Quantitative Experimental Analysis of Schottky Barriers and Poole–Frenkel Emission in Carbon Nanotube Devices

In this paper, we investigated carbon nanotube FETs (CNT FETs) utilizing semiconducting single-walled CNTs (SWCNTs). Multiple devices, each of different metal source and drain contacts, were fabricated on a single SWCNT. Over specific temperature regimes, transport properties of the devices were found to be consistent with the Bethe theory of thermionic emission for Schottky contacts, and the Poole-Frenkel emission was dependent on the device position. As was expected, transport from thermionic emission over the barrier was found to be the dominant mechanism. Barriers of 25-41 meV were present, as found by activation energy analysis for temperatures ranging from 20 to 300 K for the devices. A Schottky diode was also fabricated on a separate nanotube using an ohmic contact at the Pd source and a Schottky contact for the Ag drain electrode. Assuming the same physical assumptions for an Si semiconductor device, the results indicate an ideality factor greater than 2, Schottky barrier of ~0.37 eV, and image charge lowering of ~0.1 eV.