Theoretical studies of aromatic silicon-based structures and their application to photostructural changes in hydrogenated amorphous silicon

Abstract

The self-consistent-field X-alpha scattered-wave technique has been used to investigate the electronic structure of aromatic silicon-based clusters which can be expected to form some of the defect centers in hydrogenated amorphous silicon (a-Si:H) thin films. These clusters, which are planar rings containing 4n+2 π-electrons, exhibit resonance stabilization and give rise to the silicon analogue of aromatic hydrocarbons. We have studied Si 6(sat) 6 and Si 4O(sat) 4 clusters in comparison to benzene (C 6H 6). The silicon-based clusters are less stable than benzene due to larger interatomic separations as well as shielding effects of the Si 3s electrons. However, our results show that Si 4O(sat) 4 is more stable than Si 6(sat) 6. The introduction of oxygen into such resonant rings adds stability by increasing the strength of π-bonding throughout the ring. As a result, we show how the presence of such structures in a-Si:H can account for the photostructural effects observed in thin films of these materials.