Characterization and optoelectronic properties of sol–gel-derived CuFeO2 thin films

Abstract In this study, CuFeO 2 thin films were deposited onto quartz substrates using a sol–gel and a two-step annealing process. The sol–gel-derived films were annealed at 500 °C for 1 h in air and then annealed at 600 to 800 °C for 2 h in N 2 . X-ray diffraction patterns showed that the annealed sol–gel-derived films were CuO and CuFe 2 O 4 phases in air annealing. When the films were annealed at 600 °C in N 2 , an additional CuFeO 2 phase was detected. As the annealing temperature increased above 650 °C in N 2 , a single CuFeO 2 phase was obtained. The binding energies of Cu-2p 3/2 , Fe-2p 3/2 , and O-1s were 932.5 ± 0.1 eV, 710.3 ± 0.2 eV and 530.0 ± 0.1 eV for CuFeO 2 thin films. The chemical composition of CuFeO 2 thin films was close to its stoichiometry, which was determined by X-ray photoelectron spectroscopy. Thermodynamic calculations can explain the formation of the CuFeO 2 phase in this study. The optical bandgap of the CuFeO 2 thin films was 3.05 eV, which is invariant with the annealing temperature in N 2 . The p-type characteristics of CuFeO 2 thin films were confirmed by positive Hall coefficients and Seebeck coefficients. The electrical conductivities of CuFeO 2 thin films were 0.28 S cm − 1 and 0.36 S cm − 1 during annealing at 650 °C and 700 °C, respectively, in N 2 . The corresponding carrier concentrations were 1.2 × 10 18 cm − 3 (650 °C) and 5.3 × 10 18 cm − 3 (700 °C). The activation energies for hole conduction were 140 meV (650 °C) and 110 meV (700 °C). These results demonstrate that sol–gel processing is a feasible preparation method for delafossite CuFeO 2 thin films.