Bonding structure and optical properties of a-CNx:H films deposited in CH4–NH3 system

Hydrogenated amorphous carbon nitride (a-CNx:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) in CH4–NH3 system. The chemical composition and bonding configuration were investigated by XPS and FTIR. The results indicated that both sp2CN and sp3CN bonds generally increased with the increase of the nitrogen concentration, and the N atoms bonded to C atoms through CN, CN and CN bonds. Remarkably, for FTIR spectra, two peaks (2125 and 2200 cm−1) were obviously observed, corresponding to CN bond which was found to predominantly exist in the isonitrile structure. As more nitrogen atoms were incorporated, the optical band gap was found to vary from 1.8 to 2.5 eV. Finally, the conduction mechanisms were discussed at low and high temperature, respectively.