Investigations of Carbon Nanotube Based Electronic Devices with Focus on Metal and Carbon Nanotube Contacts

Abstract

In this dissertation, we have investigated carbon nanotube (CNT), both single wall (SW) and double wall (DW), based devices such as field effect transistors (FETs) and diodes, with the focus on CNT-metal contacts. High performance p-type SWCNT FETs with near ohmic source/drain contact to SWCNT of diameter as low as 1.0 nm has been achieved with Niobium (Nb) carbide contact, formed between SWCNT and Nb by means of thermal solid state reaction. It has also been found that thin film transistor based on random network of SWCNTs (rn-SWCNTs) can overcome the processing challenges of SWCNT FET, e.g., precise position and alignment of CNT. Using low work function metal Yttrium as the source/drain contacts, high performance n-type rn-SWCNT FETs have been realized. Furthermore, SWCNT Schottky diode has been fabricated by asymmetrically modifying the Schottky barriers at the SWCNT-gold contacts using thiolate methanethiol (CH&#8323SH) and trifluoroethanethiol (CF&#8323CH&#8322SH). In addition to the study on CNT-metal contact, the transport properties of double wall CNT with both semiconducting tubes (s-s DWCNT) have been investigated and this has shown that the inter-tube interaction in s-s DWCNT is dependent on the diameter of DWCNT. In general, the conductance of s-s DWCNT is larger than that of SWCNT with the same diameter as a result of inter-tube interaction. However, when the tube diameter is very small (<1.6 nm), the bandgap of s-s DWCNT is greatly reduced owing to the p-s rehybridization of the even smaller inner tube.