maximum transmittance of the CuCr1−xO2 films with the pure delafossite-CuCrO2 phase was approximately 80%, which moved toward the visible region with the increasing x-value. The film absorption edges were observed at 400 nm, which were sharper with the increasing x-value. The optical bandgaps of CuCr1−xO2 films with the pure delafossite-CuCrO2 phase were approximately 3.0 eV. The electrical conductivity of CuCr1−xO2 films with the pure delafossite-CuCrO2 phase was 1.1 × 10−3 S cm−1 (x = 0.00), and increased to 0.16 S cm−1 (x = 0.20). The corresponding carrier concentration of CuCr1−xO2 films with the pure delafossite-CuCrO2 phase was 2.8 × 1014 cm−3 (x = 0.00), and markedly increased to 1.8 × 1016 cm−3 (x = 0.20). The Cr-deficient condition in delafossite-CuCrO2 films enhances film electrical conductivity and carrier concentration, but retains the filmʹs high-visible transparency.