Polymorphous silicon carbon (pm-SiC:H) thin films have been prepared from the decomposition of SiH4-CH4-H-2 mixtures at low temperature (200 IQ by plasma-enhanced chemical vapour deposition (PECVD). The optical and microstructural properties of the films were studied by spectroscopic ellipsometry and Raman spectroscopy. The SiH4/CH4 flow rate ratio is demonstrated as a key deposition parameter for optimizing the electroluminescence of PIN diodes incorporating this material for the intrinsic (1) layer. Diodes with rectification ratios above 106 were realized by using the optimized materials. Electroluminescence spectra, centred at 1.4 eV, were obtained by applying a DC voltage lower than 4 V, which make these devices interesting for optoelectronic applications. (c) 2007 Elsevier B.V. All rights reserved.