Optics of Si/SiO2 superlattices: Application to Raman scattering and photoluminescence measurements

Abstract

A quantitative model of a Si/SiO2 superlattice (SL) is developed and applied to Raman and photoluminescence (PL) measurements. By analyzing the experimental reflection spectra of Si/SiO2 SLs on Si and Al substrates, we obtained optical parameters of amorphous Si layers with thickness below 4 nm. Both refractive index and extinction coefficient are found to decrease with Si-layer thickness, and this behavior reflects interaction of the Si network and the oxide surrounding. Interference-induced modification of Raman scattering and PL is quantitatively studied for Si/SiO2 SLs on Si and Al substrates, and the developed optical model describes well all observed features. PL spectra of the Si/SiO2 SLs are found to change under Ar+-laser irradiation, and this effect of laser annealing becomes stronger for thinner Si layers. For 1-nm-thick Si layers, a prolonged laser exposure decreases the PL intensity at 550 nm by a factor of 10 and red-shifts its maximum by about 50 nm, which indicates essential reorganization of the network under laser irradiation.