One-dimensional carrier systems in nanowire-based semiconductor heterostructures

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The two major goals of this project are the realization of advanced one-dimensional quantum confined semiconductor heterostructures on an inherently one-dimensional nanowire platform and the correlation of their structural, optical and electrical transport properties.For the growth using molecular beam epitaxy, we pursue two independent routes to implement true quantum confined one-dimensional carrier systems. While the controlled synthesis of quantum-confined two-dimensional quantum wells and zero-dimensional quantum dots has been established recently, one-dimensional quantum wires have remained the final missing element, despite the inherently one-dimensional geometric nature of the nanowire template.Moreover, the paradigm of strain engineering, key for a myriad of devices based on planar heterostructures has to be transferred to nanowires. However, their one-dimensional geometry allows for efficient strain relaxation. Thus, radically new strategies for strain engineering are required to fully exploit the potential of this yet almost unexplored key tuning parameter.Our approach to realize such quantum wires is based on the GaAs-based material systems using (i) diameter-controlled ultra-thin nanowire cores and (ii) radial multi-shell nanowire heterostructures. Such synthesized heterostructure nanowires are characterized on one side with respect to their structural (crystal structure, defects, chemical composition, strain) and their quantized energy spectrum. On the other side, we access the native transport characteristics of different confined carrier systems in the nanowire by optically probing the spatio-temporal carrier dynamics induced by a surface acoustic wave with high spatial and temporal resolution and numerical simulations.Finally, the direct correlation of the results of this contact-less electrical and optical characterization and that of structural investigations will reveal the underlying interconnections between the local microstructural (interface roughness, mixing of different crystal phases, alloy composition, strain) and electrical properties within single nanowires.From these complementary and correlation studies we will derive strategies for the optimization of tailored heterostructure nanowires for device application. In particular, we aim to tailor the valence band structure in these systems by static epitaxial strain. Using acousto-optical spectroscopy we aim to demonstrate a strain-induced light hole ground state with improved electric transport properties arising in a dramatic increase of the hole mobility.