The effect of the terminating bonds on the electronic properties of sputtered carbon nitride thin films

Amorphous carbon nitride films (a-CNx) were grown by reactive radio-frequency magnetron sputtering of a graphite target in an argon/nitrogen gas mixture. The total discharge pressure was 1 Pa and the total nitrogen partial pressure (NPP) in plasma was varied between 0 and 100%. The correlation between the microstructure changes, the optoelectronic properties and the internal stress has been investigated in order to prevent the limiting role of the terminating bonds on the electronic properties of the a-CNx films, and to determine the range of the nitrogen content improving these properties. The analysis of the results reveals that below 3%, the nitrogen incorporation induces an increase in the density of π-bonds, which promotes the enhancement of the conductivity and the reduction of the optical gap. With increasing NPP ratio up to 6%, the formation of terminating bonds within the network reduces the connectivity of the graphitic network, decreasing the conductivity. For higher N content, the reaction of the bonds terminating with water can increase the compressive stress, leading to spontaneous delamination of films.