We report the observation of a thermoelectric power factor in InAs nanowires that exceeds that predicted by a single-band bulk model by up to an order of magnitude at temperatures below about 20 K. We attribute this enhancement effect not to the long-predicted 1D subband effects but to quantum-dot-like states that form in electrostatically nonuniform nanowires as a result of interference between propagating states and 0D resonances.

We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favorable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.

There is currently substantial effort being invested into creating efficient thermoelectric nanowires based on topological insulator chalcogenide-type materials. A key premise of these efforts is the assumption that the generally good thermoelectric properties that these materials exhibit in bulk form will translate into similarly good or even better thermoelectric performance of the same materials

We report a method for growing rectangular InAs nanofins with deterministic length, width and height by dielectric-templated selective-area epitaxy. These freestanding nanofins can be transferred to lay flat on a separate substrate for device fabrication. A key goal was to regain a spatial dimension for device design compared to nanowires, whilst retaining the benefits of bottom-up epitaxial growth. The transferred nanofins were made into devices featuring multiple contacts for Hall effect and fourterminal resistance studies, as well as a global back-gate and nanoscale local top-gates for density control. Hall studies give a 3D electron density 2.5 − 5 × 10 17 cm −3 , corresponding to an approximate surface accumulation layer density 3 − 6× 10 12 cm −2 that agrees well with previous studies of InAs nanowires. We obtain Hall mobilities as high as 1200 cm 2 /Vs, field-effect mobilities as high as 4400 cm 2 /Vs and clear quantum interference structure at temperatures as high as 20 K. Our devices show excellent prospects for fabrication into more complicated devices featuring multiple ohmic contacts, local gates and possibly other functional elements, e.g., patterned superconductor contacts, that may make them attractive options for future quantum information applications.Quantum devices were underpinned for several decades by the interfacial two-dimensional (2D) electron gas found in III-V semiconductor heterostructures. 1 A top-down approach to these systems is costly, with heterostructure complexity limited by interfacial strain issues.Bottom-up approaches have thus generated massive interest with a heavy focus on onedimensional (1D) nanostructures, i.e., nanowires, where small interfaces enable greater heterostructure versatility, including the ability to integrate III-Vs on low-cost Si substrates. [2][3][4] Researcher ingenuity has meant clever new devices still arise from the nanowire geometry even after two decades. That said, we suspect we are not alone in wishing for extra spatial dimensions to work with. An attractive idea would be to take the hexagonal nanowire cross-section and stretch it to obtain a 2D 'nanofin' such that two side-facets have much larger area. These could be transferred to a separate substrate to make devices featuring, e.g., multiple contacts and gates by conventional nanofabrication methods. This concept is impossible with vapor-liquid-solid approaches. 5,6 Here we demonstrate it is possible using selective-area epitaxy, 7,8 giving 2D InAs nanofins with precise size control, and opening a path to more interesting nanostructure shapes via appropriate mask design. 9Our 2D nanofins offer some interesting potential for nanoelectronics. Firstly, they offer