Martin Luther University Halle-Wittenberg

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Diploma Thesis

Electronic Transport Properties of Ferroelectric Tunnel Junctions

Goal of the work was the investigation on the electronic transport properties of tunneljunctions with a ferroelectric insulating barrier, in our case either BaTiO3 or PbTiO3. Motivated by fundamental experiments by CONTRERAS (Contreras et al. Applied Physics Letters (2003) vol. 83 (22)) and GAJEK (Gajek et al. Nature Materials (2007) vol. 6) we mainly concentrated on the asymmetry of the conductance for the different polarization states of the barrier - this effect is called tunneling electroresistance (TER). Based on an idea of ZHURAVLEV (Zhuravlev et al. Physical Review Letters (2005) vol. 94 (24)) we developed a model based on the complex bandstructure of the barrier material and the macroscopic properties of the electrodes, which provides useful informations on the electronic transport through a ferroelectric tunneljuction (FTJ). The ab-initio calculations of the electronic structure were done in the framework of the density functional theory (DFT) in a local density approximation (LDA) using different KORRINGA-KOHN-ROSTOKER methods (layered and screened KKR). The presented results depict the influence of several material parameter on the electronic transport properties of the FTJ. We focussed especially on the dependency of the TER on the charge screening properties of the electrodes, different strenghts of the barriers electric polarization, as well as on different FERMI-energies for the transport electrons. In succession we could explain why and where the TER is maximized. Furthermore we are giving promising indications why the TER might change sign for different FERMI-energies. The results were mainly discussed by means of the complex bandstructures.

Diploma Thesis (German)
diplomarbeit_hinsche_comp.pdf (14.9 MB)  vom 09.02.2010