Quantum Transport Characterizations in Selective-Area Grown InGaAs Nanowire Networks

Selective-area-grown (also referred to as ‘templated’) semiconductor nanostructures have gen- erated considerable research interest in recent years as potential vehicles for the investigation of fundamental quantum phenomena as well as towards scalable networks for deployment in future quantum computers. Such structures made from III-V semiconductors, which can play host to effects such as strong spin-orbit interaction and Fermi-level pinning of the conduction band at the interface, are of interest due to the fast spin precession as well as being potential vehicles for realization of non-trivial topological states of matter. This nascent technology has relied on the bridging of growth techniques, nano-fabrication, low-temperature electronic transport studies, and compositional analysis during its development. The required expertise involved has resulted in fruitful collaborations between a number of re- search groups in different institutions, which has enabled steady progress. Devices have been fabricated on quasi-1D nanostructures comprised of InGaAs nanowires grown atop defect-free GaAs nanomembranes, first with bulk-doping of Si + donors in the InGaAs wires in order to demonstrate a proof-of-principle for the system. Later, devices utilizing modulation doping strategies in order to reduce impurity scattering - while still providing the necessary additional carriers for transport - have been realized, measured, and analysed. Devices with branched geometries have been produced and quantum intereference effects have been observed across the junctions. Important transport parameters such as mean free paths, coherence lengths and spin-orbit lengths have been extracted in order to characterize the structures and motivate the next steps along the evolution of the systems. Novel fabrication techniques have been developed and employed in order to investigate and control various aspects of the structures, including carrier density and electric fields across the wires