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

In case of multiple emission bands in the material (n kind of emitters), the
cross-sections are considered as a superposition of contribution of all the bands, as
expressed by equation 5.36. In this thesis, the choice of a single absorption band is
made.
σ em. = ∑ n
i=1 σ em.max
1 +
1
(ω 2 ij(em.) −ω2 ) 2
ω 2 ∆ω 2 (em.)
Eqn (5.36)
When the dynamic gain exceeds the dynamic losses, emission peak is evidenced
in medium 1. Figure 5.14 shows the dependence of emission intensity on the thin
lm absorption (dynamic losses) and dynamic gain.
tel-00916300, version 1 - 10 Dec 2013
(a) σ emis.max = 10 −20 m 2 (b) σ emis.max = 10 −17 m 2
Figure 5.14: Dependence of emission intensity with dynamic gain and maximum emission
cross-section obtained by simulations.
The graph is represented in energy scale to facilitate comparison with previous
chapters. The simulation is done on a SRSO monolayer with arbitrary parameters
for illustration: 1.5 refractive index, 500 nm thickness, 770 nm emission centre (1.61
eV) and σ abs.max = 10 −20 m 2 . Figure 5.14(a) shows that when σ emis.max = 10 −20 m 2
= σ abs.max (arbitrarily xed values), the loss is higher than the gain, and no emission
is witnessed at 1.61eV. While increasing the emission cross-section to 10 −17 m 2 , the
PL peak emission is evidenced as shown in gure 5.14(b), due to the positive net
gain. This shows that the balance between absorption and gain plays a dominant
role in the emission intensity.
The PL peak position maximum is located at 1.6 eV which diers from the
position of the maximal gain. This dierence in the maximum position of the peaks is
attributed to the optical cavity eect of the thin lm. In both the cases investigated,
there are few alternating shoulders situated at similar positions which are indicative
of interference mechanisms in the lm.
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