MBE growth and characterization of InAs/GaSb core/shell nanowire arrays

III-V semiconductor compounds InAs and GaSb are almost lattice matched and when incontact, the heterostructure appears to have a broken gap alignment at their interface[1].In a core/shell nanowire (NW) geometry, these particularities make this combination interestingfor low power electronic devices (Tunneling Field Effect Transistors) as well as thestudy of fundamental physical properties such as quantum effects arising due to electroninterference. This thesis reports on the MBE growth as well as the structural and electricalcharacterization of InAs/GaSb NW arrays.For the growth, a Si(111) substrate is covered with a thin thermal SiO2 film in whichtwo-dimensional, periodic arrays of nano-sized holes are patterned. The InAs NW growth isoptimized regarding the yield and morphology of the wires. Substrate preparation therebyis crucial for achieving a high NW yield. The subsequent growth of the GaSb shell hasbeen investigated and optimum growth conditions have been achieved. The effect of dopingof the GaSb shell and substrate temperature, during shell deposition, is also studied.NW morphology and structural characteristics have been investigated. The small latticemismatch between InAs and GaSb combined with the one-dimensional geometry result in amisfit dislocation free coreshell NW hetero-interface.Post-growth, the GaSb shell is etched from part of the NW to have access to the InAscore in order to study the transport at the hetero-junction. Dry and wet etching techniquesprovide different results, both of which can be used for fabricating NW devices. Metalliccontacts have been fabricated on different parts of these partially etched core/shell NWs aswell as on non-etched wires. This process is optimized for the dimensions of these core/shellNWs with respect to reproducibility.Electrical characterization includes gate dependent measurements, which have been carriedout at room temperature as well as at low temperatures down to 1.5K using a cryogenicsetup. Magneto-transport measurements are used to probe electron transport in thesenanoscopic systems. Characterization therefore includes the observation of quantum mechanicalelectron interference effects probed at different temperatures and different anglesof the magnetic field with respect to the NW axis. Analysis on this data includes approximationsof typical figures of merit like the phase coherence length or the elastic mean freepath but also includes a proper analysis of the size and possible locations of the electroninterference loops

Cryogenic multiplexing using selective area grown nanowires

Abstract Bottom-up grown nanomaterials play an integral role in the development of quantum technologies but are often challenging to characterise on large scales. Here, we harness selective area growth of semiconductor nanowires to demonstrate large-scale integrated circuits and characterisation of large numbers of quantum devices. The circuit consisted of 512 quantum devices embedded within multiplexer/demultiplexer pairs, incorporating thousands of interconnected selective area growth nanowires operating under deep cryogenic conditions. Multiplexers enable a range of new strategies in quantum device research and scaling by increasing the device count while limiting the number of connections between room-temperature control electronics and the cryogenic samples. As an example of this potential we perform a statistical characterization of large arrays of identical quantum dots thus establishing the feasibility of applying cross-bar gating strategies for efficient scaling of future selective area growth quantum circuits. More broadly, the ability to systematically characterise large numbers of devices provides new levels of statistical certainty to materials/device development