Abstract: Carbon-doped Al N films were prepared on Si(100) and quartz substrates by radio frequency(RF)dual-target reactive co-sputtering to investigate the effect of carbon concentration on the optical properties of Al Nfilms. It was found that the carbon concentration in the prepared co-sputtering Al N films was lower than that of sin-gle Al target sputtering Al N films. The carbon concentration in the films decreased from 2.10% to 1.91% as the RFdischarge power of the graphite target increased from 20 to 40 W, compared to 3.50% while sputtering with a singlealuminum target. This was due to the fact that when the graphite target is added, the nitrogen gas in the vacuumchamber participates in the graphite target discharge generating CN radicals, which in turn react with the residualcarbon oxide gas in the background vacuum to form volatile and stable CNO radicals, thus reducing the density ofcarbon oxide density on the film growing surface and leading to a reduction in the carbon concentration of the depos-ited film. The Al N films were characterized by using X-ray diffraction analysis, X-ray photoelectron spectroscopyand ultraviolet-near infrared spectroscopy. The results show that the carbon concentration in the film has an obvi-ous effect on its optical properties. A single aluminum target sputtering resulted in higher carbon concentration(3.50%), the Al N film has a smaller optical band gap of 3.90 e V; while co-sputtering with the graphite target powerof 20, 25, 30, 40 W, the carbon concentration is reduced to 2.10%, 1.81%, 1.83%, 1.91% respectively, the Al Nfilms had larger optical band gap of 4.85, 4.91, 4.88, 4.81 e V. The increase in optical band gap is caused by the car-bon impurity reduction in the films deposited by co-sputtering.