CPM Seminar

Charge Transferred Doping and Electrically-induced IR Emission in Carbon Nanotube Transistors

Jia Chen

IBM Watson Research Center

Significant progress has been made recently on carbon nanotube based field effect transistors(CNTFET), in terms of understanding both their scaling and performance limits. However, the Schottky barriers (SB) between the CNT and the metal contacts lead to low drive current, undesirable subthreshold characteristics, and strong ambipolar conduction when the transistor is scaled down vertically, all unacceptable in logic gate applications. We report on chemical doping schemes utilizing molecules and a charge transfer mechanism to obtain self-aligned, stable and unipolar CNTFETs to meet the performance challenges. We demonstrate an ability to change carrier injection properties; and to improve device performance in both ON- and OFF-states. Using ambipolar CNTFETs with appropriate biasing we can inject electrons and holes simultaneously from the source and drain of the nanotube, and observe radiative e-h recombination from individual CNTs. CNTFETs provide a novel form of molecular light source that requires neither external doping nor well defined space charge region as in conventional LEDs. CNFETs being three-terminal devices allow the tuning of not only the intensity of electroluminescence, but also the position along the length of the CNT from which the emission originates. Thus the recombination region can be translated over large distances (tens of microns) in long CNTs by varying the gate potential. Such experiments provide new insights into the transport processes in carbon nanotubes. They allow us to follow the fronts of the electron and hole currents under varying bias conditions, determine the recombination lengths and recombination times, observe defects, etc.