Organic Field-Effect Transistors for Spin-Polarised Transport

Organic Field-Effect Transistors for Spin-Polarised Transport 

Thus it is clear that in order to preserve progress beyond this period, new ideas are required and new technologies have to be established. One approach to this task is based on the concept of manipulation of the spin of electrons, which brings a new degree of freedom to the conventional charge based electronics. This technology of spin-electronics, or spintronics, has been brought more and more into the focus of research in recent years [1]. 

Subsequently, the interest of spintronies researeh aetivities was inereasingly foeused on layer systems with a semieonduetor material instead of the non-magnetie metal. Spin-polarised eleetrons should be injeeted from a ferromagnetie metal into a semieonduetor layer. The large spin-flip length in the semieonduetor materials should be exploited for spin-polarised transport through the semieonduetor layer. One of the first proposals for a spin-polarised transistor originates from Datta and Das [5]. In their eoneept, the externally driven 

Many attempts were made to realise this concept and related ones, most of them based on III-V semieonductor layers like ItiAs or (In,Ga)As with Fe or Co eontaets. However, they brought no convineing demonstration of spin-polarised transport. Instead, their most relevant impaet was a more profound knowledge of the speeifie ehallenges of spin-injeetion and deteetion, which finally resulted in a sueeessful demonstration of spin-polarised transport through semieonduetor layers, based on a distinctly modified injeetion eoncept. 

The essential reason for the failure of spin injeetion from a ferromagnetic metal into a semieonduetor turned out to be the eonduetivity difference between these materials, whieh amounts to several orders of magnitude. It was shown that for the usual parameters of a ferromagnetie metal (i.e. (i) non-eomplete spin-polarisation at the Fermi-level, and (ii) spin-flip length 10 nm) the injeetion of spin-polarised electrons into a semiconductor is prohibited by fundamental laws of eleetrodynamics [6]. This impossibility of spin injection from a ferromagnetic metal into a semiconductor because of its conductance mismateh was derived eonsistently from models, based on electrochemical potential alignment or on a eireuit of parallel conductivity channels for spin-up and spin-down polarisation, respeetively [7]. 

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I 28 Organic Field-Effect Transistors for Spin-Polarised Transport... 

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