Two sets of hydrogenated amorphous silicon carbide (a-SiCx:H) thin films were grown on glass and c-Si substrates by Plasma enhanced chemical vapor deposition (PECVD) technique at pressures of 0.5 and 0.1 Torr. The influence of the pressure on the distribution of thicknesses, refractive indices at 632.8 nm and optical gaps from the edge to the center of the bottom electrode of PECVD system is examined by transmission, single wavelength ellipsometry and Fourier transform infrared spectroscopy. A recently introduced optimization method considering some prior knowledge of common optical properties of amorphous semiconductor thin films have been applied to the optical transmission spectra for estimating thickness and optical constants of a-SiCx:H thin films at hand. In addition, spectral characteristics of these constants are analyzed by fitting experimental data through Forouhi-Bloomer, Tauc-Lorentz and single Lorentz oscillator models. The retrieved results show that while the thicknesses and optical band gaps are decreasing towards the center of the electrode, refractive index is slightly increasing in that direction. Chemical processes occurring during the film deposition are discussed. These distributions of the film constants have been interpreted as due to the carbon incorporation whose efficiency might increase towards the edge of the electrode corresponding to a longer residence time of carbon radicals. (C) 2003 Elsevier Science B.V. All rights reserved.