Comparative study of the nonlinear optical properties of Si nanocrystals fabricated by e‐beam evaporation, PECVD or LPCVD

The nonlinear optical properties of silicon nanocrystals (Si-nc) embedded in oxide matrices have been studied in samples obtained by three different technological process: e-beam evaporation, plasma enhanced or low pressure chemical vapor deposition (PECVD and LPCVD, respectively). Z -scan measurements were performed in all the samples at 1064 nm by using ns-pulses of a Nd:YAG laser. Similar nonlinear refractive index was found in the three systems, while differences in the nonlinear absorption were found as a function of the deposition method. The nonlinear results have been evaluated in terms of the crystalline and amorphous fractions from Raman scattering and photoluminescence (PL) measurements. While PL measurements show a emission spectrum similar for all the samples, Raman spectra reveal a sizeably different Si crystalline/amorphous ratio, depending on the deposition method. Therefore, the interface between the SiO2 matrix and Si-nc plays a crucial role in determining the nonlinear optical response of the Si-nc rich layers. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)