Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 13
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QWs, on the other hand, show an increase in emission energy only up down to 100K,
after which there is a sharp decrease in emission energy until the energy levels out at
In addition to the anomalous energy shift, there is evidence of this structure in the
decay lifetime of the IHP QW emission. Figure 2.5b shows the lifetime of the IHP QWs
as compared to that of the c-plane QWs. The most important feature to note here is the
minimum in the lifetime that corresponds with the transition temperature of 100K. Above
this temperature the carriers in the IHP QW are unaffected by the energy level structure
of the QW and are free to move within the IHP. Due to the built-in electric field of the
QW which is oriented along the c-axis of the QW, there is an in-plane electric field
experienced by the carriers, as shown in the skewed energy diagram in Figure 2.3c.
This field acts to separate the carriers, reducing the overlap in the electron and hole
wavefunctions, thus decreasing the recombination rate and increasing the lifetime.
Additional thermal energy acts to weaken the excitonic bonding, resulting in larger
separations and lifetimes.
Below the transition temperature, the step structure begins to affect the carriers.
The carriers relax into the lowest energy section of the IHP QW, which shields them
from recombining non-radiatively at the TD. Lower temperatures result in better
shielding and hence a lower probability of non-radiative recombination. Generally the
non-radiative recombination lifetime is quick compared to the radiative lifetime, so
reducing the probability of non-radiative recombination results in the increase in lifetime
observed for temperatures below 100K.
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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/m1/23/: accessed May 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .