New Nanoflags, over 2000 Nanometres Long, Promise Improved Electronic Coupling

Researchers are increasingly focused on semiconductor nanowires for advanced electronic and quantum technologies, and a new study details the successful growth and characterisation of indium antimonide (InAsSb) nanoflags. Sebastian Serra, Gaurav Shukla, and Giada Bucci, all from NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, led the investigation, working with colleagues Robert Sorodoc, Valentina Zannier, Fabio Beltram, Lucia Sorba, and Stefan Heun from the same institution. This collaborative effort demonstrates the fabrication of high-quality, free-standing InAsSb nanoflags with tunable composition, exhibiting enhanced Landé g-factors and comparable mobilities to existing InAs and InSb nanowires. Significantly, the observed conductance band pinning suggests a promising pathway for simplified coupling and retention of the desirable quantum properties of InSb, potentially broadening the scope of applications for this material system.

This work details, for the first time, the creation of free-standing InAsSb nanoflags and a comprehensive analysis of their electronic characteristics. Through careful control of growth conditions, researchers fabricated zinc-blende InAsSb nanoflags with varying compositions, with a particular focus on InAs0.77Sb0.23. These nanoflags, measuring approximately 2000±180nm in length, 640±50nm in width, and 130±30nm in thickness, exhibit exceptional promise for next-generation electronic devices. The study reveals that these InAsSb nanoflags possess a Landé g-factor, a measure of spin sensitivity, substantially exceeding that of both indium arsenide (InAs) and indium antimonide (InSb). This enhanced g-factor, alongside comparable electron mobility, suggests a heightened potential for manipulating electron spin, a crucial requirement for quantum information processing. The most impressive measurement from this work is a Landé g-factor of 58.7 ±4.0, a value significantly higher than that found in InAs and InSb, indicating a substantial improvement in spin manipulation capabilities. Measurements conducted on a specific device demonstrate dimensions of (2740 ±20) nm in length, (650 ±10) nm in width, and (94 ±10) nm in thickness, with source-drain contact separation of (1830 ±15) nm and probe contact separation of (900 ±10) nm longitudinally and (300 ±10) nm laterally. These precise dimensions are critical for understanding and optimising device performance. Further investigation reveals evidence of surface Fermi level pinning within the conductance band of the InAs0.77Sb0.23 nanoflags, a behaviour analogous to that observed in InAs. This pinning effect promises to facilitate easier coupling to superconductors, a key requirement for many quantum technologies. Control over antimony incorporation, achieved through varying precursor line pressures, has allowed for the suppression of wurtzite stacking defects when the antimony concentration, denoted as x (InAs1−xSbx), exceeds 10%. Specifically, samples grown with a ratio of group V precursors (TBAs/TDMASb) of 1.5 and an antimony concentration of 15.6% demonstrate pure zinc-blende crystal structure. Au-assisted vapor-liquid-solid (VLS) growth within a chemical beam epitaxy (CBE) system, specifically a Riber Compact-21, served as the foundation for synthesizing InAs-InAsSb heterostructures. Trimethylindium (TMIn), tert-buthylarsine (TBAs), and tris(dimethyamido)antimony (TDMASb) were employed as metal-organic precursors during this process, enabling precise control over material composition. Growth temperature, monitored using both a pyrometer and manipulator thermocouple with an accuracy of ±10°C, was a critical parameter in achieving the desired material properties. The study initially focused on optimising the growth of InAs nanowire (NW) stems, utilising line pressures of 0.35 Torr TMIn and 1.3 Torr TBAs at 390 ±10°C. Following stem growth, the thermocouple-read temperature was increased by ∆T = 50°C to 415±10°C, while continuing stem growth for an additional three minutes. This temperature modulation facilitated the subsequent growth of InAsSb NW segments, initially grown on top of the InAs stems with continuous substrate rotation. This approach allowed researchers to assess the influence of growth parameters on both axial and radial growth without the added complexity of precursor beam directionality. Prior to material deposition, poly-L-lysine was dropcast onto InAs substrates, rinsed with water, and dried with nitrogen to promote adhesion. Gold colloidal nanoparticles, 20nm in diameter and diluted 1:8 in de-ionized water, were then deposited to act as seeds for the VLS growth process. Morphological characterisation of the grown samples was performed using field-emission scanning electron microscopy (SEM) with a Zeiss Merlin instrument, employing a 5kV accelerating voltage and probe current between 90 pA and 100 pA to detect secondary electrons. Crystal structure and chemical composition were further investigated via transmission electron microscopy (TEM) using a JEOL JEM-F200 operated at 200kV, equipped with an EDX spectrometer for elemental analysis. This discovery positions InAsSb nanoflags as a compelling material for building advanced quantum devices and exploring novel spintronic phenomena. The combination of unique electronic properties and ease of integration with superconducting materials opens new avenues for innovation in these rapidly evolving fields. For years, the pursuit of materials exhibiting strong spin-orbit coupling, the interaction between an electron’s spin and its motion, alongside compatibility with existing semiconductor infrastructure has proven elusive. The ability to finely control electron spin is paramount for both quantum computing and spintronics, where information is encoded not just in charge but also in the intrinsic angular momentum of electrons. A higher g-factor translates to greater sensitivity and control over these spins, potentially leading to more stable and efficient quantum bits, or qubits. Crucially, these nanoflags also exhibit electron mobility comparable to that of existing materials like indium arsenide and indium antimonide, meaning they do not sacrifice speed for enhanced spin control. However, translating these promising laboratory results into functional devices remains a considerable undertaking. While the ease of integration with superconductors is encouraging, scaling up production of consistently high-quality nanoflags will be vital. Further research must also focus on understanding the long-term stability of these materials and their behaviour in complex device architectures. The next phase will likely see these nanoflags incorporated into prototype devices, testing their performance in real-world conditions and paving the way for a new generation of quantum and spintronic technologies.