Charge injection in conjugated polymers in semiconductor device structures

Abstract

The realisation of interesting electronic properties in materials which can be processed to form useful device structures has provided an important impetus to the field of conjugated polymers, and in recent years much progress has been made in understanding their electronic structure and properties. The semiconductor physics of these polymers is much affected by the ‘one-dimensional’ character of the electronic structure of the polymer. In contrast to three-dimensionally bonded semiconductors, the addition of an extra charge to the structure leads to local reorganisation of the π electron bonding, and to the formation of a self-localised excitation, usually termed a polaron. For the special case of trans-polyacetylene, the excitation is topological, separting regions of the chain with different senses of bond alternation, and is usually termed a solition. The introduction of charge into a semiconductor is traditionally achieved by three routes: chemical doping, photoexcitation of separated electron–hole pairs, and by charge injection to form space-charge or surface-charge layers in semiconductor device structures. We discuss here in particular the last of these, and review the measurements we have carried out on various semiconductor device structures constructed with polyacetylene produced by the Durham precursor route.