Photoconductivity and photoluminescence of a-Si : H and a-SixC1-x : H films prepared by glow discharge or R.F sputtering have been studied. For a-Si : H sputtered films, the photoconductivity is greatly increased with R.F power, substrate temperature and can be compared to values obtained for glow discharge films. The addition of a low carbon content (< 10 %) does not affect the photoconductivity but a higher content greatly decreases it. In conclusion, we deduced that the existence of a high 1.2 eV photoluminescence peak is a necessary condition to obtain a good photoconductivity.