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

- Peak (3) and (c): 1.8-1.95 eV
Dierent names are given for the three peaks in 100(3.5/5) and 50(3.5/5) ML
since the origin of these three peaks in both the cases may be dierent. It can be
seen that the position of peak (c) is sometimes the same as peak (2) or sometimes
as peak (3) leading to confusions on the origin of this emission. Hence, further
investigations were made in an attempt to understand the origin of PL emission
4.10.1 Role of defects in the matrix
In order to see the inuence of SRSN sublayers on the emission of peaks, 50(3.5/3.5)
SRSN/SiO 2 MLs were grown and subjected to STA, CA and FG annealing. The
tel-00916300, version 1 - 10 Dec 2013
PL spectra obtained from SRSO/SRSN MLs can be compared with SRSN/SiO 2
and SRSO/SiO 2 MLs in order to identify the contribution of SRSO, SRSN and
SiO 2 sublayers independently. Figure 4.43 compares the PL spectra obtained from
SRSO/SiO 2 , SRSO/SRSN and SRSN/SiO 2 MLs with 50(3.5/3.5) conguration after
STA and CA. It can be noticed from the spectra of CA annealed samples that the
SRSN/SiO 2 ML exhibits a weak PL around 1.9 eV while that from SRSO/SRSN
ML is quenched as demonstrated before (ref. Fig. 4.25). This PL peak appears
in a region usually related to the optical transitions in the SiO 2 matrix due to the
presence of defects [Gourbilleau 09, Delachat 09].
The lower part of the gure 4.43
shows the PL spectra recorded from
STA MLs. It can be noted that both
SRSN/SiO 2 and SRSO/SiO 2 emit PL at
the same peak position (around 1.9 eV),
the latter being very weak. This indicates
that besides SiO 2 , SRSN sublayers
also contribute to emission around
1.9 eV in SRSN/SiO 2 ML. The PL intensity
of SRSN/SiO 2 increases with annealing
temperature while the peak position
remains xed at 1.9 eV (See inset
of Fig. 4.43). From gure 4.40 one can
remark that that this peak around 1.9
eV is not seen in 50(3.5/5) ML, while
in 100(3.5/5) it is signicant. Moreover,
even under N 2 annealed STA samples,
this peak was noticed with increasing
Figure 4.43: PL spectra from 50(3.5/3.5)
SRSO/SRSN, SRSO/SiO 2 and SRSN/SiO 2
MLs after STA and CA treatments.
129