Effect of lack of oxygen on optical and electrical properties of RF magnetron sputtering deposited CuFeO2−x thin films

Abstract

Delafossite CuFeO[Formula: see text] thin films were fabricated on quartz substrate using radio-frequency sputtering deposition under low O2 flow ratios from 9% to 0% at room temperature. The as-deposited films were in amorphous phase and crystallized into rhombohedral 3R (R3m) delafossite structure after post annealing at 900[Formula: see text]C for 2 h in flowing N2 atmosphere. SEM images showed that the films were composed of nano-sized crystallized grains, thin film composed of smoother surface and higher oxygen content was obtained under higher oxygen percentage in sputtering gas. The optical transmission spectra of these films were studied in the wavelength range 200–1500 nm and the results revealed a narrowing trend of direct bandgap from 3.09 eV to 2.98 eV with the decrease of oxygen flow ratio during deposition. All of the post-annealed CuFeO[Formula: see text] thin films exhibited p-type conductivity and linear ohmic contact feature with Cu electrodes. The carrier concentration of thin films increased from [Formula: see text] to [Formula: see text] whereas the carrier mobility decreased from [Formula: see text] to [Formula: see text] as the oxygen flow ratio reduced from 9% to 0%. The ability of controlling compound composition enables tuning of carrier concentration and mobility in CuFeO[Formula: see text] and offering essential technical basis in engineering photoelectronic devices.