Optical excitations of quasi‐one‐dimensional systems: carbon nanotubes versus polymers and semiconductor wires

Abstract

AbstractWe review the main characteristics of optical excitations of semiconductor nanotubes, as obtained from accurate ab‐initio theories and model calculations as well as experimental evidence, and discuss them in light of the previous understanding of other quasi‐one‐dimensional semiconducting systems. We point out striking similarities of nanotubes with III–V quantum wires and conjugated polymers, especially (i) the clear excitonic nature of absorption, very far from the single‐particle behaviour; (ii) its manifestations in optical spectra, where excitonic peaks are accompanied by a strong intensity reduction at the onset of the free‐particle continuum; (iii) the strategies that allow experimental access to exciton binding energies. The recent theoretical and experimental evidence obtained on semiconducting single‐walled nanotubes converges quantitatively to a picture of strongly bound excitons (about 0.3–1.0 eV for nanotubes with 0.4–1.0 nm diameter). We discuss its implications and list a few open issues of relevance to fundamental understanding and optoelectronic applications. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)