Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

7Electrical Properties ofSemiconductor NanocrystalsDavid S. Ginger and Neil C. GreenhamCavendish Laboratory, Cambridge, EnglandI. INTRODUCTIONThe size-dependent optical properties of semiconductor nanocrystals havebeen extensively studied, as described elsewhere in this volume. In thischapter, we concentrate instead on the electrical properties of nanocrystals.We show how electrons can be injected into nanocrystals, transported betweennanocrystals and transferred between nanocrystals and organic molecules.We then describe the potential applications of nanocrystals in electronicand optoelectronic devices. We attempt to give an overview of the field,although we cannot mention all of the articles which have been published inthis diverse and expanding area. We draw many of our examples from ourown work and from the work of those other groups with which we happen tobe most familiar. We restrict ourselves to chemically synthesized semiconductornanocrystals and concentrate mostly on II–VI nanocrystals such asCdSe in the size regime of less than 10 nm, where quantum confinement effectsare important.In a nanocrystal, the electronic states are typically confined within thenanocrystal by significant potential barriers. Transport between nanocrystalscan, therefore, be considered as a problem of hopping between localizedstates. For small nanocrystals in the strong confinement regime, charge transportis limited by interparticle electron transfer, rather than by the transportof electrons within a single particle. Therefore, the physics has more in commonwith that of charge transport in molecular systems, rather than withtraditional semiconductor transport theory. In nanocrystals, changing theCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.