THE SEMICONDUCTOR DEVICE PHYSICS OF POLYACETYLENE

BURROUGHES and R. H. FRIEND Cavendish Laboratory Madingley Road Cambridge CBS OHE UK. 

The metallic properties of the heavily-doped polymers provided the initial focus of interest in the electronic properties, but the theoretical framework for the modelling of the electronic excitations due to Rice [5] and Su et al [6], which for the case of trans-polyacetylene take the form of solitary-wave excitations of the chain, has broadened the area of interest to cover, in particular, the optical and non-linear optical properties of this class of polymos. 

Experimental work on polyacetylene has been primarily carried out with polymer prepared via the Shirakawa route or modifications of it This material has an open, fibrillar morphology (with up to 2/3 voids) and is very well suited for rapid doping, achieved either chemically or electrochemically. It is however, much less suited for many of the measurements of the semiconductor properties, and is not readily used within device structures. An alternative route for the synthesis of polyacetylene, developed by Edwards 

Hguie 1 The Durham route to polyacetylene. Monomer (A) is polymerised to the precursor polymer (B) which is processed from solution and is converted to polyacetylene by thermal elimination of hexafluoro-orthoxylene, initially to cu-rich and that to all trans iscnner. 

We have found that the polymer prepared in this way is very well suited for use in semiconductor device structures in which a semiconductor of one carrier type only is required (unipolar devices). The polymer as prepared is extrinsically doped with p-type carriers, to a concentration in the range lO to 10 8 cm 3, and these dopants are not readily mobile under the applied electric fields within these structures. We have made and measured Schottky-barrier diodes, MIS (Metal Insulator Semiconductor) diodes and MISFETs (MIS Field Effect Transistors), and it is the results of these investigations, some of which are published elsewhere [11-17], which are presented in the present chapter. 

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Burroughes, J.H. and Friend, R.H., The semiconductor device physics of polyacetylene. In Conjugated polymers, ed. J.L. Bredas and R. Silbey, Kluwer, Dordrecht, The Netherlands, 1991, 555-622. 

Burroughes, J.H. Friend, R.H., "The Semiconductor Device Physics of Polyacetylene", p.555 in Br6das, J.L. Silbey, R. (Eds.), Conjugated Polymers The Novel Science and technology of Highly Conducting and Nonlinear Optically Active Materials, Kluwer Academic Publishers, Norwell, MA, USA (1991). 

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