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

2. Reducing the thermal budget of Si-np formation
The second major objective focussed on reducing the thermal budget of Si-np formation.
Strategy: Having established a suitable growth technique, the next investigations
were focussed on the formation kinetics of Si-np in two dierent kind of multilayers
: SRSO/SiO 2 and SRSO/SRSN by subjecting the layers to post fabrication
annealing processes and analyzing the inuence of the annealing time, temperature
and ambience on the Si-np formation.
Outcome: The SRSO/SRSN ML exhibits a high density of Si-np after a short
time annealing (STA) of 1min-1000°C which is almost a magnitude higher than that
obtained from SRSO/SiO 2 MLs after annealing at 1h-1100°C (CA). The results
indicate that the formation kinetics of Si-np in SRSO/SRSN is faster.
tel-00916300, version 1 - 10 Dec 2013
3. Demonstrating the advantages of SRSO/SRSN ML over SRSO/SiO 2
ML
The third major objective concerns the understanding of the two kinds of ML, and
comparing their absorption and emission properties.
Emission properties: It was shown in this thesis that the SRSO/SRSN ML
besides favouring a high density of Si-np, also exhibits intense emission at a low thermal
budget (1min-1000°C) in comparison to SRSO/SiO 2 ML that needs 1h-1100°C.
Besides in SRSO/SRSN ML, an interplay between time and temperature under
nitrogen annealing lead to similar PL intensities (eg. 1h-700°C and 1min-1000°C).
Similarly, an interplay between short-time/N 2 annealing and long-time/Forming Gas
annealing also lead to similar PL intensities while the peak positions obtained by
the two annealing processes are shifted. These results indicate the possibility of
tuning the emission energies by using appropriate annealing treatments. Signicant
emissions were also obtained when SRSO/SRSN MLs are annealed for 0.5h at
temperatures as low as 380°C - 500°C.
Absorption coecients: The absorption coecients obtained from SRSO/SiO 2
MLs even after CA annealing are lower than those obtained from SRSO/SRSN MLs
after such annealing. The absorption coecients of SRSO/SRSN MLs in its asgrown
state or after STA are also signicant (10 4 cm −1 at 3 eV).
Besides the interesting results on optical properties of SRSO/SRSN ML at a
reduced thermal budget, preliminary electrical investigations indicated a two fold
enhancement in conductivity than SRSO/SiO 2 MLs thus demonstrating the advantages
of replacing SiO 2 barrier by SRSN.
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