The network disorder of a-Si1-xCx: H films containing carbon concentrations below 20 at.% has been studied by means of Raman spectroscopy and photoluminescence (PL) measurements. Two different radiations were employed to excite these materials, one higher than the optical gap and strongly absorbed (488 nm), the other near to the optical gap and weakly absorbed (647.1 nm). When excited with strongly absorbed radiation, the frequency and width of TO mode have a large redshift and broadening relative to the weakly absorbed radiation, while the position and width of PL peak have a blueshift plus broadening. The variations in probed depth together with the significant differences observed in the Raman spectra and PL spectra indicate the existence of two types of inhomogeneities: a highly disordered thin layer near free surface and gap fluctuations due to spatial variations of compositions in the bulk. The above results indicate that Raman and PL characteristics at different radiations can be used to explore the spatial variations of materials. (C) 2002 Elsevier Science B.V. All rights reserved.