  This letter reports a charge transfer p-doping scheme which utilizes
one-electron oxidizing molecules to obtain stable, unipolar carbon nanotube
transistors with a self-aligned gate structure. This doping scheme allows one
to improve carrier injection, tune the threshold voltage Vth, and enhance the
device performance in both the ON- and OFF- transistor states. Specifically,
the nanotube transistor is converted from ambipolar to unipolar, the device
drive current is increased by 2-3 orders of magnitude, the device OFF current
is suppressed and an excellent Ion/Ioff ratio of six order of magnitude is
obtained. The important role played by metal-nanotube contacts modification
through charge transfer is demonstrated.
