Structural and chemical features of silicon nanocrystallites in nanocrystalline hydrogenated silicon thin films

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited on Si wafers at room temperature by plasma-enhanced chemical vapor deposition (PECVD): a mixture of SiH4 and H-2 was introduced into the evacuated reaction chamber. The films were postdeposition annealed at temperatures of 400-1100 degrees C. The silicon nanocrystallites (nc-Si) in the films range from similar to 4.0 to similar to 8.0 nm in size, depending on the hydrogen flow rates as well as the annealing conditions. The relative fractions of the Si-H-3, Si-H-2, and Si-H bonds in the nc-Si:H films varied sensitively with the heat-treatment conditions. Local radial distribution function (RDF) analysis of the films was performed by using selected area electron diffraction methods. A model for the nanostructure of the nc-Si:H films was suggested to take into account the variation in the size and chemical bonds of the nanocrystallites as well as the amorphous matrix.