Due to their specific properties, silicon nanocrystals (Si-nc) embedded in dielectric matrix have recently attracted much interest for their use in silicon-based devices. The fabrication of these nanostructures is fully compatible with the existing technologies. However, in order to develop efficient devices, the properties of the Si-nc and their host matrix have to be strictly controlled. In this work, Si-nc embedded in silicon carbide or silicon nitride matrix have been fabricated and characterized to provide a better understanding of the structural, optical and electrical properties. These two matrices received our attention because of their intermediate gap between silicon and silicon dioxide which is expected to give improved properties for electrical components. Two synthesis techniques have been used: the nucleation/growth of Si-nc on a-Si0,8C0,2 thin films by low pressure chemical vapor deposition (LPCVD), and the deposition by pulsed plasma enhanced chemical vapor deposition (PPECVD) of Si-rich a-SiNx alloys followed by high temperature annealing. During the results interpretation, a particular attention was paid to the surface/interface effects as well as the influence of the matrix. After analyzing and controlling the deposition parameters of a-SiCx:H alloys by PECVD, we showed that the nucleation/growth of Si-nc on a-Si0,8C0,2 surface by LPCVD is appropriate because of the high Si content in the carbide matrix. We obtained Si-nc densities higher than 1012 cm-2, even for low growth time or SiH4 flow rates. These results show the feasibility of such structure. A detailed study of the Si-nc/silicon nitride couple was then realized using a large range of diagnostics. First, it was shown that the size of Si-nc can be estimated by Raman spectroscopy. We also explained the process of Si-nc formation during annealing and suggested a model for the structure of Si-nc/a-Si3N4 interfaces from the deconvolution of the XPS spectra. Then, the optical properties of Si-nc were determined by spectroscopic ellipsometry and UV-Vis spectroscopy. The increase of the gap, broadening and weakening of the dielectric constants, and increase of the absorption coefficient at low energy suggest a confinement effect in the Si-nc. Time-resolved photoluminescence measurements indicated that the use of a nitride matrix would not be appropriate to the study of Si-nc optical emission, due to the large number of radiative and non-radiative defects in the matrix and at the interfaces. Finally, charge carriers transport mechanisms through the nanocomposite layer were determined through current-voltage measurements. Because the percolation threshold is reached, the film embedding Si-nc behaves as polycristalline Si with a low amount of Si dangling bonds. A photoconduction effect is observed which gives interesting works in sight.
