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

摘要

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-H_3 bonds in the films, [Si-H_3]/∑ from n=1 to 3 of [Si-H_n]_(n=integer), which was sensitively related with the flow rate of SiH_4 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-H_3, Si-H_2, and Si-H bonds in the amorphous matrix were also varied sensitively with the SiH_4 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.