Stefan Thiel
Study of Interface Properties in LaAlO_3/SrTiO_3 Heterostructures
Supervisor: Prof. Dr. Jochen Mannhart [Experimental physics VI]
Date of oral examination: 02/19/2009
135 pages, english
Interface effects, which e.g. play a crucial role in semiconductors, are also important in oxides. In this work the interface between the two oxides Lanthanumaluminate (LAO) and Strontiumtitanate (STO) is investigated. Both materials are band-insulators, however a conducting layer can form at the interface, a so called quasi-two-dimensional electron gas (q2-DEG). After a brief introduction to this heterostructure the sample-preparation and characterization is described, and subsequently different projects are reported in detail. The investigation of the electronic transport properties as a function of the LAO film thickness revealed a transition from insulating to conducting behavior if the films exceed a critical thickness of 3 unit cells (uc). By electric field effect the conductivity of the interface can be tuned to a large extent. In samples with 3 uc of LAO a metal-insulator-transition can be induced. To be able to investigate defined structures a novel patterning technique was developed in the course of this thesis, which is based on the variation of the thickness of the epitaxial LAO. At 200 mK the q2-DEG condenses into a superconducting ground state. Investigations on bicrystalline samples reveal that the conducting interface is strongly influenced by dislocations in the STO substrate.