Conductivity changes in zinc oxide and magnesium zinc oxide nanoparticle films annealed in hydrogen ambient

This dissertation explores the physics of how the electrical properties of ZnO and MgZnO nanoparticle films are modified when exposed to hydrogen gas at high temperatures. Specifically, with the goal of quantifying the ease of incorporation of the hydrogen atom and its properties as a donor. The nanoparticles were grown on insulating silicon substrates and had an average diameter of 40 nm. The devices were of a two terminal design, where the terminals consisted of two 25 mum diameter gold wires laid parallel to each other on the nanoparticle film to measure the current passing through the film. For the first set of experiments when nanoparticles were exposed to H 2 gas at room temperature, no significant changes in the current-voltage behavior of the nanoparticles were observed relative to measurements done in vacuum. Annealing in H2 below 370K resulted in no significant change in the current. Both the ZnO and MgZnO nanoparticle films showed significant changes at about the same threshold temperatures when annealed to 400K. A second set of experiments were carried out in temperatures up to 500K following the same procedure that showed similar but more complex behavior. The formation energy of hydrogen incorporation was calculated by analysis of the solubility of hydrogen in ZnO at various temperatures. Donor energy level of the nanoparticle films was also calculated by analyzing the post-doping conductivity in vacuum as a function of temperature. The origin of the change in I-V characteristics of ZnO and MgZnO nanoparticles when annealed in H2 ambient, the reasons for the differences of hydrogen doping results between nanoscale and bulk, and the mechanism of hydrogen behavior in the nanoparticle films will be discussed in detail.