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

tel-00916300, version 1 - 10 Dec 2013
noticed that the intensity obtained after 4.75h-FG + STA is higher than that of
100(3.5/5) STA ML (Fig. 4.42). This suggests that the time spent under 500 °C in
4.75h-FG process in 50(3.5/5) has a similar eect of the 4.75h excess time spent by
100(3.5/5) in the deposition chamber.
Figure 4.42: Investigating the PL spectra
obtained from 50(3.5/5) SRSO/SRSN ML after
FG+STA. (The PL spectra obtained after
STA (1min-1000°C N 2 ) from 50 and 100 patterned
MLs are also given in dotted lines for
comparison).
One possible reason could be the exodiusion
of hydrogen at such high temperature
(500°C) resulting in Si dangling
bonds that reorganize to act as nucleating
sites in the SRSO sublayers. Hence,
a STA (1min-1000°C in N 2 ) treatment
that follows after this time and temperature
of exposure is sucient to result in
a high density of Si-np. Thus, we may
say that the emission intensity increases
with increasing density of nanoclusters
resulting in emission enhancement of 50
patterned sample.
These results indicate that the time
spent at high temperature (500°C-either
in deposition chamber or in post fabrication
process) prior to STA has a huge
inuence in favouring emission. The dierent peak positions of 100(3.5/5) STA ML
and 50(3.5/5) 4.75h+STA ML, can be attributed to the dierent annealing processes
employed on these two MLs. Thus, these studies demonstrate the possibility of enhancing
the emission of a SRSO/SRSN ML by reducing the material (50 patterns
vs. 100 patterns) subjecting to a pre-thermal treatment before STA.
4.10 Understanding the origin of photoluminescence
A detailed investigation on various annealing treatment on the PL spectra in the
previous sections suggested various possible origins for emission. It was seen in
section 4.6 that mostly all the PL spectra obtained from samples annealed under
N 2 atmosphere had three peaks. From the peak positions in all the investigations
above, we might attribute a range of positions for these peaks named as (1,2,3) in
100(3.5/5) ML and (a,b,c) in 50(3.5/5) ML. They are,
- Peak (1) (a) and (b) :1.2-1.45 eV
- Peak (2) and(c): 1.50-1.7 eV
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