Evidence of localized amorphous silicon clustering from Raman depth-probing of silicon nanocrystals in fused silica

Silicon nanocrystals (Si-nc) and amorphous silicon (alpha-Si) produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Information regarding the Raman signature of the alpha-Si phonon excitation was extracted from Raman depth-probing measurements using the phenomenological phonon confinement model. The spectral deconvolution of the Raman measurements recorded at different laser focusing depths takes into account both the Si-nc size variation and the Si-nc spatial distribution within the sample. The phonon peak associated with a-Si around 470 cm(-1) is greatest for in-sample laser focusing, indicating that the formation of amorphous silicon is more important in the region containing a high concentration of silicon excess, where large Si-nc are located. As also observed for Si-nc systems prepared by SiO(x) layer deposition, this result demonstrates the presence of a-Si in high excess Si implanted Si-nc systems.