Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 15
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the strains in the x, y and z directions (z being parallel to the c-axis). Assuming biaxial
strain and pseudomorphic growth, we can assume that Eyy = Eand that Egg =
-2(c13/c33) Egy, where c13 and c33 are stiffness constants. This gives us:
Pz = 2 [e31 -(c13/c33) ]Exx (2.4.2)
This can be converted into an electric field simply by dividing by ErE0.
The presence of this electric field within the QW leads to a separation of the
carriers to opposite ends of the QW, leading to a reduction in overlap of the electron
and hole wavefunctions. This reduced overlap causes an increase in the radiative
recombination lifetime of the QW. Furthermore, the skewing of the band structure due to
the electric field effectively reduces the energy separation between the electron and
hole states, resulting in a red-shifted emission. Figure 2.6 shows a typical band-
structure of an InGaN/GaN QW structure. This red-shift due to the built-in electric field is
known commonly as the quantum-confined Stark effect (QCSE) .
The strength of the QCSE turns out to be excitation-power-dependent. As
carriers are excited, they separate out to opposite sides of the QW and thereby screen
some of the electric field. At high excitation-power densities, the number of carriers
becomes large enough to effectively screen the internal electric field, resulting in a blue-
shift in emission and a decrease in the recombination lifetime . Furthermore QCSE
has been shown to produce non-exponential decay in InGaN QWs due to the
dependence of the lifetime on the carrier concentration, and hence on time. 
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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/m1/25/: accessed November 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .