Investigations of niobium carbide contact for carbon-nanotube-based devices

Abstract

Single-walled carbon nanotube (SWCNT) field effect transistors (FETs)with Nb contacts have been fabricated and upon annealing in vacuum at700 °C for 1 h, niobiumcarbide (Nb2C) is formed at the Nb/SWCNT interface. TheNb2C/SWCNT contacts demonstrate a very small Schottky barrier height of ∼ 18 meV(decreased by > 80% relative to that of pristine Nb/SWCNT contact of ∼ 98 meV) to p-type transport. This is attributed to the higher work function ofNb2C (∼5.2 eV) than Nb (∼4.3 eV) and better bondingbetween Nb2C and SWCNTs.The performance of Nb2C-contacted SWCNT FETs is as follows: the p-channel ON current is as high as0.5 µA atVDS = 0.1 V, theION/IOFF ratio is up to ∼ 105 and the subthresholdslope is ∼ 550 mV/dec, which is as good as that of titanium carbide (TiC-) and Pd-contacted SWCNT FETs. Compared withTiC, Nb2C contacts yield more unipolar p-type SWCNT FETs, as a result of theNb2Cs higher work function.More importantly, Nb2C contacts can form near-ohmic contacts to both large-(≥1.6 nm) andsmall-diameter (∼1 nm) SWCNTs, while Pd can only form near-ohmic contacts for large-diameter SWCNTs. Moreover,the Nb2C contacts demonstrate good stability in air.