Nanostructural and Optical Features of nc-Si:H Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition Techniques

Abstract

The nanostructural and optical features of hydrogenated nanocrystalline silicon (nc-Si:H) thin films, which were prepared by plasma enhanced chemical vapor deposition (PECVD), were investigated as a function of deposition conditions. It was found that the crystallite size varied with the relative fraction of Si-H3 bonds in the films, [ ] eger n n n H Si H Si int 3 1 3 / ] [ = = ∑ − − , which was sensitively related with the flow rate of SiH4 reaction gas. The silicon nanocrystallites in the films enlarged from ~2.0 to ~8.0 nm in their size with increasing gas flow rate, while the PL emission energy varied from 2.5 to 1.8 eV; the relative fractions of the Si-H3, Si-H2, and Si-H bonds in the amorphous matrix were also varied sensitively with the SiH4 flow rate. A model for the nanostructure of the nc-Si:H films was suggested to discribe the variations in the size and chemical bonds of the nanocrystallites as well as the amorphous matrix depending on the deposition conditions.