Grain boundary studies in zinc oxide thin films

ZnO holds a unique position among materials because it is piezoelectric, transparent in the visible and can be made conducting with appropriate doping. Its piezoelectric property has been exploited considerably in thin film applications like SAW devices. Concurrently, doped ZnO along with indium tin oxide is the material of choice for transparent conducting electrodes in solar cells and flat panel displays. Moreover, in the recent years, with the emergence Al{dollar}sb{lcub}x{rcub}{dollar}Ga{dollar}sb{lcub}1{lcub}-{rcub}x{rcub}{dollar}N based blue LED's, there is also a resurgence in the interest for epitaxial single crystal ZnO films. All of the above and its potential use as thin film sensors make it a technologically important material to study.; Previous studies indicate that grain boundaries exist in both textured and epitaxial ZnO films. While textured films are expected to contain a range of grain boundaries (from low to high angle grain boundaries), epitaxial films contain only low angle grain boundaries. In the present work, we are interested in the role these grain boundaries play in determining the electrical and optical characteristics of ZnO films.; In the following dissertation, the defect equilibria, the nature of the grain boundary potential and the grain size achieved in ZnO films grown on sapphire and glass and how they define the global electrical and optical properties of the film is presented. Finally, a novel technique of manipulating grain boundary potentials and its potential use in fabricating thin film varistors with high switching voltages is discussed.