NSF-CGP Fellowship: Correlation of Stress with Hydrogen Microstructure and Photodegradation in Hydrogenated Amorphous Silicon

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9802430HanThis award provides funds to support a 3-month research visit by Dr. Daxing Han, Department of Physics and Astronomy, University of North Carolina at Chapel Hill, for collaboration with Dr. Shoji Nitta, Department of Electrical Engineering, Gifu University, Japan. These two collaborators will investigate the photo-induced changes on stress and its correlation with hydrogen microstructure as well as the density of electronic defect states in hydrogenated amorphous silicon (a-Si:H). This material, a-Si:H, is a leading candidate for thin film transistor arrays to drive large-area flat panel displays and for the development of clean energy from solar cells, as well as for large-area photo-sensor arrays. It has been found that the conventional, non-hydrogen diluted glow discharge intrinsic material has very high stress. This material shows photo-degradation, but its stabilized properties are still quite good for large area devices such as solar cells. It has been unclear, however, whether the stress is correlated with the light-induced metastability, or whether there is a correlation of stress with hydrogen microstructures in a-Si:H. Recent results indicate that significant improvement in stability of a-Si:H solar cells has been made by hydrogen dilution during the conventional glow discharge and by the hot filament assisted chemical vapor deposition technique.The research group at Gifu University recently developed an innovative tool, the atomic-force-microscope, utilizing a bending-beam method, that is sensitive to weak stress such as the light-induced changes of the stress in a-Si:H deposited on thin quartz. These more stable "new" amorphous-silicon materials and the innovative tool offer a unique opportunity to elucidate the correlation between the stress and hydrogen microstructure as well as the electronic properties in a-Si:H. The proposed investigations will help provide an insight into the microstructure origin of the metastability and enhance the evidence for the correlation between structural and electronic states in this amorphous silicon network. This project is supported under the Science Fellowship Program between the National Science Foundation and the Japan Foundation Center for Global Partnership.***