  The outstanding demonstration of quantum confinement in Si nanocrystals (Si
NC) in a SiC matrix requires the fabrication of Si NC with a narrow size
distribution. It is understood without controversy that this fabrication is a
difficult exercise and that a multilayer (ML) structure is suitable for such
fabrication only in a narrow parameter range. This parameter range is sought by
varying both the stoichiometric SiC barrier thickness and the Si-rich SiC well
thickness between 3 and 9 nm and comparing them to single layers (SL). The
samples processed for this investigation were deposited by plasma-enhanced
chemical vapor deposition (PECVD) and subsequently subjected to thermal
annealing at 1000-1100${\deg}$C for crystal formation. Bulk information about
the entire sample area and depth were obtained by structural and optical
characterization methods: information about the mean Si NC size was determined
from grazing incidence X-ray diffraction (GIXRD) measurements.
Fourier-transform infrared spectroscopy (FTIR) was applied to gain insight into
the structure of the Si-C network, and spectrophotometry measurements were
performed to investigate the absorption coefficient and to estimate the bandgap
$E_{04}$. All measurements showed that the influence of the ML structure on the
Si NC size, on the Si-C network and on the absorption properties is subordinate
to the influence of the overall Si content in the samples, which we identified
as the key parameter for the structural and optical properties. We attribute
this behavior to interdiffusion of the barrier and well layers. Because the
produced Si NC are within the target size range of 2-4 nm for all layer
thickness variations, we propose to use the Si content to adjust the Si NC size
in future experiments.
