Abstract
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.