Growth and Transport Properties of InAsSb Nanoflags

The gist: The present work reports, for the first time, the growth of high-quality free-standing InAsSb nanoflags and their electronic properties.

Material Properties and Growth

Different growth conditions have been explored, and zinc-blende InAsSb nanoflags of various composition have been obtained 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. The estimated Landé g-factor of these InAsSb NFs is g∗ = 58.7 ± 4.0, which is in good agreement with the recently reported value of g∗ ∼ 55 for an InAsSb shallow QW.

Experimental Synthesis and Characterization

The synthesis of the InAs-InAsSb heterostructures has been carried out by Au-assisted vapor-liquid-solid (VLS) growth in a chemical beam epitaxy (CBE) system on InAs(111)B substrates. The morphology of the grown samples has been studied through field-emission scanning electron microscopy (SEM), employing a Zeiss Merlin SEM with an accelerating voltage of 5 kV and probe current between 90 pA and 100 pA, detecting secondary electrons. To characterize the heterostructure crystal structure and chemical composition, the InAsSb NFs have been mechanically transferred on a Cu grid and studied by transmission electron microscopy (TEM) in a JEOL JEM-F200 operated at 200 kV, equipped with an EDX spectrometer.

Electronic Transport Measurements

Low temperature transport measurements have been performed at 2.7 K, at B = 0, B = 0.25 T, and B = −0.25 T. The data was measured with an AC current bias of 100 nA and performing back-gate voltage sweeps, back and forth, between ±40 V. From the measurements at B = 0, we calculated the longitudinal conductance Gxx as follows: Gxx = Rxx / (R2xx + R2xy) ≈ 1/Rxx. The field-effect mobility obtained from the linear fit to the conductance curve is µFE = LWCox · ∂Gxx / ∂Vbg. We found the oxide capacitance to be Cox = εSiO2 / ε0 tox, and this value is in good agreement with previous work. The field-effect mobility obtained from the linear fit to the conductance curve is µFE = 2.2 · 104 cm 2/(Vs) (at 2.7 K).

Magneto-transport Analysis

Hall effect measurements were taken, for different Vbg values, by measuring source-drain current Isd, longitudinal four-probe voltage drop Vxx, and Hall voltage Vxy with lock-in amplifiers with an AC current bias of 100 nA. The charge carrier density n is calculated as n = Isd / e · ∂Vxy / ∂B −1. The Hall mobility is calculated as µH = L W · ⟨Vxx⟩ · ∂Vxy / ∂B. At 0.44 K, Hall mobility has a peak of about 2.6 · 104 cm 2/(Vs) (at a corresponding carrier density n ≈ 4·1012 cm−2), which is in line with Hall mobilities reported in previous studies for InSb nanoflags, InSb shallow quantum wells, and InAsSb shallow QWs.

Conclusion and Outlook

An advantage of the InAsSb material system compared to InAs and InSb is the larger Landé g-factor while maintaining a comparable mobility. Ternary compounds are generally more challenging to grow than binaries, but on the other hand, they allow control on lattice constant, band gap, and effective mass via composition engineering. Compared to one-dimensional nanowires, two-dimensional systems allow greater flexibility in device design and fabrication. Finally, compared to NFs, quantum wells constitute a scalable technology that can provide high mobility but their active region is typically buried more than 100 nm under the surface. The InAsSb NFs have a large Landé g-factor of 58.7 ± 4.0 and show signs of surface conduction. These characteristics make them a promising platform to study topological superconductivity in hybrid S-Sm systems and a good candidate to host exotic bound states.

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JournalName

Growth and Transport Properties of InAsSb Nanoflags†

Sebastian Serra,a Gaurav Shukla,a Giada Bucci,a Robert Sorodoc,a Valentina Zannier,a Fabio Beltram,a Lucia Sorba,a and Stefan Heuna

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.

1 Introduction

III-V semiconductors have been the subject of extensive study, as they are considered ideal for a variety of electronic and optoelectronic applications, like high-performance transistors, 1–3 light emitters, 4,5 photodetectors, 6,7 and photovoltaics. 8,9 In particular, high quality crystals with narrow band gap, strong spinorbit interaction, and large Landé g-factor are considered promising platforms for optoelectronics, spintronics, and quantum computing applications. Among these compounds, indium arsenide (InAs), indium antimonide (InSb), and the ternary alloy indiumarsenide-antimonide (InAsSb), represent ideal candidates for these purposes.

InAs has a narrow and direct bandgap (∼ 0.39 eV in wurtzite structure and ∼ 0.35 eV in zincblende structure, at a temperature of 300 K), 10 low effective mass (m∗ InAs = 0.023me, where me is the rest mass of the free electron), 11 high carrier mobility (> 106 cm2/(Vs) in 2DEGs in InAs quantum wells, 12,13 and (6500 − 8000 cm2/(Vs) in nanoflags (NFs)), and a relatively large Landé g-factor (g∗ = 17.0±0.5 in InAs 2DEGs, 15 larger than for InAs bulk, where g∗ bulk = 14.7. Due to these properties, extensive studies have been conducted on InAs 1D and 2D nanostructures. Moreover, due to the strong spin-orbit interaction, InAs 2DEGs have been proposed as a platform for topological superconductivity in hybrid superconductor-semiconductor (S-Sm) systems.

InSb has an even narrower direct bandgap of 0.17 eV and a lower effective mass than InAs (m∗ InSb = 0.014me), 11,22 high carrier mobility (up to 3.5 · 105 cm2/(Vs) in quantum wells,, one order of magnitude less in free-standing nanostructures),, large Landé g-factor (∼ 50), and even stronger Rashba spinorbit strength than InAs. For these reasons, this material has recently been considered as a promising platform for topological applications in S-Sm systems, and gate controlled supercurrents are under study in InSb-based Josephson junctions,.

1. The improved AI system can accurately predict Landé g-factors by using Eq. 9 derived from experimental measurements: g∗ = 2 m∗/me ∆EZ / ∆ELL. This allows for reliable prediction of material properties based on measured effective masses and magnetic field parameters, specifically estimating the Landé g-factor of InAs0.77Sb0.23 NFs to be 58.7±4.0.

2. The AI system can model charge carrier density and Hall mobility under various conditions by utilizing the derived formulas: n = Isd / e · ∂Vxy / ∂B −1 and µH = L W · ⟨Vxx⟩ · ∂Vxy / ∂B. This capability enables the prediction of transport properties as a function of back-gate voltage and magnetic field, including identifying regimes where Hall mobility peaks, such as the peak Hall mobility at 0.44 K has a peak of about 2.6 · 104 cm2/(Vs).

3. The system can predict Landau level filling factors based on the measured slopes in the conductance variation using kN = e απħ / (N + 1/2). This allows for the identification of spin-degenerate Landau levels by analyzing the experimentally observed ratios k1/k0 = 3 and k2/k1 = 5/3, which is crucial for understanding magneto-transport effects.

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.