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

(a) As recorded.
(b) Normalized to pattern number.
Figure 3.22: PL spectra to see the inuence of SiO 2 barrier thickness by investigating
(a) as recorded spectra and, (b) spectra normalized to pattern number.
tel-00916300, version 1 - 10 Dec 2013
gure 3.22b, the PL spectra are normalized to the pattern number. A monotonous
trend of emission intensity with t SiO2 is observed considering MLs with 4 nm thick
SRSO sublayers. In the case of t SiO2 = 1.5 nm, the Si diusion between two consecutive
SRSO sublayers are not prevented, leading to the overgrowth of Si-np. This
might explain the low PL emission from 90(4/1.5) ML.
The PL spectra in both gures show that the emission peaks from 70(4/3) and
90(4/1.5) MLs are positioned at the same energy while a blueshift is observed with
10 nm SiO 2 sublayers. In order to conrm this, the curves of MLs with 4 nm thick
SRSO sublayers were tted using gaussian functions (Tab. 3.9).
Sample Peak (1) eV Peak (2) eV
36(4/10) 1.42 1.61
70(4/3) 1.40 1.57
90(4/1.5) 1.40 1.56
Table 3.9: Peak positions of MLs with 4 nm
thick SRSO sublayer.
All the curves are composed of two
peaks: peak (1) and peak (2). The
blueshift of the peaks with increasing
t SiO2 is noticed. As seen from the structural
analysis in section 3.8.2, it is clear
that there is some interaction between
two consecutive SRSO for lower barrier
thicknesses, forming bigger Si-np. In
the case of 10 nm barrier thickness, the
SRSO layers are well separated and and the formation of Si-np is restricted only
to the SRSO sublayers due to higher connement oered by t SiO2 . As a result, the
formed Si-np are smaller leading to a blueshift of the PL intensity. In addition to all
these microstructural eects, the emission might be inuenced also by geometrical
and optical eects which will be investigated in chapter 5.
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