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

tel-00916300, version 1 - 10 Dec 2013
a structural reorganization in the material. The XRD spectra also show that the
annealing induces some structural changes in the lm. Three peaks centered around
2θ= 28°, 47° and 55° represent the (111), (220) and (311) Si crystal planes respectively
and the broad peak between 2θ= 20-30° correspond to the small amorphous
nanoclusters [Torchynska 05].
It can be observed from FTIR and XRD analyses that the as-grown and STA
samples are similar. However, in FTIR a higher ordering of the STA sample is seen
from decreasing intensity of LO 4 -TO 4 mode indicating the commencement of phase
separation process. After CA, both FTIR and XRD spectra reect the structural
reorganization of the matrix into SiO 2 and Si. The increased intensity of LO 3 peak
similar to that observed in SiO 2 (ref. Fig. 2.5 of chapter 2) is indicative of Si-np
formation with phase separation process. This is conrmed by the XRD spectra
where we can notice the appearance of Si (111) peak around 28°.
It is interesting to note that the peak around 1107 cm −1 attributed to interstitial
oxygen in SRSO-P15 monolayer is absent in its multilayered conguration.
(b) Atom Probe Tomography
The density and size of the Si-np were estimated by Atom Probe Tomography (APT)
measurements made by Dr. E. Talbot and M. Roussel 3 on CA 50(3/3) ML. Figure
3.18 shows the formation of Si-np and their size distribution in the SRSO sublayer.
This technique provides a three dimensional chemical map of the sample at an atomic
scale. Hence a very accurate and direct characterization of Si-np in SRSO can be
made using APT.
The formation of Si-np in the SRSO sublayer can be seen. The APT studies
revealed the average concentration of Si and O in SRSO sublayers to be 45.7%
and 54.3% respectively indicating about 18.5% Si excess in the material. It can be
noticed that this value of Si excess is lower than the one determined for SRSO-P15
monolayer (37 at.% by RBS). This can be attributed to the thickness of the SRSO
sublayer and/or its growth on SiO 2 sublayers. After CA there is still < 1-2% Si
excess which is attributed to the limit of the experimental set-up. The Si-np density
estimated from this method is 2.6±0.5 x 10 19 np/cm 3 which is higher than our earlier
reported [Maestre 10] Si-np density of 9 x 10 18 np/cm 3 which was also estimated
by APT [Roussel 11]. On the basis of the work of M. Roussel on our layers, the Si
diusion coecient in SiO 2 , D Si is about 5.7 x 10 −18 cm 2 /s after CA. This implies
that a minimum barrier length (l) to prevent diusion in our layers is about 2.03
nm (using l = √ D Si .t A , where t A =annealing time). This value is very close to 1.5
3 Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634, France.
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