The nc Si∶H thin films were prepared by hotfilament vapor deposition.The effect of gas pressure,-high H2 dilution and substrate-to-filament distance on deposition rate,the formation and structure of nc-Si∶H films was systematically studied.The structure of nc-Si∶H was determined using Raman scattering and X-ray diffraction.The temperature distribution was calculated;the travel of radicals evaporated from the filament and the gas-phase reaction were discussed in detail.The results were in agreement with the measurement.