Amorphous Si: H and Si: F: H films, doped as well as non-doped, have been prepared both by glow-discharge (GD) and reactive-sputtering (SP) methods, and their structural properties have been investigated systematically through X-ray diffraction, Raman scattering, EPMA and ir transmission measurements. Optical and electrical properties are discussed in relation with the contents of Ar, doped element (P), bonded H and dangling bonds and with film structure. It has also been demonstrated that high RF power deposition results in crystallization of Si: H films, independent of whether doped or non-doped, and their structure has been characterized as a mixed phase, consisting microcrystals (100-A size) embedded in amorphous network.