Controlled growth and electrical properties of heterojunctions of carbon nanotubes and silicon nanowires

Nanometre-scale electronic structures are of both fundamental and technolog ical interest: they provide a link between molecular and solid state physic s, and have the potential to reach far higher device densities than is poss ible with conventional semiconductor technology(1.2). Examples of such stru ctures include quantum dots, which can function as single-electron transist ors(3,4) (although their sensitivity to individual stray charges might make them unsuitable for large-scale devices) and semiconducting carbon nanotub es several hundred nanometres in length, which have been used to create a h eld-effect transistor(5). Much smaller devices could be made by joining two nanotubes or nanowires to create, for example, metal-semiconductor junctio ns, in which the junction area would be about 1 nm(2) for single-walled car bon nanotubes. Electrical measurements of nanotube 'mats' have shown the be haviour expected for a metal-semiconductor junction(6). However, proposed n anotube junction structures(7) have not been explicitly observed, nor have methods been developed to prepare them. Here we report controlled, catalyti c growth of metal-semiconductor junctions between carbon nanotubes and sili con nano,vires, and show that these junctions exhibit reproducible rectifyi ng behaviour.