Hydrogenated intrinsic Si (Si:H) thin films were deposited by a plasma-enhanced chemical vapor deposition technique, and the effect of the SiH4 flow rate ([SiH4]) and hydrogen dilution ratio (R) on the crystalline phase transition was studied using Raman spectroscopy and high-resolution transmission electron microscopy. The crystalline volume fraction (X-c) was strongly affected by [SiH4] as well as R, and higher X-c could be achieved by using a lower [SiH4] at the same R. The dependence of phase transition on the crystallinity of the under-lying layer was also investigated by depositing Si:H films on various substrates. To evaluate the effects of [SiH4] and R on the quality of amorphous-Si:H (a-Si:H) films, etch rates and absorption coefficients were obtained by an H-2-plasma etching process and UV-Vis spectrophotometry, respectively. Even under the deposition condition resulting in a-Si:H films, the deposition rate decreased by a factor of 3 to 4.6, and the film density considerably increased as R increased from 4 to 19. On the other hand, the absorption coefficient very slightly decreased with R. The presence of microcrystalline Si: H could be observed only from the samples deposited with R > 19 when the film was deposited on amorphous substrate. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592428] All rights reserved.