Amorphous carbon nitride (a-CNx) thin films have been synthesised by three different deposition techniques in an Ar/N-2 gas mixture and have been deposited by varying the percentage of nitrogen gas in the mixture (i.e. the N-2/Ar + N-2 ratio) from 0 to 10%. The variation of the electrical conductivity and the gap values of the deposited films versus the N-2/Ar + N-2 ratio were investigated in relation with their local microstructure. Film composition was analysed using Raman spectroscopy and optical transmission experiments. The observed variation of electrical conductivity and optical properties are attributed to the changes in the atomic bonding structures, which were induced by N incorporation, increasing both the sp(2) carbon content and their relative disorder. The low N content samples seem to be an interesting material to produce films with interesting properties for optoelectronic applications considering the facility to control the gas composition as a key parameter. (C) 2008 Elsevier B.V. All rights reserved.