1-octadecene monolayers on Si(111)hydrogen-terminated surfaces:Effect of substrate doping
2008/04/30 14:14
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We have studied the electronic properties, in relation to their structural properties, of monolayers of 1-octadecene attached on a hydrogen-terminated (111) silicon surface. The molecules are attached using the free-radical reaction between C=C and Si-H activated by an ultraviolet illumination. We have compared the structural and electrical properties of monolayers formed on silicon substrate of different types (n-type and p-type) and different doping concentrations from low-doped (~1014 cm-3) to highly doped (~1019 cm-3) silicon substrates. We show that the monolayers on n-, p- and p+-silicon are densely packed and that they act as very good insulating films at a nanometer thickness with leakage currents as low as ~10-7 A.cm-2 and high quality capacitance-voltage characteristics. The monolayers formed on n+-type silicon are more disordered and therefore exhibit larger leakage current densities (>10-4 A.cm-2) when embedded in a silicon/monolayer/metal junction. The inferior structural and electronic properties obtained with n+-type silicon pinpoint the important role of surface potential and of the position of the surface Fermi level during the chemisorption of the organic monolayers.
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1-octadecene monolayers on Si(111)hydrogen-terminated surfaces:Effect of substrate doping
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