The presence of the hydrogen complex in Mg-doped GaN poses serious threats for the technological development of blue and ultraviolet light- emitting diodes and lasers. Since hydrogen is a difficult element to work with and it is incorporated into GaN through various mechanisms, a thorough understanding of hydrogen in GaN and other nitrides is essential to meet potential challenges by hydrogen. Most of the work done on the interaction of hydrogen implanted Mg-doped GaN deals mainly with passivation of the dopants and formation of the hydrogen complex with magnesium. However, the role of hydrogen implantation on the optical properties of Mg-doped GaN is not well understood. This study is mainly about optical properties of Mg-doped GaN and the effects of hydrogen on the Mg-doped GaN. Theoretically, group theory is used to determine the total number of symmetry allowed modes in GaN, Raman active modes and possible overtones. Experimentally, Raman and photoluminescence spectroscopy verify the theoretical results. / Dissertation (MSc)--University of Pretoria, 2006. / Physics / unrestricted