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

TL;DR

This study investigates how substrate doping levels influence the structural and electronic properties of 1-octadecene monolayers on hydrogen-terminated silicon surfaces, revealing doping-dependent variations in packing density and electrical insulation performance.

Contribution

It provides new insights into how different silicon doping types and concentrations affect monolayer formation and properties, highlighting the importance of surface potential and Fermi level position.

Findings

Monolayers on n-, p-, and p+ silicon are densely packed and good insulators.

Monolayers on n+-type silicon are more disordered with higher leakage currents.

Surface potential and Fermi level position are crucial for monolayer chemisorption.

Abstract

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 (~1E14 cm-3) to highly doped (~1E19 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 ~1E-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 (>1E-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.