ABSTRACT
ABSTRACT: Conjugated polymers which can be processed to form fully dense thin films can be used as the active component in conventional semiconductor device structures such as the MISFET. Devices of this type can show low densities of defects states within the gap, and we discuss how this may be the case for these polymeric materials which clearly show considerable disorder At a microscopic level it is necessary to consider the role of self localisation of carriers injected onto the chains to form polarons (or for the case of trans-polyacetylene, solitons). This self-trapping of charge onto a specific chain is disadvantageous for charge transport; the rate limiting step for electronic conduction is set by interchain charge transfer which is a thermally activated process, and mobilities are typically very low, of order 10-4 cm2V-1s-1. However, within these self-trapped excitations there is considerable reorganisation of the π-electron structure, and states are pushed from the conduction and valence bands into the semiconductor gap, giving rise to large changes in the sub-gap optical absorption.. This gives novel electro-optical behaviour for devices fabricated with conjugated polymers, with control of the sub-gap absorption through for example the charge density within the accumulation layer in an MIS or MISFET structure.
