[en] Polymorphous silicon carbon (pm-SiC:H) thin films have been prepared from the decomposition of SiH₄-CH₄-H₂ mixtures at low temperature (200 deg. C) 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 (I) 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