Experimental determination of the nanocrystalline volume fraction in silicon thin films from Raman spectroscopy

Abstract

The effect of crystallite sizes L smaller than 100 nm on the integrated Raman cross section Σ_c of the transverse optical (TO) mode of fcc silicon was studied experimentally in fully nanocrystallized thin films. The Σ_c/Σ_a (amorphous) ratio of this mode is shown to be 1 up to L=30 Å, and to decay exponentially down to 0.1 at larger L. A systematic procedure taking into account both this effect and the experimental optical absorption coefficient α_exp at the excitation wavelength is then proposed for the determination of the crystalline volume fraction in mixed phase (amorphous/nanocrystalline) silicon systems by Raman measurements.