Amorphous intrinsic silicon carbide (a-SiCx:H(i)) films and amorphous silicon carbonitride (SiCxNy:H) films have been deposited by plasma enhanced chemical vapor deposition from CH4/SiH4/(N-2) plasma on n-type (1.5 Omega cm) crystalline silicon (c-Si). These films have evidenced excellent surface passivation properties with a best result for the surface recombination velocity S-eff approximate to 2-3 cm s(-1) for amorphous SiCxNy:H films, which is the lowest reported value for n-type c-Si with resistivity of 1.5 Omega cm so far. IR transmission spectroscopy was performed to get more detailed information about the structural composition of the films. Integrated absorption of the bands typical for Si-C and Si-N bonds reveals that N-2 addition to the plasma leads to nitrogen incorporation into the films but also enhances the incorporation of carbon. From IR analysis it is found that the characteristic minimum of the S-eff for a certain CH2/SiH4 gas flow ratio is not correlated with the bulk properties of the amorphous films. However, first analysis of injection level dependent lifetime measurements indicates that the minimum in S-eff is related to good interface properties of the silicon carbon alloy deposited in the composition range of x approximate to 0.2. (C) 2003 Elsevier B.V. All rights reserved.