Nitrogen Doping Effect in Cu 4 O 3 Thin Films Fabricated by Radio Frequency Magnetron Sputtering

N‐doped Cu 4 O 3 thin films are deposited by radio frequency magnetron sputtering in an ambient of Ar, O 2 , and N 2 using a pure Cu target. The structural, electrical, and optical properties are investigated systematically with the variation of N 2 gas flow during deposition. Results reveal that N 2 flow rate has a strong influence on both the composition and functional properties of the resulting Cu 4 O 3 films. X‐ray diffraction (XRD) and Raman spectroscopy indicate the formation of the single phase of N‐doped Cu 4 O 3 at a low N 2 flow rate of up to 4.3 sccm. From the optical absorption analyses, both undoped and N‐doped Cu 4 O 3 films show a direct forbidden transition at E g  = 1.34–1.44 eV. All the undoped and N‐doped Cu 4 O 3 thin films show p‐type conductivity, and N‐doped Cu 4 O 3 shows lower resistivity on the order of 10 1 –10 2  Ω cm. These results indicate clearly that N‐doped Cu 4 O 3 is a very promising material for the absorber in low‐cost thin film solar cells.