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

tel-00916300, version 1 - 10 Dec 2013
The thicknesses of the SRSO and
SRSN sublayers are seen to be 3.7 nm
and 5.1 nm respectively, conrming the
pattern thickness of 8.8 nm deduced
from XRR technique. The presence of
Si nanocrystals are witnessed only in the
SRSO sublayers and most of them were
restricted to the 3.7 nm sublayer thickness,
coherent with average size estimation
from XRD. However, nanocrystals
that show overgrowth in both the width
and the height were also observed as
shown in this gure. The presence of
oversized Si nanocrystal could be the
consequence of high temperature and
time applied on a Si-rich (SRSO, SRSN)
lm during the annealing process. It can
Figure 4.24: HR-TEM image of CA
100(3.5/5) SRSO/SRSN ML. The arrows indicate
the possible exodiusion paths.
also be noticed that there are regular darker regions (arrows in Fig. 4.24) in the
SRSO sublayers that lie along a line. This can be attributed to the path of gas
exodiusion during annealing, as suspected to be one of the reason for surface modications
in the optical microscopy analysis of the CA sample (ref. Fig. 4.21).
4.5.7 Optical properties
(a) Photoluminescence
The PL spectra of as-grown and CA samples of 100(3.5/5) ML are shown in gure
4.25. The SRSO/SRSN as-grown sample shows PL emission contrary to SRSO/SiO 2
samples which did not show emission before annealing. This emission from the asgrown
SRSO/SRSN ML achieved by the replacement of SiO 2 by SRSN sublayer
suggests that the SRSO sublayer is emitting and the presence of defects in SiO 2
might have quenched the PL in SRSO/SiO 2 MLs.
The as-grown PL spectrum can be seen to contain three peaks centered around
1.41 eV (peak 1), 1.62 eV (peak 2) and 1.88 eV (peak 3). This suggests the presence of
dierent emission centers in the material such as defects or amorphous Si-np in SRSO
and/or SRSN sublayers. The position of peaks (1 and 2) might be ascribed to the
electron-hole recombination in the Si-np within the frame of QCE [Kanemitsu 97,
Ternon 04a, Gourbilleau 09]. Peak (3) closely relates to 1.9eV value reported for
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