Applied Physics

Intimacy Can Be a Blessing

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Science  07 May 2004:
Vol. 304, Issue 5672, pp. 799
DOI: 10.1126/science.304.5672.799c

When single-walled carbon nanotubes are synthesized, the end product typically consists of a bundled mixture of metallic and semiconducting tubes. For most applications, it would be preferable to isolate one of the nanotube types. In trying to solve an ongoing problem with gallium nitride light-emitting diodes (LEDs), Lee et al. show that this intimate mixture of tubes can be a blessing. Conductivity at the junction between two materials is governed by how well their band structures line up. For n-type GaN, direct contact with the metal works well, but this is not true for p-type GaN. By adding a 100-nm-thick transparent film of carbon nanotubes, they could reduce the contact resistance at the p-GaN junction by a factor of 3, when compared to the directly connected Ni/Au junction. The nanotube layer had the added advantage of increasing the thermal stability of the p junction, making it possible to anneal the n contact with the p junction already in place. This kind of nanotube junction should reduce problems caused by electromigration of atoms in high electric fields, due to the strong bonding of the carbon atoms within the tubes, and the use of this intermediary layer may find application in ZnO-based devices. — MSL

Nano Lett. 10.1021/nl0496522 (2004).

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