Characterization of amorphous hydrogenated carbon nitride films prepared by plasma-enhanced chemical vapor deposition using a helical resonator discharge

Amorphous hydrogenated carbon nitride thin films (a-CN_x:H) have been prepared by plasma-enhanced chemical vapor deposition of N₂ and CH₄ gases using a helical resonator discharge. The structural and optical properties of the deposited a-CN_x:H films have been systematically studied as a function of the substrate temperature and radio frequency (rf) substrate bias. The chemical structure and elemental composition of the a-CN_x:H films were characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The optical properties of the films were evaluated using transmission ultraviolet-visible spectroscopy. The morphology of the films was investigated by scanning electron microscopy and atomic force microscopy. The FT-IR and XPS studies demonstrate the presence of carbon-nitrogen bonds with hydrogenated components in the films. The film composition ratio N/C was found to vary from 0.127 to 0.213 depending on the deposition conditions. The Raman spectra, showing the G and D bands, indicate that the a-CN_x:H films have a graphitic structure. It can be found that the optical band-gap E_g of a-CN_x:H films is associated with graphitic clusters, while the decrease in E_g is correlated with an increase in the size and number of graphitic clusters. Combining the results of Raman and optical measurements, it can be concluded that a progressive graphitization of the films occurs with increasing the substrate temperature and rf substrate bias power, corresponding to bias voltage.