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

ˆ the hydrogen reacts with the oxygen species in the plasma which are sputtered
from SiO 2 target, leading to the growth of a Si-rich suboxide at the substrate.
Consequently, n 1.95eV increases with r H .
(b) Fourier transform infrared spectroscopy
tel-00916300, version 1 - 10 Dec 2013
Figure 3.6 shows the FTIR spectra of the as-grown SRSO samples with varying r H
in Brewster incidence and in the inset, the normal incidence spectra. The TO 3 peak
is normalized to unity as in the previous analysis. The variation of LO 3 and TO 3
peak positions with regard to r H are also shown in the inset.
It can be seen from the
Brewster incidence spectra that
the LO 3 peak intensity decreases
with increasing r H . At
r H = 57%, the LO 3 peak becomes
the least intense, and
a peak around 1107 cm −1 is
observed. We also notice an
increase in disorder with r H
from the increasing intensity of
LO 4 -TO 4 in Brewtser incidence
Figure 3.6: FTIR spectra - Eect of hydrogen rate
on the SRSO lm structure.
spectra and TO 4 peak in normal
incidence spectra. Traces
of Si-H are seen in all the samples
from the Brewster incidence
spectra.
The decreasing LO 3 intensity can be attributed to the increase in Si excess and
therefore agglomeration of Si-np leading to lower number of interfaces as discussed
in previous section. The increase in Si excess with r H also leads to an increase in
structural disorder thereby enhancing the disorder induced modes. Similar eect
with increasing Si excess by increasing RF power density on the target has been
observed in our earlier reports [Hijazi 09a]. The huge decrease of LO 3 intensity
and a higher enhancement of the LO 4 -TO 4 mode due to Si excess may be a possible
reason for the appearance of the peak around 1107 cm −1 . This peak position has also
been reported as interstitial oxygen in Si substrates [Kaiser 56, Borghesi 91, Veve 96]
and at Si/SiO 2 interfaces [Niu 07]. It has been proposed that interstitial oxygen in
Si may have a structure similar to fused silica with Si-O-Si bond angle 100 ° which
would result in a TO Si−O stretching vibration around 1107 cm −1 [Kaiser 56] and
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