Photocurrents in topological insulator nanowire and Hall bar devices Dissertation Festkörperphysik Photoströme topologische Isolatoren Seebeck effect nanowire photocurrent spin polarized current topological insulator In this thesis the transport properties of topological insulators are investigated. In contrast to trivial insulators topological insulators possess conducting boundary states which cross the bulk energy gap that separates the highest occupied electronic band from the lowest unoccupied band. The materials used in this thesis are three dimensional topological insulators with time reversal symmetry. Their associated helical surface states are protected against elastic backscattering by Kramers degeneracy. The unique properties of the helical surface states can be utilized to generate spin polarized currents at the surface of topological insulators and to control their propagation direction. This makes them a promising material class for the field of spintronics. Here we perform photocurrent scans of topological insulator Hall bar and nanowire devices. From these measurements we obtained two dimensional maps of the polarization independent and helicity dependent components of the photocurrents. We find that the polarization independent component is dominated by the Seebeck effect and thus driven by thermoelectric currents. On the other hand the helicity dependent component is driven by the spin polarized currents that emerge from the topologically non trivial helical surface states via the circular photogalvanic effect. First and foremost our experiments demonstrate that topological insulator nanowires provide a promising platform for the generation of spin polarized ...