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A10.5.1

Hydrosilylation of Silicon Surfaces: Crystalline versus Amorphous Andrea Lehner, Georg Steinhoff, Martin S. Brandt, Martin Eickhoff, Martin Stutzmann Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany ABSTRACT 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.

INTRODUCTION Stable, densely packed organic monolayers covalently bonded directly to silicon surfaces currently are of significant interest in the field of biosensor applications, e.g. in biochemistry and biophysics, as they in principle allow the detection and utilization of charge transport across the silicon/organic interface. Preparation of such surfaces can be performed by hydrosilylation of Hterminated silicon with alkenes or alkynes [1]. For hydrosilylated crystalline silicon (111) surfaces, a high chemical and thermal stability [2] as well as good electronic properties with interface defect densities as low as 2⋅1011 cm-2eV-1 have been reported [3]. a-Si:H as an easily producible, large area electronic material is currently used for a variety of different applications, such as displays and solar cells. Organic surface modification of a-Si:H could therefore be an important issue for the fabrication of cheap biosensors based on silicon technology. Further, a-Si:H shows a smaller sensitivity to surface oxidation [4] and Htermination is easier to perform than on crystalline surfaces. The use of a-Si:H films for the fabrication of hydrosilylated silicon surfaces could have the additional benefit of requiring less stringent processing conditions during surface functionalization. In this study, we have modified a-Si:H surfaces by thermally induced hydrosilylation with 1-octadecene and compared their chemical surface properties to those of equally prepared silicon (111) surfaces by XPS investigations. In addition, the electronic properties of hydrosilylated a-Si:H surfaces were investigated by photoconductivity (PC) and spin-dependent photoconductivity (SDPC) measurements.

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