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Microstructure related optical characterization of technologically relevant hydrogenated silicon thin films

We report results obtained from measurements of UV Vis, FTIR and Raman spectra carried out on a series of silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from silane diluted with hydrogen. Spectral refractive indices, extinction coefficients, optical band gap energies, hydrogen content, the microstructure factor, and grain size were determined as a function of the hydrogen dilution. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (µc-Si:H). With increasing dilution Si:H films become mixed-phase materials with changing volume fractions of crystalline and amorphous phases and voids. The optical band gap energies were determined from transmittance spectra. The grain size was determined from Raman spectra and the contribution of small and large grains was detected.