Silicon nanostructures based on silicon quantum dots (SiQDs) in a silicon dielectric are being investigated for application to Si based tandem cells. The main challenge for such a structure is to obtain sufficient carrier mobility and hence a reasonable conductivity. It is believed that the conductivity of such novel SiQDs embedded in a silicon dielectric matrix is controlled by the close spacing of the SiQDs. In this study we grew a-SiOx/a-SiO2 ordered arrays by reactive RF magnetron co-sputtering. The composition of the SiOx (12. The Raman scattering spectra presented in this study suggest a dot size-dependent peak below 520 cm-1 (Inc) and an inter-dot spacing-dependent shoulder between 495 and 500 cm-1(Is). The correlation between crystalline silicon density and ratio of the relative integrated intensity of SiQDs and its shoulder bands are presented. The size of the SiQDs is also confirmed by structural analysis through transmission electron microscopy (TEM) and X-ray diffraction (XRD). Initial analysis of the relationship between the relative integrated intensity (Inc/Is) and conductivity of SiQD superlattices with various compositions of the SiOx are presented.
Superlattices of silicon nanocrystals or quantum dots (QDs) are fabricated by depositing alternating layers of
stoichiometric and sub-stoichiometric silicon nitride by dual-mode PECVD and subsequent high temperature annealing.
NH3, SiH4 and Ar are used as processing gases. The formation of QDs is monitored for varying annealing temperatures
using TEM and GI-XRD. Samples composed of 50 bi-layers are grown under the same conditions and annealed for two
hours at temperatures ranging between 600 and 1150°C. A 50 bi-layer superlattice structure of silicon nanocrystals with
an estimated average grain size of approximately 4 nm was achieved at 1000°C. The use of FTIR spectroscopy as a
complementary technique for verifying the formation of silicon nanocrystals in a nitride matrix is investigated. The IR absorbance spectra for samples containing silicon nanocrystals show a distinct shoulder at 1080 cm-1 corresponding to
the Si-O-Si stretching mode possibly due to oxidation. Preliminary evidence is also presented showing the possible
formation of α-Si3N4 nanocrystals at 1100 and 1150°C.