2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Electrical Contacts to Nanotubes and Nanowires: Why Size Matters

F. Leonard and A.A. Talin
Sandia National Laboratories, US

Keywords:
carbon nanotube, nanowire, electrical contacts

Abstract:
Electrical contacts play a key role in electronics. As new materials such as nanotubes and nanowires are explored for nanoelectronics, the fundamental aspects of electrical contacts need to be re-examined due to the unique properties of these nanostructures. Recent experimental work has indicated that the diameter of the carbon nanotube plays a crucial role in determining the contact properties, with a transition from Schottky to ohmic behavior as the diameter is increased. These experiments also show that the type of metal used can significantly affect the contact quality. In this talk, recent theoretical and modeling results addressing these issues will be presented. We find that for quasi-one dimensional (Q1D) structures such as nanotubes and nanowires, contact with the metal only leads to weak band realignment, in contrast with bulk metal-semiconductor contacts. Schottky barriers decrease with nanotube diameter and eventually become negative for Pd. For Q1D structures in general, the barriers are much reduced compared with the bulk limit, and should facilitate the formation of good contacts. However, the conventional strategy of heavily doping the semiconductor to obtain Ohmic contacts breaks down as the nanowire diameter is reduced. The issue of Fermi level pinning will also be addressed, and it will be shown that the unique density of states of Q1D structures makes them less sensitive to this effect. The results agree with the recent experimental work, and should apply to a broad range of Q1D materials.

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