Effect of Cu addition on the properties of the RF magnetron-sputtered Cu 2 O thin films

Radio frequency (RF) magnetron sputtering was used to fabricate Cu-doped Cu2O thin using a gas mixture containing 80% Ar and 20% N2 at room temperature. The Cu2O ceramics containing different concentrations of Cu powder (1–7 wt%) were considered to be the sputtering targets. A highly dense Cu-doped Cu2O target was essential to obtain excellent quality Cu2O films; this target can be obtained via the hot-pressing process because the low melting point (1084.6 °C) of Cu allows enhanced densification of the Cu2O target through a liquid-phase wetting mechanism. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) were performed to characterize the Cu2O film microstructure. Our results denoted that Cu doping enhances the densification and increases the grain size of the Cu2O films. Further, the crystal structures of the films changed from CuO and Cu4O3 to Cu2O when the Cu doping concentration increased from 1 to 7 wt%. A dense and well-defined columnar morphology can be observed when TEM was used to observe the film microstructure. Subsequently, the electrical and optical properties of the Cu2O thin films were evaluated at different Cu concentrations. The electrical resistivity of the Cu2O films became 8.6 Ω·cm when the Cu doping concentration was 7 wt%, corresponding to a carrier density of 9.8 × 1016 cm−3 and a mobility of 7.5 cm2/Vs. Furthermore, the optical transmission of the Cu2O films doped with Cu was greater than 60%. The band gaps of the films ranged from 2.32 to 2.54 eV depending on the copper oxide phases present in the films.