Amorphous to microcrystalline phase transition in hydrogenated silicon (Si:H) is realized separately with the variations of substrate temperature and hydrogen dilution. The Raman spectroscopy reveals structural transformations and marks the transition. It occurs at similar to450degreesC with 10% silane concentration, whereas that is noted at 25degreesC with a silane concentration of 4.5%. The material evolved in the transition region is a well-developed amorphous matrix containing a small fraction (similar to12%) of crystallites. A uniform distribution of small (similar to100 Angstrom) crystallites in the films is observed by transmission electron microscopy. The transition material is photosensitive. (C) 2002 Elsevier Science B.V. All rights reserved.