Effects of silicon nanocrystallite density on the Raman-scattering spectra of silicon quantum dot superlattices

Abstract

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-SiO x /a-SiO 2 ordered arrays by reactive RF magnetron co-sputtering. The composition of the SiO, (1<x<2) ordered arrays has been controlled by varying the coverage percentage of the silicon target. On high temperature annealing, phase separation occurs into nano-crystalline Si and amorphous SiO 2 . The Raman scattering spectra presented in this study suggest a dot size-dependent peak below 520 cm -1 (I nc ) and an inter-dot spacing-dependent shoulder between 495 and 500 cm -1 (I s ). 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 (J nc /I s ,) and conductivity of SiQD superlattices with various compositions of the SiO x are presented.