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

tel-00916300, version 1 - 10 Dec 2013
Figure 4.13: Raman spectra obtained with dierent laser power densities from 1min-
1000°C and 1h-1100°C annealed SRSN layers. The inset contains the corresponding PL
spectra [laser power density = 1.4 MW/cm 2 , λ excitation =532 nm (2.33 eV)] in the Raman
set-up.
The absence of broad a-Si TA and TO peaks around 150 and 480 cm −1 and sharp
c-Si peak around 510 cm −1 in gure 4.12 conrms the stochiometry of this sample as
indicated by ellipsometry measurements. An overall increase of the Raman curves
is noticed in this gure, which can be related to the shoulder of the PL band. This
argument is supported by the PL spectra obtained at a higher photon ux (laser
power density = 1.4 MW/cm 2 ) in the Raman set-up, that shows emission centered
around 2 eV (Inset of Fig. 4.12). Moreover, a larger shift of the Raman curve is
noticed corresponding to a more intense emission in the CA sample than the STA
layer.
The two peaks around 150 and 480 cm −1 of a-Si is evidently seen in SRSN sample
attesting the presence of excess Si (Fig. 4.13). The absence of sharp c-Si peak
indicates that the material is only composed of amorphous clusters. This conrms
that refractive index alone rules the material properties and not the deposition
approach, since according to our previous arguments with n 1.95eV = 2.32, we are
below the threshold of forming nanocrystals.
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