The wide-bandgap semiconductor ZnO has gained unprecedented attention due to its potential applications in blue laser diodes and LEDs, optical detectors, high-power amplifiers, and chemical/gas sensing. Progress, however, is still challenged by the high concentration of point defects, problems with stability of the surface, and the lack of reliable p-type doping. The bulk and surface-related defects reduce efficiency of emitters, laser operation lifetimes, and lead to earlier degradation of electronic devices. It is likely that the irreproducible and unstable p-type conductivity of ZnO, which precludes its use as an efficient emitter, is related to self-compensation with unknown defects and peculiarities of the surface conductivity. Compared to the wealth of information now available on exciton emission in ZnO, there is only a small amount of useful and reliable information on surface properties and on point defects responsible for broad luminescence bands. This planning grant supports the development of a collaborative study of defects in ZnO between Virginia Commonwealth University, the Technical University of Braunschweig, Germany, and the Ioffe Physico-Technical Institute, Russia. The investigators and their students develop approaches that involves sample growth, characterization, and modeling, as well as feedback between the activities. US graduate students learn sample growth and preparation techniques and, more generally, experience working at the foreign research laboratories.
