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

tel-00916300, version 1 - 10 Dec 2013
on these PL spectra indicate that there is only one low energy peak when the t SRSN
is the lowest (=1.5 nm), and the presence of three peaks is observed for all other
t SRSN .
The peaks are blueshifted with increasing
t SRSN and the positions of peak
(b & c) reach the highest value for the
two highest t SRSN . Similar trend of PL
intensities and peak shifts with varying
Figure 4.38: Inuence of t SRSN on the
PL spectra of SRSO/SRSN ML grown by
reactive sputtering approach, after CA (1h-
1100°C).
t SRSN is observed in MLs with SRSN
grown by co-sputtering approach (not
shown here). This blueshift may indicate
a better connement provided by
SRSN barriers with increasing t SRSN
thereby preventing overgrowth of Si-np
at the interface of SRSO and SRSN sublayers.
The absence of peak (c) for the
lowest t SRSN and the gradually increasing
appearance for higher t SRSN con-
rms the attribution of this peak to
SRSN sublayers. The samples were also subjected to CA to observe the inuence
of t SRSN emission properties after such annealing (Fig. 4.38). The PL after CA
is largely quenched, but t SRSN plays a role in the emission intensity of CA MLs
as well. The increase of PL intensity around 1.5 eV with increasing t SRSN is seen
accompanied by a blueshift of the peak position. Similar to our arguments on STA
emission behaviour, this increase in peak intensity can be attributed to the SRSN
barrier leading to a greater connement of the Si-np formed within SRSO, with increasing
t SRSN . Consequently, the size of the Si-np decreases resulting in a blueshift
and an enhanced emission.
4.9 Optimizing annealing treatments
It has been demonstrated in section 4.6 on nitrogen annealing that the SRSO/SRSN
MLs are advantageous over SRSO/SiO 2 MLs by achieving higher emission properties
at a lower thermal budget either by using short time annealing at high temperature
(eg. 1min-1000°C [STA]) or longer time at low temperatures (eg. 16min-700°C).
Besides, a high density of Si-np is formed after STA resulting in higher absorption
behaviour than SRSO/SiO 2 MLs. It has been reported that the passivation of silicon
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