The paper reports results obtained from optical spectrophotometry complemented with data from FTIR, Raman scattering and XRD measurements to characterize hydrogenated silicon (Si:H) thin films deposited by PECVD deposition from silane – argon plasma diluted with hydrogen. The dispersive optical properties and microstructure have been determined as a function of the hydrogen dilution which has been found to result in an inhomogeneous growth during which the material evolves from amorphous Si:H to microcrystalline Si:H. Porosity originating from microvoids has been discovered and calculated using effective medium approximations. Bruggeman effective medium approximation (BEMA) has been used to calculate volume fractions of microvoids and amorphous and crystalline phase.
The effects of deposition conditions (especially lateral position against target during deposition and deposition
temperature) on optical properties and structure are presented. The X-ray diffraction (XRD) analysis showed that all
the films were polycrystalline with hexagonal structure and preferred orientation in  direction perpendicular to
the substrate surface. Micro-structure properties as crystallite size and micro-strains were not too influenced by
deposition conditions and values of crystallites were evaluated in tens of nanometers and micro-strains were about 10<sup>-2</sup>.
Film thicknesses obtained from transmittance spectra decreased more than two times with increased lateral position of
the samples against the target. Dispersion of the spectral refractive index was observed depending on the sample position
in deposition chamber. Smaller dispersion was observed in series containing more redundant oxygen in their structure.