Raman spectroscopy experiments correlated with infrared absorption, optical
transmission and photothermal deflection spectroscopy ones are used to
investigate in detail the short-range-order (SRO) and
intermediate-range-order (IRO) in hydrogenated amorphous silicon (a-Si:H)
films elaborated at high rates (~15 Å/s) by radiofrequency
magnetron sputtering with various hydrogen dilution percentage (5 to
20%), leading to different hydrogen-related microstructure and content.
The analysis of the transverse optic (TO)- and transverse acoustic (TA)-like
modes of the Raman spectra indicates that both, the SRO and IRO are more
strongly dependent on the nature of hydrogen bonding configurations, namely
the relative proportion of polyhydride Si-H2 and (Si-H2)n
complexes and/or clustered monohydride (Si-H)n groups incorporated in
the films, rather than on the total bonded hydrogen content. The increase
observed in the line width of the TO- and TA-like modes are well correlated
with that of the disorder parameter E0, also called Urbach edge
parameter, which is related to the exponential absorption from the valence
band tails states distribution. Moreover, the analysis of the optical
transmission data clearly evidences that the dispersion energy Ed and
the static refractive index n0 are also maximum for films having the
lowest value of E0, suggesting that they exhibit the highest mean
coordination number and compactness respectively, consistent with better SRO
and IRO.