On Nanometer Ordering in thin Amorphous Hydrogenated Silicon

We investigated thin films of amorphous hydrogenated silicon (a-Si:H) deposited by PECVD under increasingdilutions of silane plasma by hydrogen. We found out that under increasing additional hydrogen at the depositions, thin filmsobtain less hydrogen bonded to silicon. The optical band gap energies determined from UV Vis transmittance and reflectancespectra were found to be increasing function of the dilution. We deduce that optical band gaps expanse due to the decreasingdimensions of silicon nanocrystals. They were calculated to be of 2 – 4 nm which proves the medium-range order in a-Si:H.