The microstructural dependence of the opto-electronic properties of nitrogenated hydrogenated amorphous carbon thin films

The microstructural properties of nitrogenated hydrogenated amorphous carbon (a-C:H:N) thin films deposited using a chemical vapour deposition system are analysed in order to evaluate their impact on the opto-electronic properties. Electron energy loss spectroscopy is used to reconstruct a joint density of states (JDOS) for the a:C:H:N films and thus used to examine the microstructure. Information obtained from optical absorption is then used to confirm the JDOS. Using this JDOS we attempt to predict the variation expected in the electronic conduction as a function of nitrogen content. The electrical data obtained for the a:C:H:N thin films appear to be bulk controlled as opposed to metal contact dominated for films that are deposited on the driven electrode and are more diamond-like in character. The bulk electronic properties at high fields are fitted to different types of conduction behaviour in order to obtain the best fits to the data. From this study it is observed that a Poole–Frenkel type fit is best for films that have a diamond-like structure. For the films that have a polymeric structure which are deposited on the earthed electrode the conductivities are very much lower, and consistent with the lower defect densities observed in the microstructural study. It is possible that the conduction in these films are Schottky barrier controlled.