A series of investigations were performed to study the influence of the substrate temperature on the structure and properties of silicon thin films. Substrate temperature was varied in the wide range of 35-200 degreesC. It has been shown that the films grown below 60 degreesC exhibit an unusual structural behavior. A sharp TO phonon peak at 520 cm(-1) was detected in Raman spectra, which is associated with the crystalline structure. In contrast to these results, the same samples do not show any crystallite-related peak by X-ray diffraction and their optoelectronic properties (dark conductivity, activation energy and subgap absorption spectra) show amorphous features. A similar discrepancy was observed for a hydrogen dilution ratio (r(H) = ([SiH4] + [H-2])/[SiH4]) series of samples deposited at 60 degreesC. Hydrogen dilution ratio was varied from 25 to 170. It seems that at low substrate temperature a parameter window exists where the silicon thin films can be grown with the properties combining both crystalline and amorphous behavior. (C) 2003 Elsevier B.V. All rights reserved.