Electronic states at junctions of molecular semiconductors

We consider properties of junctions for the field effect transistors (FET) geometry where molecular crystals or conducting polymers are used as semiconducting layers. In the molecular crystal Coulomb interaction of free electrons with surface polar phonons of the dielectric layer can lead to self-trapping of carriers and to the formation of a strongly coupled long-range surface polaron. The effect is further enhanced in presence of the bias electric field and strongly depends on the gate dielectric used. In conducting polymers instead of the usual band bending near the contact interface, new allowed electronic bands appear inside the band gap. As a result the bias electric field and the injected charge penetrate into the polymer via creation of the soliton lattice whose period changes with the distance from the contact surface. The current through the contact is performed via moving solitons. (C) 2008 Elsevier Ltd. All rights reserved.