Role of the Surface in the Electrical and Optical Properties of GaN and ZnO

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Technical. This project addresses the role played by surfaces and interfaces in the electrical and optical properties of GaN and ZnO. It thought that surface-related effects may be responsible for reduced efficiency of emitters, shorter laser operation lifetimes, and earlier degradation of elec-tronic devices. Additionally, the irreproducible and unstable p-type conductivity of ZnO may be related to peculiarities of the surface conductivity in this material. This project aims for an in-depth investigation to gain a comprehensive understanding of the processes at and near the sur-face for both GaN and ZnO. Electrical and optical properties will be probed under different am-bient conditions, temperatures, and illumination. Band bending near the surface and its variation under illumination (photovoltage) will be studied using two methods: 1) a Kelvin probe com-bined with an optical cryostat; and 2) a microscopy technique combining local charge injection with subsequent imaging of the surface charge. The underlying mechanisms for surface band bending will be related to sample preparation, temperature, and ambient environment. Effective passivation schemes will also be explored to improve the performance of optical and electronic devices based on these wide-bandgap semiconductors.Non-Technical. The project addresses fundamental research issues in a topical area of elec-tronic/photonic materials science having technological relevance. This effort may lead to higher reliability, longer lifetime, and higher efficiency bright light sources based on GaN and ZnO. The proposed research program will leverage strong collaborations between research groups in the Departments of Physics and Electrical Engineering at Virginia Commonwealth University (VCU), as well as initiate a collaboration with the Department of Chemistry and Physics at Longwood University, a nearby undergraduate institution. The project provides support for graduate students at VCU and undergraduate students at both VCU and Longwood, where all of the students will be involved in collaborative efforts between multiple research groups. Women and underrepresented minority groups will be actively recruited and supported within this pro-ject. VCU is a growing urban university with a diverse student body (18% African American, 22% other minorities), and the PI?s have a record of mentoring students from underrepresented groups in their laboratories. An international collaboration is also planned with the Ioffe Physical Technical Institute of the Russian Academy of Science.