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

(a) 1min annealing vs. T A . (b) 1h annealing (LTA) vs. T A .
Figure 4.32: Eect of time and temperature of annealing on the emission of 100(3.5/5)
ML.
tel-00916300, version 1 - 10 Dec 2013
It can be clearly seen that the increase in emission intensity accompanied by
a redshift occurs only till 1000°C. With further increase in temperature (1050°C),
the PL is quenched and a blueshift is observed. The emission continues to decrease
for the highest temperature employed, but the PL peak position is redshifted which
could be due to the merging of peak (1 & 2). The intensity of peak (3) decreases
with temperature and and completely disappears for the two highest temperatures.
The increase in emission intensity with a redshift till 1000°C can be attributed to an
increase in the density and size of the Si-np. Figure 4.32b shows the eect of LTA
on the PL emission and it can be seen that the PL shape and intensities obtained
by step annealing for 61min and continuous annealing (i.e. LTA) are the same. The
PL quenches with high temperatures despite the formation of nanocrystals.
4.6.6 Structural analysis on STA SRSO/SRSN ML
In order to understand the reason behind the emission behaviour, structural investigations
were performed on STA (1min-1000°C) 100(3.5/5) ML. Figure 4.33 shows
the XRD spectrum of the sample. The peak between 20-30° is neither broad as in
the as-grown sample, nor sharp as in the case of CA sample as observed in gure
4.22. This implies that the sample is a mixture of both amorphous and crystalline
Si-np. Since after CA, there were no nanocrystals in SRSN sublayer as observed by
TEM, the formation of crystalline Si-np as suggested by XRD should be only within
the SRSO sublayer after STA.
But it was seen from SRSO/SiO 2 MLs that a minimum annealing treatment of
1h-900°C is needed to form Si-nanocrystals in SRSO sublayers. Therefore, in order
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