1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: Effect of substrate doping

Abstract
We have studied the electronic properties, in relation to 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 substrates of different types ( n type and p type) and different doping concentrations, from low-doped ( ∼ 10 14 cm − 3 ) to highly doped ( ∼ 10 19 cm − 3 ) . 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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