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

tel-00916300, version 1 - 10 Dec 2013
in the ML and TEM images also reveal a perfect alternation of the SRSO and SRSN
sublayers. The pattern thicknesses estimated from XRR and TEM are in agreement
with each other thereby demonstrating XRR is a sucient technique to estimate the
pattern thickness of a ML. High density of Si-np even after STA (1min-1000 °C/N 2
annealing) is witnessed from HRTEM and EFTEM images. The Si-np are formed
only in the SRSO sublayers.
FTIR: The combined contribution of the longitudinal and transverse optical
modes from SRSO and SRSN sublayers is seen in the FTIR spectra. The blueshift
of the Si-N peak indicates an increase in Si-np and nitrogen content with annealing.
Similar blueshift and changes in peak intensity associated with the formation of
Si-np is observed in the Si-O related bonds.
XRD: The investigations on as-grown, STA (1min-1000°C) and CA (1h-1100°C)
SRSO/SRSN MLs reveal the presence of Si-np in as-grown state crystallize upon
annealing.
Absorption coecient : The CA sample has absorption coecient higher
than that of as-grown or STA sample over the whole energy range. However, at 3eV
the STA sample also possess high α ∼ 10 4 cm −1 comparable to the CA sample.
PL: An extensive investigation on the emission behaviour of the ML was made
resulting in following observations and understandings:
ˆ An interplay between time and temperature of annealing : low time/high
temperature (1min-1000°C) & long time/low temperature (16min-700°C) lead
to similar PL intensities. Among these STA (1min-1000°C) is identied to be
better owing to a lower thermal budget than 16min-700°C.
ˆ The highest PL is obtained after STA (1min-1000°C) and almost totally quenched
after CA (1h-1100°C).
ˆ The highest PL is attributed to the presence of a high density of amorphous
clusters, and the quenching is related to the detrimental eect of SRSN sublayers
on emission properties with annealing.
ˆ Most of the PL spectra can be decomposed into three emission peaks whose
origin were investigated. The central peak between 1.5-1.75 eV is attributed
to the Si-np 1.9 eV to the defects in SRSN sublayers. The peak at the lower
energies is still under investigation and the possible contribution of optical and
geometrical eects on this peak is suspected.
ˆ The pattern thickness, SRSN sublayer thickness as well as the time spent in
the deposition chamber are found to be important factors that control the
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