Amorphous hydrogenated carbon nitride thin films have been grown by plasma decomposition of a feedstock of CH4 and N2. In the films with higher nitrogen concentration, the infrared absorption spectra are dominated by NH2 modes and give strong evidence of a polymeric structure. The optical absorption and photoluminescence spectra show that nitrogen incorporation decreases the bandgap and increases the structural order of these thin films. The undoped material is an insulator with resistivities up to 1015Q cm, but when doped with iron, it becomes a p-type degenerate semiconductor.