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Optical Characterization of GaN
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Gallium nitride is a direct bandgap semiconductor commonly used in LED’s and lasers.
Its wide bandgap, high thermal conductivity and ability to operate at high frequencies
and power make it an attractive material in the semiconductor industry.
In this thesis two different samples of gallium nitride were characterized through
four different linear and non-linear optical characterization techniques: a) optical secondharmonic
generation, b) photoluminescence c) Raman spectroscopy and d) ellipsometry.
Concepts in optics for anisotropic media and non-linear crystals required for the characterization
techniques are discussed, and three of the most commonly used epitaxial
growth techniques used for GaN growth for either thin films or bulk are described.
Moreover, to complement, and validate and to get a better understanding of the experimental
results obtained computational simulations for ellipsometry and second harmonic
generation were also implemented in the Python programming language.
Raman and photoluminesence spectra were compared with other published work,
allowing us to compare the crystalinity and purity of the samples. Both mathematical
models for ellipsometry and second harmonic generation were fitted to the experimental
results, allowing us to conclude that it is possible to determine the thickness of a thick
crystal through second harmonic generation, where ellipsometry no longer is a reliable
method.
Descrição
Palavras-chave
Gallium Nitride MBE HVPE MOCVD SHG Ellipsometry