Optical Characterization of GaN

• Autor(a) principal: Romero, José António Rodrigues
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/31309
• topic: Gallium Nitride; MBE; HVPE; MOCVD; SHG; Ellipsometry; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

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.