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

A multilayer composed of 100 patterns of 3.5 nm-SRSO and 5 nm-SRSN, (which
will be referred as 100(3.5/5)) is chosen as a typical example for these initial investigations.
The SRSN sublayers in this sample are grown using reactive sputtering
approach.
4.5.1 Ellipsometry
The total thickness, roughness and pattern thickness of the 100(3.5/5) ML were
analyzed using ellipsometry. Figures 4.16 and 4.17 show the results of ellipsometry
simulations of the as grown and CA samples. The ts were performed assuming the
SRSO/SRSN multilayer to be a constant refractive index homogenous layer.
tel-00916300, version 1 - 10 Dec 2013
(a)
Figure 4.16: As-grown 100(3.5/5) ML. (a)Fitting of the ellipsometric functions (Is & Ic
as a function of photon energy). The circles relate to experimental spectra and the lines
to the tting, and (b) The dispersion curves, n eV & k eV of the real and imaginary parts
of refractive indices respectively; n 1.95 eV = 2.137 is highlighted in the gure.
(b)
It can be noticed in the results obtained from as-grown and CA 100(3.5/5) MLs
(Fig. 4.16a and 4.17a) that with such an approximation the theoretical spectra
well t the measured ones. Moreover, the 832 nm thickness of the as grown sample
deduced from ellipsometry closely relates to the expected thickness of 850 nm
[(100 pattern x 3.5 tSRSO ) + (100 pattern x 5 tSRSN )]. As highlighted in gures 4.16b and
4.17b, the refractive index of the as-grown sample, n 1.95eV =2.13 increases to 2.34
after CA. This increase is also accompanied by a reduction in thickness of the CA
sample to 777 nm (as-grown sample = 832 nm) thereby indicating a densication
process favoured by annealing.
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