Films minces à base de Si nanostructuré pour des cellules ...

samples from atmosphere since this shoulder lies at the (TO 3 ) Si−O peak position.
The inset of gure 4.4 shows that the spectra recorded in the normal incidence
also exhibits a similar behaviour with annealing. There is a shift of the TO mode
between 843-864 cm −1 indicating a rearrangement of the Si and N atoms. The TO
peak after CA shows an increased width which is attributed to an overlapping of
TO Si−N with (TO 3 ) Si−O modes due to oxidation.
(b) X-Ray Diraction
tel-00916300, version 1 - 10 Dec 2013
The XRD spectra obtained from as-grown, STA and CA SRSN samples (n 1.95eV =2.44)
are shown in gure 4.5. A peak around 28° corresponding to Si (111) plane appears
after CA (1h-1100°C), indicating the formation of Si nanocrystals.
The XRD spectra of the as-grown
and STA samples are similar with a
broad peak between 20-30°. This may
be attributed to the presence of amorphous
Si clusters that begin to form even
during the growth process, due to the Si
Figure 4.5: XRD spectra of as-grown and
annealed SRSN samples grown by reactive
sputtering.
excess (n 1.95eV ∼ 2.44) and high temperature
of deposition (500°C). The investigations
parallely conducted in our
team on thinner samples (100-200 nm)
revealed that despite a Si excess in SiN x
materials, the formation of Si nanocrystals
were not observed for samples with
n 1.95eV < 2.4 [Debieu 12]. The observation
of nanocrystals in our case may
suggest that we are at a value of refractive index close to the threshold to form
nanocrystals. The peak around 56° in all the spectra is a contribution from the Si
substrate, as mentioned earlier.
(c) Raman spectroscopy
The formation of Si-np was also analyzed by Raman spectroscopy on SRSN layers
(n 1.95eV ∼ 2.44) grown on fused silica substrate after subjecting to STA and CA
treatments. The Raman spectra recorded by varying the laser power density between
0.14 and 0.7 MW/cm 2 are presented in gure 4.6. The Stokes shift in eV is marked
on the upper scale in the gure. The inset shows the PL spectra obtained in the
Raman set-up using a higher power density of 1.4 MW/cm 2 .
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