Technical: This project addresses fundamental materials science issues related to p-type doping of ZnO. The approach is to assess the role of compensating defects, and to explore novel schemes for introducing acceptor dopants. Project objectives include: determine the microscopic structure of hydrogen-related complexes in ZnO; investigate and devise novel routes to p-type doping of ZnO; and to evaluate the kinetics and vibrational dynamics of hydrogen in ZnO. Hydrogen donors and acceptor-hydrogen complexes will be studied using vibrational spectroscopy in conjunction with electrical measurements. To probe vibrational dynamics, kinetics, and microscopic structure of impurities, infrared (IR) and Raman spectroscopy will be used to measure local vibrational modes (LVMs) of impurities in ZnO. Hydrostatic pressure will be used as an experimental variable to gain information about the structure of hydrogen-related complexes as well as vibrational interactions between LVMs and lattice phonons.
The project addresses basic research issues in a topical area of materials science with high technological relevance, and is expected to provide unique opportunities for student training. Planned educational activities will benefit a range of students from elementary (K-12) to graduate students. Related efforts include community outreach programs to local schools and home schooled children, the development of lecture demonstrations for solid-state physics courses, and undergraduate research opportunities. In conjunction with research, these activities are expected to encourage students from diverse backgrounds to enter fields related to materials science and solid-state physics. Graduate and undergraduate students will have an opportunity to perform forefront research and, upon graduation, make significant contributions to science and engineering.
Zinc oxide, the stuff used in sunscreen, has emerged as an important material for light-emitting technologies. It turns out that zinc oxide crystals emit UV light with extremely high efficiency and little wasted heat. This property could be harnessed to fabricate future generations of energy-efficient white lights. Despite its potential advantages, the lack of control over defects and impurities has hindered the development of this material for use in devices. In this NSF project, researchers investigated the atomic-scale properties of defects in zinc oxide. By growing crystals in an ammonia atmosphere, nitrogen impurities were deliberately introduced into the material. Nitrogen is an "acceptor" dopant, meaning that it accepts electrons from the crystal. Such dopants are required for practical devices. The researchers determined that, as grown, nitrogen forms a bond with hydrogen. This bond can be broken by heating the crystal, resulting in isolated nitrogen acceptors. This process, or a similar one, may provide a means for fabricating devices that emit light efficiently. Four undergraduate students and four graduate students were involved in this research. During the report submission period (summer 2010), the PI and two students traveled to the Advanced Light Source (ALS) at the Lawrence Berkeley National Lab in Berkeley, California. The experiments at the ALS used x-rays to probe the structure of zinc oxide as it is subjected to high pressures. These experiments are important to determine how zinc oxide layers will behave in devices, where they will be under significant mechanical strains. Two undergraduate students also performed high-pressure experiments, at WSU, as part of a Research Experiences for Undergraduates (REU) program.
