Nonlinear optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition

The real and imaginary parts of third-order nonlinear susceptibility x(3) have been measured for silicon nanocrystals embedded in SiO2 matrix, formed by high temperature annealing of SiOx films prepared by plasma-enhanced chemical vapor deposition. Measurements have been performed using a femtosecond Ti-sapphire laser at 813 nm using the Z-scan technique with maximum peak intensities up to 2E10 W/cm2. The real part of x(3) shows positive nonlinearity for all samples. Intensity-dependent nonlinear absorption is observed and attributed to two-photon absorption processes. The absolute value of x(3) is on the order of 1029 esu and shows a systematic increase as the silicon nanocrystalline size decreases. This is due to quantum confinement effects.