Relationship between the structure and the optical and electrical properties of reactively sputtered carbon nitride films

Amorphous carbon nitride films (CNx) were grown by reactive radio-frequency (RF) magnetron sputtering of a high-purity graphite target in argon/nitrogen (Ar/N2) gas mixture. The total discharge pressure was 1 Pa and the total nitrogen partial pressure (NPP) in plasma was between 0 and 0.10%. The properties of films were determined using X-ray photoelectron spectroscopy (XPS), infrared absorption, and transmission spectroscopy. The electrical resistivity of films was studied as a function of temperature between 110 and 573 K. The optical gap varies from 0.30 to 0.7 eV in the range of the studied N content in good agreement with the resistivity measurements. The two types of conduction mechanisms can be interpreted basis on the band structure model of the ππ electrons in a disordered carbon with the presence of localized states.