Scaling analysis of electron transport through metal-semiconducting carbon nanotube interfaces: Evolution from the molecular limit to the bulk limit

摘要

We present a scaling analysis of electronic and transport properties ofmetal-semiconducting carbon nanotube interfaces as a function of the nanotubelength within the coherent transport regime, which takes fully into accountatomic-scale electronic structure and three-dimensional electrostatics of themetal-nanotube interface using a real-space Green's function basedself-consistent tight-binding theory. As the first example, we examine devicesformed by attaching finite-size single-wall carbon nanotubes (SWNT) to bothhigh- and low- work function metallic electrodes through the dangling bonds atthe end. We analyze the nature of Schottky barrier formation at themetal-nanotube interface by examining the electrostatics, the band lineup andthe conductance of the metal-SWNT molecule-metal junction as a function of theSWNT molecule length and metal-SWNT coupling strength. We show that theconfined cylindrical geometry and the atomistic nature of electronic processesacross the metal-SWNT interface leads to a different physical picture of bandalignment from that of the planar metal-semiconductor interface. We analyze thetemperature and length dependence of the conductance of the SWNT junctions,which shows a transition from tunneling- to thermal activation-dominatedtransport with increasing nanotube length. The temperature dependence of theconductance is much weaker than that of the planar metal-semiconductorinterface due to the finite number of conduction channels within the SWNTjunctions. We find that the current-voltage characteristics of the metal-SWNTmolecule-metal junctions are sensitive to models of the potential response tothe applied source/drain bias voltages.