| The optical properties of Gallium Nitride (GaN) and Zinc Oxide (ZnO) were studied through transmission spectroscopy and photoluminescence. The use of very thin films of less than 0.5 {dollar}mu{dollar}m on a transparent sapphire substrate permitted the direct observation of excitons at room temperature and 77 K in both materials. The films used were thin enough that the absorption coefficient was accurately determined above the band gap. The excitonic structure observed was fit with an excitonic model of absorption determining the exciton binding energy, band gaps and valence band splittings. In the case of gallium nitride the recombination constant was also determined.; In photoluminescence studies of a bulk single crystal ZnO, line narrowing and modal development was observed indicative of stimulated emission and lasing. The photoluminescence of ZnO nanoparticles was also studied and found to be comparable to the luminescence of single crystal ZnO.; Single crystal epitaxial ZnO thin films were deposited by pulsed laser deposition. The as-deposited films were of high quality, but it was found that annealing the films in oxygen could remove the point defects improving the films further. The improvement in the films was quantified through observation of the excitonic structure. It was also found that annealing improved band edge luminescence significantly and reduced defect luminescence.; In photoluminescence studies of polycrystalline ZnO films deposited by sputtering on quartz substrates, it was found that ultraviolet laser light can be used to anneal the ZnO. The unannealed portions of the sample did not emit light while the annealed portions emitted light efficiently. Changes in the film morphology were also observed. |
