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

(a) Typical FTIR spectra.
(b) ν LO3 and ν T O3 vs. annealing.
Figure 3.20: (a) Typical FTIR spectra from 70(4/3) ML showing the eect of annealing
and (b) LO 3 and TO 3 peak position variations with annealing.
tel-00916300, version 1 - 10 Dec 2013
the gure for comparison. The increasing intensities of LO 3 and TO 3 modes with
annealing indicate the evolution of phase separation process.
Figure 3.20b shows the variation of LO 3 and TO 3 peak positions with annealing
in all the MLs under investigation. Irrespective of the sublayer thicknesses, the LO 3
and TO 3 peak positions reach the same point after CA. This could be attributed to
an almost complete phase separation process after such annealing treatment, in the
view of the sensitivity of the experiment.
3.8.2 Atom probe tomography
The inuence of the sublayer thickness (t SRSO /t SiO2 ) as well as CA treatment on the
formation of Si-np were investigated by APT on three samples with t SRSO /t SiO2 = 8
nm/10 nm , 4 nm/3 nm and 4 nm/1.5 nm respectively (Fig. 3.21). The as-grown
samples were also analysed for comparison.
Special attention is laid on MLs with t SiO2 = 1.5 nm and 3 nm in this study, to
understand the diusion and interlayer grain growth shown in section 3.8.2.
The presence of small clusters of Si is seen in the as-grown sample in support to all
our previous discussions about high T d and Si excess favouring such a formation. It
can be also seen that the Si-np size is controlled along the growth direction after CA
treatment. As expected, the size of Si-np is large in 8 nm thick SRSO sublayer but
the 4 nm SRSO sublayer also shows big Si-np if separated by 1.5 nm SiO 2 sublayer.
This is in agreement with the explanation above on diusion length (about 2 nm)
of Si in SiO 2 which results in the overgrowth of Si-np to form larger crystals. The
Si-np are smaller with 3nm thick SiO 2 sublayer, but still there are few big crystals
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