Creating organic field effect transistors using polymer single crystals.

Research Group: 
Centre for Condensed Matter and Material Physics
Number of Students: 
Length of Study in Years: 
Full-time Project: 
QM Scholarship
Project Description: 
The velocity of carriers in semiconductors will normally be proportional to the electric field driving them. This is the case, for example, for electrons (holes) in the semiconducting channel of a Silicon Field Effect Transistor, FET, where the charge carriers are driven by the source-drain voltage. The density of carriers in the channel is controlled by a third electrode, the gate, separated from the channel by an insulator. Such devices now run much of the electronics so vital to modern technology.
In contrast to these conventional semiconductors, it has been demonstrated that charge carriers in the novel single crystal polydiacetylene, an organic one dimensional semiconductor, coupled with lattice distortions, travel as solitons or solectrons, at around the velocity of sound independent of the driving electric field. Further, the dissipation of these solectrons by phonon scattering is extremely weak and the saturated velocity is reached at very low electric fields. While these materials can’t be doped it should be possible to inject carriers from a suitable source electrode and the polymer chains will act as the channel of a Solectron FET, SFET, with characteristics very different from those of the better known inorganic FETs. Further, the different characteristic would be expected to have important applications in particular power consumption may be drastically reduced as, due to the very low dissipation, very low source-drain voltages could be used to operate these devices.

In this project the ultimate goal is to create a demonstrator SFET and to this end the student will be involved in;
i) Carrying out transient photoconductivity measurements to characterise the defect density on the polymer chains of the polydiacetylene crystals to be used in creation of SFETs.
ii) Investigating potential injecting electrodes that will act to inject carriers into the polydiacetylene and characterising the source-drain channel current as the source-drain voltage is varied.
iii) Creating an insulating layer and gate electrode above the channel and characterising the effect of the gate voltage on ISD.
The above will allow the construction and characterisation of the SFET.
From time to time synthesis of the diacetylene monomer, growth of monomer crystals and the polymerisation of those crystals into polydiacetylene single crystals may be necessary.
The student will gain experience in understanding electron transport properties of a unique material, the one dimensional semiconductor single crystal, polydiacetylene by carrying out characterisation experiments on the crystals using transient photoconductivity techniques. Skills will be gained in the running of an experimental project from the carrying out of experiments to their analysis and testing.Experience will also be gained in the understanding of the operation of organic electronic devices, their characterisation and limitations. In this project the student will learn fabrication techniques valuable in the laboratory in particular creation of complex electrode structures. Electronics will also be learned as the project progresses.
1. K.J.Donovan and E.G.Wilson, “Demonstration of High Mobility One Dimensional Semiconducting Polymers”. J.Phys.C., 123, 4857-4869, (1979).
2. M.G.Velarde, A.P.Chetverikov, W.Ebeling, E.G.Wilson and K.J.Donovan, “On the electron transport in polydiacetylene crystals and derivatives” Europhys. Lett., 106, 27004, 2014.
A good BSc or MSci degree in Physics.
SPA Academics: 
Kevin Donovan