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

(a) Fourier transform infrared spectroscopy
tel-00916300, version 1 - 10 Dec 2013
Figure 3.11 shows the FTIR spectra before
and after annealing recorded using
Brewster incidence. The inset in this gure
shows an enlarged view of the Si-H
peak variations with annealing.
It can be seen that the LO 3 peak intensity
gradually increases with increasing
annealing temperatures. Considering
the eect of time, for a given temperature
1000°C (1min-1000°C and 1h-
1000°C) there is no signicant change in
the LO 3 peak intensity whereas there is
a drastic increase when the sample is annealed
at 1h-1100°C.
This trend represents a gradual evolution towards the phase separation process
Figure 3.11: Eect of annealing on the
FTIR spectra in Brewster incidence.
upon annealing. A gaussian curve tting performed on these spectra indicated
a reduction in the peak widths of LO 3 and TO 3 peaks with increasing annealing
temperatures. Such reduction in the peak width with increasing annealing treatment
has also been observed in [Morales-Sanchez 08] and these changes are attributed
to the phase separation processes. In addition, we also notice an increase of the
LO 4 −TO 4 mode upon annealing. This indicates the disorder in the matrix due to
high Si excess. It can be seen that the Si-H peak appears only in the as-grown
sample. The desorption of hydrogen occurs with increasing annealing temperatures
leading to a disappearance of this peak.
(b) Raman spectroscopy
The evolution of Si-np formation between as-grown and 1h-1100°C annealed SRSO-
P15 sample as reected by FTIR spectra is conrmed through Raman spectroscopy
following the procedure detailed in chapter 2 under section 2.4.4 (Fig. 3.12).
It can be seen that the as-grown sample shows a broad peak centered at 480
cm −1 , which decreases in intensity after 1h-1100°C annealing with the appearance
of a new peak at 517.6 cm −1 . The Raman spectrum of the as-grown layer shows
dominant features of amorphous Si, since SiO 2 is reported to have a very low scattering
cross section [Kanzawa 96, Khriachtchev 99]. This conrms the formation
of amorphous Si-np in the as-grown sample as indicated by ∼24 at.% of agglomerated
Si estimated using ellipsometry (Bruggeman) method (Ref. Tab. 3.6).
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