Tailoring of electrical properties of Cu2O thin films fabricated by oxygen injection after argon plasma reduction of CuO films

Abstract

Cu2O thin films with tailored electrical properties were produced by 25 s plasma reduction of CuO films and immediate oxidation under oxygen flows of 0, 3, 6, 9, 12, 15, and 18 sccm. CuO target films were easily prepared by the dip-coating method and annealing at 400 °C. CuO was transformed to Cu2O by employing an argon plasma treatment devised in our laboratory. Cu2O was produced as the only crystalline phase detected, and the films exhibited smooth surfaces with roughness around 5 nm. All films presented high reflectance in the fundamental absorption region (30%) and high transmittance in the transparency region of Cu2O (65%). The good optical behavior permitted the accurate calculation of optical constants by fitting reflectance and transmittance to an optical model designed with the help of Film Wizard™ software. Variations with oxygen injection were detected for the components of the dielectric function, index of refraction, and absorption coefficient. More importantly, the electrical properties of Cu2O showed a clear dependence on O2 injection. Even though resistivity was on average 80 Ω∙cm, hole mobility varied in the span of 0.75–3.2 cm2/V s, and hole density in the range of 1016–1017/cm3. Upon storage in open-air conditions, the mobility of Cu2O films was increased to 3.8 cm2/V s. The Cu2O films produced show similar quality to those obtained by a sputtering deposition method. However, simpler equipment was employed. The plasma method studied is promising for fast mass production of Cu2O thin films.