Optical and structural characterization of inhomogeneities in a-Si:H TO μc-Si transition

The a-Si:H films with different thickness and microstructure have been deposited with rf-PECVD using a plasma of silane diluted with hydrogen. The structure and optical analysis were carried out by X-ray diffraction, UV–VIS and Raman spectroscopy. Spectral refractive indices, optical energy band gaps, extinction coefficients, phases ratio and grain size were determined as a function of the hydrogen dilution (R = H2/SiH4). Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to micro-crystalline hydrogenated silicon (μc-Si:H). XRD analysis indicated that films with R = 0 and R = 20 were amorphous and homogeneous, while films with R = 40 and higher were micro-crystalline consisting medium range ordered silicon hydride (Si4H) and μc-Si phases with different size of crystallites, which was confirmed also by Raman spectroscopy.