Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 62
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NP which is non-resonant and yet still produces enhancement. A possible candidate for
this interaction is the electrostatic attraction between the carriers and the image charges
they induce within the metal NPs. I hypothesize that this effect, hereafter referred to as
the "Image Charge Effect", is responsible not only for the enhanced PL and increased
decay lifetime, but also for several other interesting features that I have demonstrated
via experiments to be present in the non-resonant Au NP system.
For emission enhancement to occur one of two things must happen: Either there
is some process which increases light extraction from the semiconductor, i.e. allows
modes that would be trapped within the semiconductor due to total internal reflection to
escape, or there must be some process that increases the internal quantum efficiency
(IQE) of the system. In the Au NP system, the primary mechanism that could be
responsible for increased light extraction from the semiconductor would be the
scattering of light by the Au NPs. Similar to the plasmonic interaction, scattering effects
may be ruled out in the case of Au NPs because the scattering cross-section of the Au
NPs is negligible at the emission wavelength of the QW.
The IQE of semiconductor light emitters depends primarily on the radiative
electron-hole recombination rate, Fradiative. The IQE can be defined as the ratio of
radiative recombination events to total recombination events:
"non-radiatve + "radiative
It is also known that, for semiconductors, both Fradiative and Fnon-radiative depend
upon the concentration n of excited carriers within the QW . In terms of the carrier
concentration Eq. 5.3.1 can be rewritten as :
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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/m1/72/: accessed July 27, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .