Comparative study of the nonlinear optical properties of Si nanocrystals fabricated by ebeam evaporation, PECVD or LPCVD
A. Martínez,1 S. Hernández,1 P. Pellegrino,1 O. Jambois,1 M. Grün,2 P. Miska,2 H. Rinnert, 2 V.
Izquierdo-Roca,3 J.M. Fedeli,4 and B. Garrido1
MIND-IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i Franquès 1,
08028 Barcelona, Spain.
2
Laboratoire de Physique des Matériaux, UMR CNRS 7556, Nancy University, BP 239,
54506 Vandoeuvre-lès-Nancy Cedex, France.
3
M-2E/XaRMAE/IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i
Franquès 1, 08028 Barcelona, Spain.
4
CEA, LETI, Minatec, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
1
Silicon nanocrystals (Si-nc) embedded in oxide matrices have been proposed as active material
for nonlinear photonic applications, as their nonlinear optical properties were found to be larger
than the ones in silica or Si. For their fabrication, several approaches have been widely
employed, such as ion implantation, evaporation, plasma enhanced or low pressure chemical
vapor deposition (PECVD and LPCVD, respectively). However, the different technological
steps strongly affect the precipitation of Si-aggregates and their surrounding medium, affecting
their structural, and both linear and nonlinear optical properties. Here we present a comparison
of the nonlinear optical properties of Si-nc under ns excitation pulses for materials produced by
three different techniques.
Si-rich oxides were deposited onto silica substrates either by LPCVD, PECVD or e-beam
thermal evaporation, and subsequently annealed at high temperatures in order to precipitate the
nanostructures. Energy filtered transmission microscopy was used to determine the size and
distribution of Si-nc, finding a mean size of ~5 nm in all the samples. The crystalline and
amorphous fractions were estimated from the integrated intensity of Raman spectra performed
in cross-section configuration. The nonlinear response was determined at 1064 nm by z-scan
experiments and using ns-pulses of a Nd:YAG laser. While a similar nonlinear refractive index
was found in all the samples, differences in the nonlinear absorption were found as a function of
the deposition method. Furthermore, the nonlinear response was analyzed by varying the
duration of the laser pulses, finding different trends for each sample. The nonlinear response
will be discussed and presented in correlation with the nanostructure of the Si precipitates and
their linear optical response.