Optical losses and absorption cross-section of silicon nanocrystals

Si-rich silicon oxide and SiO2 (SRSO)/SiO2 multilayer (ML) samples were grown by reactive magnetron sputtering and then annealed at high temperature to induce the formation of Si-nc with mean size of 3–4 nm and density of about 3.5×1018 cm−3 as deduced from high resolution TEM micrographs. Refractive index and thickness have been determined by m-line measurements, which have shown a birefringence of about 1.5% due to the ML structure. Rib-loaded waveguides have been fabricated to measure propagation losses in the visible–infrared range. The analysis of the different contributions to optical losses such as Mie scattering and scattering due to waveguide roughness has allowed us to isolate the contribution due to the absorption losses and thus to extract the absorption cross-section at different wavelengths. Values of about 3.5×10−18 cm2 have been found at 830 nm, increasing with decreasing of the wavelength.