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

3.8.4 Inuence of SiO 2 barrier thickness
tel-00916300, version 1 - 10 Dec 2013
In order to understand better the role of t SiO2 , the SiO 2 sublayer thickness was varied
between 1.5 nm to 10 nm, while the SRSO sublayer thickness and total number of
patterns were xed to be 3 nm and 50 respectively. Figure 3.23 shows the as-recorded
PL spectra from these layers.
It can be seen that the PL intensity
obtained with t SiO2 =1.5 nm is very
low, which can be attributed to the
overgrowth of particles due to a low
barrier height. The emission intensity
increases with barrier thickness which
might be attributed to a better con-
nement within SRSO sublayer and/or
to some optical and geometrical eects.
But, the higher barriers that lead to
better emission properties would on the
contrary lower the conductivity. Hence
considering a balance between optical
and electrical properties needed for a
PV device, t SiO2 ranging between 3-3.5
nm can be an optimized barrier thickness.
Figure 3.23: PL spectra of 50 patterned ML
with t SRSO = 3nm and t SiO2 varying between
1.5 nm to 10 nm to investigate the inuence
of SiO 2 barrier thickness.
3.9 Summary on SRSO/SiO 2 multilayers
ˆ FTIR and XRD analyses indicate the formation of amorphous Si-np even in
the as-grown state, a part of which crystallizes upon annealing.
ˆ The peak attributed to interstitial oxygen (about 1107 cm −1 ) in FTIR analysis
of SRSO monolayers disappears in SRSO/SiO 2 multilayers.
ˆ A high density of Si-np with a size control is achieved (about 3 x 10 19 np/cm 3 )
in SRSO sublayer.
ˆ APT analysis reveal that the diusion of Si occurs in SiO 2 sublayers with thicknesses
lower than or equal to 3 nm.
ˆ The SRSO-P15 when used in a ML conguration results in intense visible emission
in comparison to the absence of emission in its monolayer conguration.
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