Condensed Matter Seminar Series

Carbon Nanotube Electronics and Optoelectronics

Phaedon Avouris

IBM

Thursday April 14, 11:30 am, Room 234, Physics Building

Abstract: Carbon nanotubes (CNTs) have properties that make them ideal for applications in nano- and opto-electronics. Particular emphasis has been placed on the fabrication and optimization of CNT field-effect transistors (CNTFETs) with very promising results. However, some problems remain. Charge-transfer at the CNT-metal interfaces can lead to the formation of Schottky barriers, which adversely affect the performance of the FET. Another problem appears upon scaling of the gate insulator thickness (tox). At small tox, unipolar CNTFETs turn ambipolar with large off currents. We were able to eliminate these problems by chemical, or electrostatic doping of the contact regions. The resulting unipolar CNTFETs have outstanding operational characteristics.
While ambipolar (a-) CNTFETs may be undesirable in logic applications, they can be particularly valuable in photonics. Earlier we have shown that when electrons and holes are injected from the opposite terminals of an a-CNTFET, a fraction of them recombine radiatively generating an electrically-excited single nanotube light source. Unlike conventional p-n diodes, however, a-CNTFETs are not doped and there is no fixed p-n interface. Through spatially resolved measurements we will show that the emission can be translated along the CNTFET channel by varying the gate voltage. Study of the properties of the emission as a function of applied bias provides new insights on the electrical transport in CNTs. Stationary light spots are also observed and their generation mechanism will be discussed. Finally, single CNT photoconductivity spectra and theoretical modeling will be used to prove the excitonic nature of the excited states of the CNTs.