A comparative study on the dielectric functions of isolated Si nanocrystals and densely-stacked Si nanocrystal layer embedded in SiO2 synthesized with Si ion implantation

Abstract

Both isolated Si nanocrystals (nc-Si) dispersedly distributed in a SiO2 matrix and densely stacked nc-Si layers embedded

in SiO2 have been synthesized with the ion implantation technique followed by high temperature annealing. The

dielectric functions of the isolated nc-Si and densely-stacked nc-Si layer embedded in SiO2 have been determined with

spectroscopic ellipsometry (SE) in the photon energy range of 1.1-5 eV. The dielectric functions of these two different Si

nanostructures were successfully extracted from the SE fitting based on a multi-layer fitting model that takes into

account the distribution of nc-Si in SiO2 and a five phase model (i.e., air/SiO2 layer/densely-stacked nc-Si layer/SiO2

layer/Si), respectively. The dielectric spectra of isolated nc-Si distributed in SiO2 present a two-peak structure, while the

dielectric spectra of densely-stacked nc-Si layer show a single broad peak, being similar to that of amorphous Si. The

dielectric functions of these two Si nanostructures both show significant suppressions as compared with bulk crystalline

Si. However, it has been observed that the densely stacked nc-Si layer exhibits a more significant suppression in the

dielectric spectra than the isolated nc-Si dispersedly embedded in SiO2. This is probably related to the two factors: (i) the

nc-Si size (~3 nm) of the densely stacked nc-Si layer is smaller than that (~4.5 nm) of the isolated nc-Si embedded in

SiO2 matrix, and (ii) the densely stacked nc-Si layer has an amorphous phase.