Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 22
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sample, alignment of the collimating lenses, slit-width, time of integration of the CCD,
etc. Because of this, great care must be taken when directly comparing measured
intensities between samples. Furthermore, it is for this reason that the units of
measured intensity in PL measurements are generally labeled a.u. or arb, short for
Even in the absence of direct comparisons of intensities between spectra there is
still a significant amount of information that can be extracted from spectra. For instance,
if we normalize the spectra such that the total area under the curve is unity, then the
intensity represents the probability of emission at that wavelength. In many cases the
distribution of probabilities is or is close to Gaussian, and so we can estimate not only
the peak energy of emission but also other parameters such as the full-width at half-
maximum (FWHM) which is related to the standard deviation of the energy of the
photons, and identify other emission peaks as well. I will discuss how to extract this
information in detail at the end of this chapter.
While a spectrum taken at room temperature gives us a good deal of information
about the sample, we can gain more information if we tweak one variable while holding
the others constant. The next three sections involve variations of PL using this method.
3.4.1 Temperature Dependent PL
Temperature in a semiconductor affects many properties of the sample. For
example the concentration of phonons within the medium decreases with decreasing
temperature, as does the mobility and average velocity of excited carriers within the
system. Additionally, the probability of non-radiative recombination with defect sites
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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/m1/32/: accessed March 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .