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

Figure 1.12:
materials.
Energy diagram of bulk Si, Si QDs and their potential insulating barrier
tel-00916300, version 1 - 10 Dec 2013
material to overcome the shortcomings of p-Si. Similar to p-Si, size dependent
luminescence was observed in these congurations also with combined advantages
of mechanical robustness, compatibility with silicon tehnology and chemical stability
for potential applications. The origin of luminescence has opened a debate
and various experimental and theoretical studies attribute it to processes such as
quantum connement eects in silicon nanocrystals [Schuppler 95], silicon oxide: its
defect centers and siloxene derivatives etc.[Deak 92, Duan 95, Cooke 96, Qin 93].
Crystallized Si QDs have high stability against the photo-induced degradation and
stronger light absorption in the lower wavelengths (higher energies). There is also
an increase in the short circuit current due to the absorption of high energy UV
photons within the SRSO lm. This is attributed to the PL re-emitted as red
light that reaches the active p-n junction thereby increasing the photocurrent of
the solar cell [Lopez 11]. The surface passivation of the material often leads to a
reduction in the number of non-radiative centers and allows achievement of ecient
photoluminescence. In contrast to p-Si, it is reported that the spectral band caused
by exciton recombination in Si crystallites does not change practically during aging
[Baran 05]. The electrical properties of SRSO depend on Si concentration and
the QD size [Aceves 96, Aceves 99] and various mechanisms are proposed for carrier
transport such as Fowler-Nordheim, Poole-Frenkel, direct or elastic tunnelling
models [Kameda 98, Salvo 01, Kahler 01].
(b) Si QDs in Si 3 N 4 or Si-Rich silicon nitride (SRSN): The silicon nitride lms
are compatible with silicon technology and have been used as antireection coatings
as well as passivation layers in crystalline silicon solar cells [Aberle 01]. The
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