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

volume of SRSN in the material and was seen only in 100(3.5/5) ML (Ref. Fig.
4.35b) or 50(3.5/t SRSN>5nm ) after gaussian curve tting (not shown here). In order
to verify the inuence of annealing under FG and SRSN volume on this PL peak
intensity, SRSN/SiO 2 ML was also subjected to FG annealing (Fig. 4.44). The
SRSN sublayer thickness in this ML is lower (=3.5 nm) than in SRSO/SRSN MLs
investigated above in section 4.6 and still the peak around 1.9 eV is present.
tel-00916300, version 1 - 10 Dec 2013
Figure 4.44: PL spectra obtained from FG
annealed 50(3.5/5) SRSN/SiO 2 .
In both gures 4.43 and 4.44, 1.9
eV peak is present in SRSN/SiO 2 MLs
despite the two dierent annealing processes
employed. In the case of N 2
annealing, since the SiO 2 defects are
mostly passivated after CA, we can reasonably
assume that the dominant contribution
of this emission is from SRSN
sublayers which also to emit in the same
energy range as SiO 2 . In the case of FG
annealed samples the dominant contribution
of luminescence comes from defects
in SiO 2 , since the temperature is
lower for defect passivation. These observations help us to attribute the peak (3) of
SRSO/SRSN PL spectra to be the contribution of SRSN sublayer.
The presence of nanocrystals were found neither in XRD spectra of SRSN/SiO 2
[Nalini 12] nor in the TEM images of SRSO/SRSN thereby indicating the emission
from SRSN sublayer is not from Si-np. It can be seen that there is a blueshift in
the central peak position from 1.57 eV after STA to 1.75 eV after FG annealing in
50(3.5/5) SRSO/SRSN ML (Ref. Fig. 4.39a), whereas for the two dierent annealing
processes under N 2 or FG ow employed on SRSN/SiO 2 MLs there is no change in
the peak intensity and the position remains xed around 1.9 eV. Theoretical model
has predicted that for a given defect, the peak position is xed and cannot be
controlled with ease [Kim 05]. This peak position around 1.9 eV can therefore be
ascribed to the defects in SRSN sublayers.
Besides these defect related PL, it can be said that in a SRSO based ML, replacing
SiO 2 by SRSN sublayers favours Si-np emission also, at a reduced thermal budget
(STA in SRSO/SRSN versus CA in SRSO/SiO 2 MLs). Thus, SRSN sublayers contribute
signicantly towards emission around 1.9 eV (peak 3) and between 1.5-1.7
eV (peak 2) due to defects in the matrix, and by favouring the Si-np formation
respectively.
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