Formation of a p-type quantum dot at the end of an n-type carbon nanotube

We use field effect doping to study both electron- (n) and hole- (p) type conduction in a semiconducting carbon nanotube. We find that, in the n-type region, the ends of the tube remain p- type due to doping by the metal contacts. As a result, a p-n junction forms near the contact, creating a small, p-type quantum dot between the p-n junction and the contact. This zero-dimensional quantum dot at the end of a one-dimensional semiconductor is the reduced dimensional analog of the two-dimensional inversion layer that forms at the boundary of a gated three-dimensional semiconductor. (C) 2001 American Institute of Physics.