Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 63
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7 = (5.3.2)
A n + B n2 + Cn3
Here B is proportional to the probability of radiative electron-hole recombination,
and A is proportional to the defect density within the QW, and C to the probability of
Auger recombination involving three carriers. It should be clear from Eq. 5.3.2 that,
since the non-radiative term is linear in n and the radiative is quadratic in n, increasing
the carrier concentration will increase the IQE of the system. I will demonstrate
throughout the following two chapters that the image charge effect produces an
increase in the IQE by producing strongly increased carrier concentrations in the vicinity
of the NPs. For purposes of our modeling, I neglect the Auger recombination term as
the term C is of the order 10-30 in InGaN , which means Auger recombination plays
no significant role at carrier concentrations of 1018 cm-3 and below.
In the case of plasmonics, IQE is increased by the addition of a second radiative
recombination path provided by coupling to the SPs. This contribution of this new path
becomes significant when the energy of emission of the QW matches the resonant
energy of the SPs present. This enhancement occurs due to an increase in the rate of
spontaneous e-h recombination [6, 7, 57] due to the Purcell effect .
The carriers in the QW, however, interact with the metal NPs not only through the
evanescent SP fields but also via long-range Coulomb forces. When carriers are excited
in the QW by an incident photon, the excited carriers are no longer electrically neutral.
When excited near a metallic NP, the electric field produced by the carriers must induce
a polarization in the NP which can be modeled for simple geometries as a charge
distribution of equal and opposite magnitude within the metal. Since the induced charge
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Llopis, Antonio. Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures, dissertation, May 2012; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc115113/m1/73/: accessed April 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .