Growth and Transport Properties of InAsSb Nanoflags

TL;DR

The paper addresses creating high-mobility, composition-tunable InAsSb nanoflags for quantum applications by growing free-standing, zinc-blende nanoflags via Au-assisted VLS growth in chemical beam epitaxy. It reports InAs0.77Sb0.23 nanoflags with mean dimensions around 2000 × 640 × 130 nm, exhibiting field- and Hall-mobilities near $2.2\times10^{4}$ cm$^2$/Vs and strong spin splitting, with a measured $|g^*| ≈ 58.7 ± 4.0$ and an estimated $m^* ≈ 0.0156 m_e$. The transport data indicate surface conduction due to Fermi level pinning in the conduction band and a quasi-2D transport regime, supporting the suitability of InAsSb nanoflags for superconducting hybrids. Overall, the results position InAsSb nanoflags as a promising platform that combines high mobility, large g-factor, and surface states for topological superconductivity and related quantum devices.

Abstract

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.

Figures (4)

• Figure 1: (a) 45° tilted-view SEM image of InAsSb NFs under optimized growth conditions. Length marker $1$ µ m. Inset: top-view SEM image of the same sample, highlighting in yellow a NF with the desired morphology, in blue a much narrower and thicker NF that grows in the opposite direction. Length marker $200$ nm. (b) TEM micrograph of an isolated InAsSb NF. A single stacking fault originates at the stem-NF interface and propagates at the edge of the NF. Length marker $1$ µ m. (c) Sketch of a NF: in red the InAs stem, in blue the InAsSb NF, in green the stacking fault (SF).
• Figure 2: Four-probe longitudinal conductance $G_{xx}$ as a function of back-gate voltage $V_{bg}$, for two sweep directions, forward and backward, as indicated by the red arrows. In green, a linear fit to the forward-sweep curve in the [$-30$ V; $-20$ V] range, to obtain field-effect mobility. $T = 2.7$ K. Sweep rate: $0.086$ V/s.
• Figure 3: Hall effect measurements at two different temperatures, $2.7$ K and $0.44$ K. (a) Charge carrier density $n$ as a function of back-gate voltage $V_{bg}$. In the inset, the four-probe transverse voltage $V_{xy}$ is shown as a function of magnetic field $B$ at $0.44$ K for different back-gate voltages. The data has been corrected for the misalignment of the voltage probes in the longitudinal direction. (b) Hall mobility $\mu_H$ as a function of back-gate voltage.
• Figure 4: Colormap of the variation in longitudinal conductance $\partial G_{xx} / \partial V_{bg}$ with back-gate voltage, as a function of back-gate voltage $V_{bg}$ and magnetic field $B$. The relative minima of $G_{xx}$ along $V_{bg}$ for different values of $B$ are superimposed as white dots. Linear fits to subsets of the dots are represented in white for Landau levels with $N = 0,1,2$. The red continuous lines represent linear fits corresponding to the Zeeman-split Landau levels $N = 0$ and $N = 1$. On the right, a gray arrow indicates the Landau level splitting $\Delta E_{LL}$ at $B = 8$ T, while the red arrow indicates the Zeeman splitting $\Delta E_Z$ of the LLs, at the same magnetic field.