Low contact resistance in carbon nanotube devices: metal-induced gap states

Designing devices with low contact resistance, especially those based on carbon-based materials, is becoming increasingly important. In this work, we investigated the electronic structure and transport properties of two-types of structures based on carbon nanotubes connecting graphene electrodes by combining density functional theory with the non-equilibrium Green's function method. The directly connected structure exhibits ohmic contact and has a lower contact resistance compared to the typical van der Waals-connected structure. Furthermore, a metal-induced gap state in the directly connected structure provides an extra transport channel, making electron travel easier. The two structures have around a 4-order-of-magnitude difference in conductance at equilibrium and a 5-order-of-magnitude difference in contact resistance at a bias voltage of 0.4 V. This work may offer basic predictions for carbon nanotube transport as well as novel concepts for designing carbon nanotube transistors.