Linear and Nonlinear Optical Properties of Plasma Enhanced Chemical-Vapour Deposition Grown Silicon Nanocrystals

We provide a systematic study on the linear and nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma-enhanced chemical vapour deposition (PECVD). Linear optical properties, namely absorption, emission and refractive indices are reported. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ(3) of Si-nc are measured by the Z-scan method. Closed aperture Z-scan reveals a positive nonlinearity for all the samples. From the open aperture measurements, nonlinear absorption coefficients are evaluated and attributed to two-photon absorption. Absolute values of χ(3) are in the order of 10-9 esu and show systematic correlation with the Si-nc size, due to quantum confinement related effects. A correlation has been made between χ(3), nanocrystalline size, linear refractive index and optical band gap.