Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 21
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will cover near-field measurements using a near-field scanning optical micro-
3.4 Far-field PL
The most common method of characterizing a light-emitting sample is through
far-field PL measurements. In this experiment the sample is excited-in this case an
InGaN/GaN MQW-and the wavelengths of the emitted photons are measured.
Generally this measurement is achieved using either a monochromator (which uses a
diffraction grating to single out a very narrow range of wavelengths) along with a
photodiode to measure the intensity at that wavelength, or a diffraction grating
combined with a CCD (charge-couple device) detector. The latter has the benefit of
being able to simultaneously capture the intensities over a wide range of wavelengths,
speeding up the process significantly.
Figure 3.2 depicts the experimental setup used for PL measurements in this
work. Excitation is achieved using the 325 nm line of a HeCd continuous-wave (CW)
laser. The 442 nm line of the HeCd is separated out using a prism and beam stop, and
the remaining line is directed to the sample using UV-Vis mirrors. The emission from the
excited sample is then directed through a pair of collimating lenses to focus the emitted
light on the entry-slit of a Triax 550 spectrometer, which contains the aforementioned
diffraction grating and CCD.
The result of the measurement is a spectrum which displays the emitted intensity
versus wavelength (or energy) of the photons. It is important to note that this measured
intensity depends directly upon many factors, e.g. the alignment of the laser and
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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/m1/31/: accessed July 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .