Organophosphonates as model system for studying electronic transport through monolayers on SiO₂/Si surfaces

We report electrical transport measurements made on alkylphosphonate self-assembled monolayers grown on nanometer-thin SiO₂ on top of highly p-doped silicon. At small bias direct tunneling is characterized by a decay constant of β ≈ 0.7/carbon. At larger positive bias to the silicon (1.1-1.5 V) the current-voltage traces feature a prominent shoulder, reminiscent of a negative differential resistance. We attribute this feature to a significant reduction in trap-assisted tunneling, as supported by a simulation. Hence, organophosphonate monolayers are excellent model systems to study electrical transport through ordered structures; they also provide highly efficient electrical passivation of the SiO₂/Si surface.