Hydrosilylation of Silicon Surfaces: Crystalline versus Amorphous

Using thermally induced hydrosilylation, organic molecules were covalently bonded to H-terminated crystalline silicon (111) and hydrogenated amorphous silicon (a-Si:H) surfaces. The resulting chemical surface structure was analyzed by X-ray photoelectron spectroscopy (XPS) and compared to that of silicon surfaces covered by a native oxide or terminated with hydrogen. For both kinds of substrates, the presence of oxygen on the surface is found to hinder the hydrosilylation reaction. Stable H-termination as a starting point for a successful hydrosilylation can be obtained on a-Si:H surfaces with much less technological effort than on crystalline silicon surfaces. Photoconductivity measurements of the different a-Si:H surfaces at low intensity of illumination (monomolecular recombination regime) indicate that the hydrosilylated surface has less defects than the H-terminated surfaces or surfaces covered with native oxide. Spin-dependent photoconductivity measurements identify the dominant paramagnetic defect at the hydrosilylated a-Si:H surface to be the silicon dangling bond.