Ellipsometric study of carbon nitride films deposited by DC-magnetron sputtering

We report the optical properties of a carbon nitride (CNx) film as a function of nitrogen concentration (N/C) of the deposited film. As nitrogen concentration is increased (N/C ratio) in a CNx film, the refractive index and band gap also increase. The real and imaginary parts, n and k (refractive index and extinction coefficient) of the complex refraction index of carbon nitride films were determined by spectroscopic ellipsometry (SE) in the photon energy range from 1.8eV up to 4.8eV. Both n and k reveal a significant variation with deposition conditions. A detailed ellipsometric analysis showed that the refractive index varies from 1.8 to 2.05 at different nitrogen concentrations. The optical band gap of the deposited films was situated in the range 1.34eV-1.58eV.