Nitrogen Doping Effect in Cu₄O₃ Thin Films Fabricated by Radio Frequency Magnetron Sputtering

N-doped Cu₄O₃ thin films are deposited by radio frequency magnetron sputtering in an ambient of Ar, O₂, and N₂ using a pure Cu target. The structural, electrical, and optical properties are investigated systematically with the variation of N₂ gas flow during deposition. Results reveal that N₂ flow rate has a strong influence on both the composition and functional properties of the resulting Cu₄O₃ films. X-ray diffraction (XRD) and Raman spectroscopy indicate the formation of the single phase of N-doped Cu₄O₃ at a low N₂ flow rate of up to 4.3 sccm. From the optical absorption analyses, both undoped and N-doped Cu₄O₃ films show a direct forbidden transition at E_g = 1.34–1.44 eV. All the undoped and N-doped Cu₄O₃ thin films show p-type conductivity, and N-doped Cu₄O₃ shows lower resistivity on the order of 10¹–10² Ω cm. These results indicate clearly that N-doped Cu₄O₃ is a very promising material for the absorber in low-cost thin film solar cells.