Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 69
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concentration region near the NP, the primary many-body effect that has been
neglected in this model is that of electrostatic screening.
In a semiconductor heterostructure, the excited carriers take the form of a neutral
plasma. Within a semiconductor plasma, the Coulomb interactions are screened off by
free carriers causing the electric field to decay faster than r2. The distance over which
an electrostatic charge is screened by free carriers in a semiconductor is given by the
rD(t) = (5.5.1)
9q2 2 p(t)
Since rD Oc VT/p the strength of attraction due to the image charge effect is
decreased due to screening at higher pumping powers when more e-h pairs are
created. This should result in a power-dependent saturation in the PL intensity.
Experimental evidence of this
1- '"'power-dependent saturation is
presented in Figure 5.7. For
the InGaN QW at 11K at low
power densities (~0.1 mW cm
C2) the Debye radius is about 50
nm, i.e. the screening does not
0 2 4 6 8 10 affect much the forces
Figure 5.5 PL Intensity calculated using Eq. 5.4.5 for attracting the carriers to the
the Au NP (Red) and reference (Black) systems as a
function of time after excitation by an instantaneous sphere. Screening, however,
Gaussian pulse. Note that the decay of the Au NP
system is slower overall than that of the reference. becomes relevant at the
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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/m1/79/: accessed April 27, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .