High-quality vertically aligned InAs nanowires grown by molecular-beam epitaxy using Ag-In alloy segregation.

InAs nanowires show important potential applications in novel nanoelectronic devices, infrared optoelectronic devices and quantum devices, and all these applications require controllable growth of the InAs nanowires. However, the growth direction of metal-assisted InAs nanowires on Si substrates is often random. Here, we develop a new approach to grow vertically aligned InAs nanowires on Si (111) substrates by molecular-beam epitaxy using Ag as catalysts. The vertically aligned one-dimensional InAs nanowires are grown on the parasitic two-dimensional InAs film on the Si substrates by using the Ag nanoparticles segregated from Ag-In alloy catalysts. The diameters of the vertically aligned InAs nanowires obtained by this method are mainly distributed between 20 and 50 nm. Detailed transmission electron microscope data show that the nanowires with thinner diameters tend to have less stacking faults and twin defects and high crystal quality pure wurtzite nanowires can be obtained. Using these vertically aligned InAs nanowires as the channel material of field effect transistors, we have obtained a field-effect mobility of ∼2800 cm2V-1s-1and anIon/Ioffratio of ∼104at room temperature. Our work provides a new method for the controlled growth of high-quality vertically aligned InAs nanowires on Si substrates.

Selective area growth of in-plane InAs nanowires and nanowire networks on Si substrates by molecular-beam epitaxy.

In-plane InAs nanowires and nanowire networks show great potential to be used as building blocks for electronic, optoelectronic and topological quantum devices, and all these applications are keen to grow the InAs materials directly on Si substrates since it may enable nanowire electronic and quantum devices with seamless integration with Si platform. However, almost all the in-plane InAs nanowires and nanowire networks have been realized on substrates of III-V semiconductors. Here, we demonstrate the selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates. We find that the selectivity of InAs growth on Si substrates is mainly dependent on the growth temperature, while the morphology of InAs nanowires is closely related to the V/III flux ratio. We examine the cross-sectional shapes and facets of the InAs nanowires grown along the 〈110〉, 〈100〉 and 〈112〉 orientations. Thanks to the non-polar characteristics of Si substrates, the InAs nanowires and nanowire networks exhibit superior symmetry compared to that grown on III-V substrates. The InAs nanowires and nanowire networks are zinc-blende (ZB) crystals, but there are many defects in the nanowires, such as stacking faults, twins and grain boundaries. The crystal quality of InAs nanowires and nanowire networks can be improved by increasing the growth temperature within the growth temperature window. Our work demonstrates the feasibility of selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates.

Plateau Regions for Zero-Bias Peaks within 5% of the Quantized Conductance Value 2e

Probing an isolated Majorana zero mode is predicted to reveal a tunneling conductance quantized at 2e^{2}/h at zero temperature. Experimentally, a zero-bias peak (ZBP) is expected and its height should remain robust against relevant parameter tuning, forming a quantized plateau. Here, we report the observation of large ZBPs in a thin InAs-Al hybrid nanowire device. The ZBP height can stick close to 2e^{2}/h, mostly within 5% tolerance, by sweeping gate voltages and magnetic field. We further map out the phase diagram and identify two plateau regions in the phase space. Despite the presence of disorder and quantum dots, our result constitutes a step forward toward establishing Majorana zero modes.

Suppressing Andreev Bound State Zero Bias Peaks Using a Strongly Dissipative Lead.

Hybrid semiconductor-superconductor nanowires are predicted to host Majorana zero modes that induce zero-bias peaks (ZBPs) in tunneling conductance. ZBPs alone, however, are not sufficient evidence due to the ubiquitous presence of Andreev bound states. Here, we implement a strongly resistive normal lead in InAs-Al nanowire devices and show that most of the expected Andreev bound state-induced ZBPs can be suppressed, a phenomenon known as environmental Coulomb blockade. Our result is the first experimental demonstration of this dissipative interaction effect on Andreev bound states and can serve as a possible filter to narrow down the ZBP phase diagram in future Majorana searches.

Foreign-catalyst-free GaSb nanowires directly grown on cleaved Si substrates by molecular-beam epitaxy.

We have successfully fabricated foreign-catalyst-free GaSb nanowires directly on cleaved Si (111) substrates by molecular-beam epitaxy. We find that GaSb nanowires with the absence and presence of Ga droplets at the tip can be simultaneously obtained on cleaved Si substrates without Ga pre-deposition. Systematic morphological and structural studies verify that the two kinds of nanowires presented have different growth mechanisms, which are vapor-solid and vapor-liquid-solid mechanisms. The growth of GaSb nanowires can also be achieved on cleaved Si (110) and Si (100) substrates. The cleavage plane of the Si substrate has an obvious influence on the growth of the GaSb nanowires. The growth direction and crystal quality of catalyst-free nanowires are independent of the cleavage plane of the substrate. Our results may facilitate the understanding of the growth mechanism of III-V nanowires and the integration of foreign-catalyst-free GaSb nanowire-based devices with mature semiconductor technology.

Silver-assisted growth of high-quality InAs1- x Sb x nanowires by molecular-beam epitaxy.

InAs1-x Sb x nanowires show promise for use in nanoelectronics, infrared optoelectronics and topological quantum computation. Such applications require a high degree of growth control over the growth direction, crystal quality and morphology of the nanowires. Here, we report on the silver-assisted growth of InAs1-x Sb x nanowires by molecular-beam epitaxy for the first time. We find that the growth parameters including growth temperature, indium flux and substrate play an important role in nanowire growth. Relatively high growth temperatures and low indium fluxes can suppress the growth of non-[111]-oriented nanowires on Si (111) substrates. Vertically aligned InAs1-x Sb x nanowires with high aspect ratios can be achieved on GaAs (111)B substrates. Detailed structural studies suggest that high-quality InAs1-x Sb x nanowires can be obtained by increasing antimony content. Silver-indium alloy segregation is found in ternary alloy InAs1-x Sb x nanowires, and it plays a key role in morphological evolution of the nanowires. Our work provides useful insights into the controllable growth of high-quality III-V semiconductor nanowires.

Large-Composition-Range Pure-Phase Homogeneous InAs1-xSbx Nanowires.

Narrow bandgap InAs1-xSbx nanowires show broad prospects for applications in wide spectrum infrared detectors, high-performance transistors, and quantum computation. Realizing such applications requires a fine control of the composition and crystal structure of nanowires. However, the fabrication of large-composition-range pure-phase homogeneous InAs1-xSbx nanowires remains a huge challenge. Here, we first report the growth of large-composition-range stemless InAs1-xSbx nanowires (0 ≤ x ≤ 0.63) on Si (111) substrates by molecular beam epitaxy. We find that pure-phase InAs1-xSbx nanowires can be successfully obtained by controlling the antimony content x, nanowire diameter, and nanowire growth direction. Detailed energy dispersive spectrum data show that the antimony is uniformly distributed along the axial and radial directions of InAs1-xSbx nanowires and no spontaneous core-shell nanostructures form in the nanowires. On the basis of field-effect measurements, we confirm that InAs1-xSbx nanowires exhibit good conductivity and their mobilities can reach 4200 cm2 V-1 s-1 at 7 K. Our work lays the foundation for the development of InAs1-xSbx nanowire optoelectronic, electronic, and quantum devices.