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

4.10.2 Eect of Si-np Size distribution
tel-00916300, version 1 - 10 Dec 2013
The origin of peak (2) has been attributed to Si-np following the quantum connement
eect throughout our earlier discussions. In order to conrm this, investigations
were done relating the experimentally obtained Si-np size with the Delerue law
[Delerue 93]. The size of Si-np in a 3.5 nm SRSO sublayer has been estimated to be
3-4 nm from experiments in chapters 3 and 4, leading to a peak position of about
1.6 eV with the Delerue law. This peak position can be related to peak (2).
The peaks (1, a & b) between 1.2-1.45eV is seen mostly only in N 2 annealed
samples. This peak is seen to redshift with increasing t A , similar to peak (2). Since
increasing t A may lead to increasing Si-np size, we may suppose that these peaks
also follow a quantum connement model. Using the Delerue's law to identify the
peaks between 1.2-1.45 eV range results in particle sizes ranging between 5.5-13.5
nm. Though, we may suppose the possible formation of 5.5 nm Si-np due to some
overgrowth at the interfaces, but 13.5 nm for the lowest energy is impossible since
we do not observe a breakdown of multilayer structure to result in such big Si-np.
The TEM image of 100(3.5/5) ML which has peak (1) at low emission energy (1.24
eV) conrms that we have perfect alternations of the two sublayers, and EFTEM
also conrms the presence of Si-np restricted to SRSO sublayer. Therefore, this
peak cannot be attributed to such big Si-np even at SRSO interfaces. From our
XRD, TEM and EFTEM observations, we have conrmed the absence of Si-np in
SRSN either in crystalline or amorphous form. Thus, it can be said that this peak
is not necessarily related to Si-np in SRSO or SRSN sublayers but has some other
origin such as interference which will be analyzed in the next chapter.
4.10.3 Eect of surface microstructure
The surface microstructure of STA and FG annealed samples has been investigated
by optical microscopy performed on 50(3.5/5) SRSO/SRSN ML (Fig. 4.45). It
can be noticed that, with N 2 annealing the sample surfaces show the appearance of
circular spots as already shown in gure 4.21 on 100(3.5/5) CA sample.
The surfaces of both STA and CA annealed samples are similar and show the appearance
of circular spots after annealing. Moreover, there is no signicant change in
the size of these spots with annealing. The surface microstructure of STA 50(3.5/5)
ML is similar to 100(3.5/5) ML, but the size of the circular spots increase for CA
100(3.5/5). The inuence of STA and CA on the PL intensity are the same on
the 50 and 100 patterned MLs, despite the pronounced surface dierence after CA.
Concerning the FG annealed samples, there is no dierence on the surface structure
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