Growth and Transport Properties of InAsSb Nanoflags

The present work reports, for the first time, the growth of high-quality free-standing InAsSb nanoflags and their electronic properties. Different growth conditions have been explored, and zinc-blende InAsSb nanoflags of various composition have been obtained. In particular, InAs0.77Sb0.23 nanoflags are on average (2000+-180) nm long, (640+-50) nm wide, and (130+-30) nm thick. We show that these nanoflags have a Landé g-factor larger than InAs and InSb and a mobility comparable to those of the best performing InAs and InSb nanoflags. Besides, we show evidence for a surface Fermi level pinning in the conductance band of these InAs0.77Sb0.23 nanoflags, similar to the well-known behavior of InAs. This promises to make InAsSb easy to couple to superconductors, while keeping or improving many of the features that make InSb an interesting material for quantum applications.

💡 Research Summary

The manuscript reports the first successful synthesis of free‑standing InAs₁₋ₓSbₓ nanoflags (NFs) with high crystalline quality and a comprehensive characterization of their structural, compositional, and electronic properties. Using Au‑catalyzed vapor‑liquid‑solid (VLS) growth in a chemical beam epitaxy (CBE) system, the authors first grow InAs nanowire (NW) stems on InAs(111)B substrates. After establishing the stems, the substrate rotation is stopped and the orientation is adjusted via reflection high‑energy electron diffraction (RHEED) so that one {112} sidewall faces the TBAs (tert‑butylarsine) beam. By carefully tuning the line‑pressure ratio r = p_TBAS/p_TDMASb of the group‑V precursors, they control antimony incorporation, crystal phase, and defect density. The optimal conditions (r ≈ 1.5, TMIn = 0.7 Torr, TBAS = 1.1 Torr, TDMASb = 0.9 Torr) yield nanoflags with an average length of 2000 ± 180 nm, width of 640 ± 50 nm, and thickness of 130 ± 30 nm, corresponding to a composition of InAs₀.₇₇Sb₀.₂₃ (53 % In, 36 % As, 11 % Sb by EDX). Transmission electron microscopy shows essentially defect‑free zinc‑blende (ZB) crystal structure, with only a single stacking fault at the stem‑NF interface, consistent with previous reports on InSb nanoflags.

Electrical transport is investigated on individual nanoflags fabricated into Hall‑bar devices on a Si/SiO₂ global back‑gate. Four‑probe measurements at 2.7 K and 0.44 K reveal n‑type behavior with a conductance that never fully pinches off even at V_bg = ‑40 V, indicating a surface conduction channel due to Fermi‑level pinning in the conduction band—a phenomenon well known for InAs. The conductance exhibits hysteresis attributed to charge traps at the semiconductor‑gate interface.

From the linear region of the G_xx–V_bg curve (‑30 V to ‑20 V) the field‑effect mobility is extracted as μ_FE ≈ 2.2 × 10⁴ cm² V⁻¹ s⁻¹ at 2.7 K. Hall measurements give a Hall mobility μ_H ≈ 6.0 × 10⁴ cm² V⁻¹ s⁻¹ at 0.44 K, values that are comparable to or exceed the best reported for pure InAs or InSb nanoflags. Carrier densities extracted from the Hall slope range from ~10¹⁶ cm⁻³ to ~10¹⁸ cm⁻³ depending on gate bias, confirming the presence of a high‑density surface channel.

Magnetotransport analysis of Shubnikov‑de Haas oscillations yields an effective Landé g‑factor |g*| = 58.7 ± 4.0, significantly larger than that of bulk InAs (≈14.7) and InSb (≈50). This large g‑factor, together with the strong spin‑orbit coupling inherent to the InAsSb alloy, makes these nanoflags attractive for topological superconductivity and Majorana zero‑mode experiments, where a high g‑factor reduces the magnetic field required to enter the topological regime.

The combination of (i) high electron mobility, (ii) a large g‑factor, and (iii) surface Fermi‑level pinning in the conduction band provides a favorable platform for hybrid superconductor–semiconductor devices. The surface pinning ensures good transparency at S‑Sm interfaces, while the high mobility and tunable g‑factor enable precise electrostatic control of the subband occupation and spin texture. Consequently, InAs₀.₇₇Sb₀.₂₃ nanoflags emerge as a versatile building block for spin‑orbit qubits, gate‑tunable Josephson junctions, and Majorana nanowire networks, potentially surpassing the performance of existing InAs or InSb nanostructures. The work thus opens a new pathway for engineering III‑V alloy nanostructures with tailored electronic properties for next‑generation quantum technologies.