The electronic and optical properties of hydrogenated amorphous carbon (a-C: H) and nitrogenated : hydrogenated amorphous carbon (a-C: H: N), deposited using inductively coupled plasma enhanced chemical vapour deposition (ICPECVD) and helicon wave excited plasma enhanced chemical vapour deposition (HWPECVD) are discussed in this thesis. The design and the implementation of the helicon wave excited plasma system is also presented. The capacitance voltage (C-V) characteristics of heterojunctions formed by depositing a-C: H: N on Si, show that almost ideal interface behaviour can be accomplished using ICPECVD for optimised plasma conditions. The highest frequency response, known to date for a-C, 13MHz, is also reported. The photoluminescence (PL) studies are carried out to investigate the influence of nitrogen in a-C: H: N. The nitrogen and the optical band gap dependencies of PL indicated the existence of N associated recombination centres. A twin recombination mechanism at localised tails and N associated centres is suggested to describe the observed behaviour. The capability of selective energy transitions in a helicon wave plasma as predicted theoretically is successfully demonstrated for N2 plasma. The passivation of high power electronic devices and the electron field emission are presented as potential areas where a-C: H and a-C: H: N perform successfully