Magnetron sputtering process of carbon-doped α-Fe₂O₃ thin films for photoelectrochemical water splitting

Highlights: • Carbon-doped α-Fe₂O₃ films were synthesized by sputtering process. • The parameter of C-doped α-Fe₂O₃ was RF power of graphite target. • The photoelectrochemical characteristics of C-doped α-Fe₂O₃ films were investigated. - Abstract: Thin films of α-Fe₂O₃ doped with carbon have been fabricated on F-doped SnO₂ glass substrate by magnetron sputtering process via DC power on the pure Fe target (99.99%) combined with RF power on the pure graphite target (99.99%). The influences of RF power (0, 40, 80 and 120 W) on optical, structural and photoelectrochemical (PEC) characteristics have been investigated. The as-obtained samples after annealing in Ar ambient were analyzed by scanning electron microscopy, X-ray diffraction (XRD), Raman spectra, UV–visible spectra and electrochemical analysis. After annealing, all samples revealed only hematite characteristics in XRD pattern and Raman spectra. Thickness of annealed thin films was ∼350 nm measured via SEM cross-section image. The optical band gap and carrier concentration of samples were in the range of 2.13–2.16 eV and 6.28 × 10¹⁷ to 3.11 × 10¹⁸ cm⁻³, respectively. Based upon our observations, the 4.56 at.% carbon-doped α-Fe₂O₃ thin film deposited via 80 W RF power has a better PEC response with photocurrent density of ∼1.18 mA/cm² at 0.6 V vs. SCE. This value was about three times higher than the un-doped film (0 W of RF power, reference sample). Observed higher photocurrent density was likely due to a suitable carbon-doping concentration causing a higher carrier concentration