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

properties. The increasing Si incorporation with refractive indices is reected in all
the characterization techniques. Based on the investigations, the results on SRSN
can be summarized under two categories:
(a) n 1.95eV ≤ 2.4
ˆ There is no formation of nanocrystals. For samples with low refractive indices
(n 1.95eV =2.0-2.2) the absence of nanocrystals is attributed to the low Si excess
and to the low D Si in SRSN as compared to SiO 2 . For samples with refractive
indices between 2.3-2.4, this may be attributed to the low power density
provided during thermal annealing, which does not favour crystallization.
tel-00916300, version 1 - 10 Dec 2013
ˆ The material exhibits photoluminescence depending on the applied laser power
density.
ˆ With increasing refractive indices (Si excess), the emission decreases and the
absorption coecient increases.
(b) n 1.95eV ≥ 2.4
ˆ The threshold of refractive index for forming nanocrystals in SRSN matrix
is demonstrated. XRD and Raman measurements conrm the presence of
nanocrystals.
ˆ No emission is observed from PL measurements whatever be the annealing,
while from Raman measurements emission is witnessed. This emission
is quenched after 1h-1100°C annealing. Correlation between formation of
nanocrystals and quenching of PL suggest that nanocrystals might have a
detrimental eect on emission in SRSN materials.
ˆ The absorption coecient decreases with increasing sample thickness.
4.5 SRSO/SRSN multilayer
The microstructural and optical analyses of SRSO/SRSN MLs grown by RF sputtering
technique is demonstrated in the following sections. It was seen in chapter
3 that the best material properties in SRSO/SiO 2 MLs (formation of nanocrystals,
emission, absorption etc.) are obtained after CA (1h-1100°C annealing). Hence
the SRSO/SRSN ML is also subjected to CA for initial investigations. The material
properties of CA sample are compared with those obtained from their as-grown MLs.
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