InSb Nanowires Research Articles

Uncovering bound states in the continuum in InSb nanowire networks

Bound states in the continuum (BICs) are exotic, localized states even though their energy lies in the continuum spectra. Since its discovery in 1929, the quest to unveil these exotic states in charge transport experiments remains an active pursuit in condensed matter physics. Here, we study charge transport in InSb nanowire networks in the ballistic regime and subject to a perpendicular magnetic field as ideal candidates to observe and control the appearance of BICs. We find that BICs reveal themselves as distinctive resonances or antiresonances in the conductance by varying the applied magnetic field and the Fermi energy. We systematically consider different lead connections in hashtag-like nanowire networks, finding the optimal configuration that enhances the features associated with the emergence of BICs. Finally, the investigation focuses on the effect of the Rashba spin–orbit interaction of InSb on the occurrence of BICs in nanowire networks. While the interaction generally plays a detrimental role in the signatures of the BICs in the conductance of the nanowire networks, it opens the possibility to operate these nanostructures as spin filters for spintronics. We believe that this work could pave the way for the unambiguous observation of BICs in charge transport experiments and for the development of advanced spintronic devices.

Atomic structure of In2O3 films on InSb nanowire and nanosheet

Surface reactions of indium antimonide (InSb) nanowires and nanosheets, including oxidation, often result in the performance deterioration of semiconductor devices. In this study, we characterized the oxide films of InSb nanowires/nanosheets at the atomic level. The oxide film on the nanowire is composed of In2O3, which grows in islands and layers along the (1¯11) and (002) planes of the matrix. The oxide film on the lateral side of the InSb nanosheet was amorphous and thinner than the oxide film on the nanowire. In2O3 grew via the external diffusion of indium ions. The oxide films on the InSb nanowires and nanosheets are closely related to the InSb surface features.

Stemless InSb nanowire networks and nanoflakes grown on InP

Among the experimental realization of fault-tolerant topological circuits are interconnecting nanowires with minimal disorder. Out-of-plane indium antimonide (InSb) nanowire networks formed by merging are potential candidates. Yet, their growth requires a foreign material stem usually made of InP–InAs. This stem imposes limitations, which include restricting the size of the nanowire network, inducing disorder through grain boundaries and impurity incorporation. Here, we omit the stem allowing for the growth of stemless InSb nanowire networks on an InP substrate. To enable the growth without the stem, we show that a preconditioning step using arsine (AsH3) is required before InSb growth. High-yield of stemless nanowire growth is achieved by patterning the substrate with a selective-area mask with nanohole cavities, containing restricted gold droplets from which nanowires originate. Interestingly, these nanowires are bent, posing challenges for the synthesis of interconnecting nanowire networks due to merging failure. We attribute this bending to the non-homogeneous incorporation of arsenic impurities in the InSb nanowires and the interposed lattice-mismatch. By tuning the growth parameters, we can mitigate the bending, yielding large and single crystalline InSb nanowire networks and nanoflakes. The improved size and crystal quality of these nanostructures broaden the potential of this technique for fabricating advanced quantum devices.

Thermal scanning probe and laser lithography for patterning nanowire based quantum devices

Semiconductor nanowire (NW) quantum devices offer a promising path for the pursuit and investigation of topologically-protected quantum states, and superconducting and spin-based qubits that can be controlled using electric fields. Theoretical investigations into the impact of disorder on the attainment of dependable topological states in semiconducting nanowires with large spin–orbit coupling and g-factor highlight the critical need for improvements in both growth processes and nanofabrication techniques. In this work, we used a hybrid lithography tool for both the high-resolution thermal scanning probe lithography and high-throughput direct laser writing of quantum devices based on thin InSb nanowires with contact spacing of 200 nm. Electrical characterization demonstrates quasi-ballistic transport. The methodology outlined in this study has the potential to reduce the impact of disorder caused by fabrication processes in quantum devices based on 1D semiconductors.

Influence of halogen precursors on the growth of InSb nanostructures

The present work highlights the role of halogen compounds in modifying the shape of the InSb nanostructures, while maintaining a high crystalline quality of the nanostructures. One-dimensional (1D) nanowires (NWs) and two-dimensional (2D) nanoplatelets (NPLs) were synthesized by ambient pressure chemical vapor deposition. Our experimental results suggest that at a critical growth temperature of 512 ∘C, InSb NWs grow by the traditional vapor–liquid–solid growth mechanism when gold (Au) nanoparticles are used to initiate growth on an InSb film. The resulting NWs were found to have a cylindrical or tapered shape, were of high crystalline quality, and had stoichiometric composition. In the presence of halogen precursors, a change in morphology was observed and the resulting nanostructures were 2D NPLs and faceted NWs. Using existing models of crystal growth and concepts of volume, surface and edge energies, the experimental results are explained on the basis of chlorine atoms adsorbed on the wide or narrow facets of a nanocrystal, initiating nucleation and facilitating NPL or faceted NW formation. The incorporation of the chlorine atoms add a new degree of freedom to CVD synthesis of nanostructures and the results are promising for the controlled growth of novel 1D and 2D nanostructures for nano-electronic devices.

Diffusive and ballistic transport in thin InSb nanowire devices using a few-layer-graphene-AlO x gate

Quantum devices based on InSb nanowires (NWs) are a prime candidate system for realizing and exploring topologically-protected quantum states and for electrically-controlled spin-based qubits. The influence of disorder on achieving reliable quantum transport regimes has been studied theoretically, highlighting the importance of optimizing both growth and nanofabrication. In this work, we consider both aspects. We developed InSb NW with thin diameters, as well as a novel gating approach, involving few-layer graphene and atomic layer deposition-grown AlO x . Low-temperature electronic transport measurements of these devices reveal conductance plateaus and Fabry–Pérot interference, evidencing phase-coherent transport in the regime of few quantum modes. The approaches developed in this work could help mitigate the role of material and fabrication-induced disorder in semiconductor-based quantum devices.

Spin-photon interaction in a nanowire quantum dot with asymmetrical confining potential

The electron (hole) spin–photon interaction is studied in an asymmetrical InSb (Ge) nanowire quantum dot. The spin–orbit coupling in the quantum dot mediates not only a transverse spin–photon interaction, but also a longitudinal spin–photon interaction due to the asymmetry of the confining potential. Both the transverse and the longitudinal spin–photon interactions have non-monotonic dependence on the spin–orbit coupling. For realistic spin–orbit coupling in the quantum dot, the longitudinal spin–photon interaction is much (at least one order) smaller than the transverse spin–photon interaction. The order of the transverse spin–photon interaction is about 1 nm in terms of length |zeg| , or 0.1 MHz in terms of frequency eE0|zeg|/h for a moderate cavity electric field strength E0=0.4 V m−1.

Magnetic properties of Mn-doped InSb nanowires from first principles

Room-temperature ferromagnetism (RTFM) has been achieved in Mn-doped InSb nanowires (NWs) through experiment. However, the underlying cause of RTFM remains unclear. In this paper, using first-principles calculations, the distribution of Mn ions and magnetic properties of Mn-doped wurtzite and zinc blend InSb NWs have been investigated. Our results indicate that wurtzite (In,Mn)Sb NWs can exhibit superior ferromagnetic behavior compared to zinc blend (In,Mn)Sb NWs. The distribution of Mn ions and magnetic properties in the (In,Mn)Sb NWs is influenced by their size, surface passivation and crystal structure. Furthermore, the ferromagnetic coupling is short-range in passivated (In,Mn)Sb NWs, and as the size of the NW decreases, the Mn-3d level becomes a deep acceptor in the band gap, resulting in an enhancement of ferromagnetism.

Spin-filtered measurements of Andreev bound states in semiconductor-superconductor nanowire devices

Semiconductor nanowires coupled to superconductors can host Andreev bound states with distinct spin and parity, including a spin-zero state with an even number of electrons and a spin-1/2 state with odd-parity. Considering the difference in spin of the even and odd states, spin-filtered measurements can reveal the underlying ground state. To directly measure the spin of single-electron excitations, we probe an Andreev bound state using a spin-polarized quantum dot that acts as a bipolar spin filter, in combination with a non-polarized tunnel junction in a three-terminal circuit. We observe a spin-polarized excitation spectrum of the Andreev bound state, which can be fully spin-polarized, despite strong spin-orbit interaction in the InSb nanowires. Decoupling the hybrid from the normal lead causes a current blockade, by trapping the Andreev bound state in an excited state. Spin-polarized spectroscopy of hybrid nanowire devices, as demonstrated here, is proposed as an experimental tool to support the observation of topological superconductivity.

Thermally tunable Dyakonov surface waves in semiconductor nanowire metamaterials

The development of engineered metamaterials has enabled the fabrication of tunable photonic devices capable of manipulating the characteristics of electromagnetic surface waves. Integration of semiconductors in metamaterials is a proven approach for creating thermally tunable metamaterials through temperature control of the semiconductor carrier density. In this paper, an interface consisting of an isotropic dielectric material as a cover and an indium antimonide (InSb) nanowire metamaterial as a substrate, is theoretically introduced to investigate the propagation conditions of Dyakonov surface waves in terahertz (THz) frequencies. Various temperature-dependent properties of Dyakonov surface waves in such a geometry is studied, including allowed THz regions, angular existence domain, dispersion relation, directionality, localization degree and figure of merit. The proposed configuration due to the presence of significant birefringence in InSb nanowire metamaterial, has potential applications in THz sensing, imaging and spectroscopy.

Growth evolution and polarization-dependent photoluminescence of lateral InSb/CdTe nanowires

The evolution of lateral InSb nanowires (NW) grown on CdTe (001) substrate by increasing of the InSb thickness is reported. At 10-nm growth of InSb, NW with narrow lateral width of ∼ 70 nm and high NW density (∼18 μm−1) are obtained. The evolutional description of InSb NW growth based on the atomic force microscopic characterization is presented. The intrinsic strain at the interface and top InSb layer is revealed by x-ray diffraction analysis. The strong polarization-dependent photoluminescence (PL) of NW is observed. The polarization degree of NW is ∼ 80% and 56% when the excited laser and the emission PL are polarized, respectively. The latter can be attributed to the shape anisotropy.

Epitaxially Driven Phase Selectivity of Sn in Hybrid Quantum Nanowires.

Hybrid semiconductor-superconductor nanowires constitute a pervasive platform for studying gate-tunable superconductivity and the emergence of topological behavior. Their low dimensionality and crystal structure flexibility facilitate unique heterostructure growth and efficient material optimization, crucial prerequisites for accurately constructing complex multicomponent quantum materials. Here, we present an extensive study of Sn growth on InSb, InAsSb, and InAs nanowires and demonstrate how the crystal structure of the nanowires drives the formation of either semimetallic α-Sn or superconducting β-Sn. For InAs nanowires, we observe phase-pure superconducting β-Sn shells. However, for InSb and InAsSb nanowires, an initial epitaxial α-Sn phase evolves into a polycrystalline shell of coexisting α and β phases, where the β/α volume ratio increases with Sn shell thickness. Whether these nanowires exhibit superconductivity or not critically relies on the β-Sn content. Therefore, this work provides key insights into Sn phases on a variety of semiconductors with consequences for the yield of superconducting hybrids suitable for generating topological systems.

Sulfur-Passivated InSb Nanowires for Infrared Photodetectors

Sulfur-passivated InSb nanowires (S-InSb NWs) with a single-crystalline structure were synthesized via a chemical vapor deposition process, where S plays the role of a growth catalyst as well as a surface passivator. Studies revealed that the prepared S-InSb NWs displayed typical n-type semiconductor behavior with a maximum field-effect mobility of 823.62 cm2 V–1 s–1 at room temperature. The S-InSb NW-based photodetector was characterized as possessing stable negative photoresponse properties toward incident infrared light, and the corresponding responsivity and external quantum efficiency were calculated to be 123.46 A/W and 14,400%, respectively, for 1.06 μm light and 120.99 A/W and 9680%, respectively, for 1.55 μm light. These values are higher than those for other reported photodetectors based on InSb nanosheets. Through the analysis of excited electron states in the band structure during light irradiation, the negative photoresponse was identified as stemming from the photogating effect of the Sb–S layer on the S-InSb NW surface. These outstanding transport and optoelectronic performances empower S-InSb NWs with technological potential to be used in next-generation infrared quantum devices.

Optically Tunable Transient Plasmons in InSb Nanowires.

Optical carrier incubation can effectively alter the electron transport properties of semiconductors; thus, optical switching of the plasmonic response of the semiconductor enables the ultrafast manipulation of the light at the nanoscale. Semiconductor nanostructures are promising platforms in on-chip high-speed plasmonic devices, owing to their high photoinduced electron injection efficiency at sub-picosecond and compatibility with contemporary semiconductor technologies. The pure single crystalline InSb nanowires are promising plasmonic materials in the mid-infrared region due to their high electron mobility and small electron effective mass. Here, the pump-probe nanoscopy is utilized to investigate the pump fluence dependency and the dynamics of the non-equilibrium plasmons in the InSb nanowires. The InSb plasmon is successfully switched by injecting the photoinduced electrons and the practical tuning of the plasmon frequency to one octave is shown by increasing the pump fluence from 0 to 90µJcm-2 . The density of the photoinduced electrons in InSb nanowires is 18.8×1018 cm-3 with pump fluence as low as 90µJcm-2 . The high electron mobility of the InSb supports the low-loss plasmon with a damping rate of ≈200cm-1 . The InSb nanowires' excellent plasmonic properties ensure that they are a promising platform for upcoming high-speed mid-infrared plasmonic materials for informatic devices.

Realization of a minimal Kitaev chain in coupled quantum dots.

Majorana bound states constitute one of the simplest examples of emergent non-Abelian excitations in condensed matter physics. A toy model proposed by Kitaev shows that such states can arise at the ends of a spinless p-wave superconducting chain1. Practical proposals for its realization2,3 require coupling neighbouring quantum dots (QDs) in a chain through both electron tunnelling and crossed Andreev reflection4. Although both processes have been observed in semiconducting nanowires and carbon nanotubes5-8, crossed-Andreev interaction was neither easily tunable nor strong enough to induce coherent hybridization of dot states. Here we demonstrate the simultaneous presence of all necessary ingredients for an artificial Kitaev chain: two spin-polarized QDs in an InSb nanowire strongly coupled by both elastic co-tunnelling (ECT) and crossed Andreev reflection (CAR). We fine-tune this system to a sweet spot where a pair of poor man's Majorana states is predicted to appear. At this sweet spot, the transport characteristics satisfy the theoretical predictions for such a system, including pairwise correlation, zero charge and stability against local perturbations. Although the simple system presented here can be scaled to simulate a full Kitaev chain with an emergent topological order, it can also be used imminently to explore relevant physics related to non-Abelian anyons.

Merging Nanowires and Formation Dynamics of Bottom‐Up Grown InSb Nanoflakes

AbstractIndium Antimonide (InSb) is a semiconductor material with unique properties, that are suitable for studying new quantum phenomena in hybrid semiconductor‐superconductor devices. The realization of such devices with defect‐free InSb thin films is challenging, since InSb has a large lattice mismatch with most common insulating substrates. Here, the controlled synthesis of free‐standing 2D InSb nanostructures, termed as “nanoflakes”, on a highly mismatched substrate is presented. The nanoflakes originate from the merging of pairs of InSb nanowires grown in V‐groove incisions, each from a slanted and opposing {111}B facet. The relative orientation of the two nanowires within a pair, governs the nanoflake morphologies, exhibiting three distinct ones related to different grain boundary arrangements: no boundary (type‐I), Σ3‐ (type‐II), and Σ9‐boundary (type‐III). Low‐temperature transport measurements indicate that type‐III nanoflakes are of a relatively lower quality compared to type‐I and type‐II, based on field‐effect mobility. Moreover, type‐III nanoflakes exhibit a conductance dip attributed to an energy barrier pertaining to the Σ9‐boundary. Type‐I and type‐II nanoflakes exhibit promising transport properties, suitable for quantum devices. This platform hosting nanoflakes next to nanowires and nanowire networks can be used to selectively deposit the superconductor by inter‐shadowing, yielding InSb‐superconductor hybrid devices with minimal post‐fabrication steps.

Tunable coupling between InSb nanowires and superconductors

The quest for topological states in hybrid nanowire devices has ignited substantial research in perfecting the nanowire-superconductor interface. Recent proposals, however, suggest that these immaculate interfaces can lead to an overly strong superconducting-semiconducting coupling that ``metalizes'' the nanowire (i.e., dominates its intrinsic properties which are essential for hosting topological particles). One way to reduce this coupling is to add an insulating shell between the nanowire and the superconductor. Here, we explore cadmium telluride (CdTe) shells as a tunnel barrier at the interface between indium antimonide (InSb) nanowires and a superconductor. We demonstrate the growth of epitaxial, defect-free CdTe on InSb and high-quality superconductor deposition at cryogenic temperatures, enabled by the near perfect lattice match of CdTe and InSb and their comparable thermal-expansion coefficients. Using growth and etching, we control the thickness of CdTe shells down to a few monolayers. This level of control indicates the potential of these shells to serve as a knob that modulates the coupling between a nanowire and a superconductor, possibly introducing a new generation of nanowire hybrids suitable for topological Majorana devices.

Surface band bending caused by native oxides on solution-processed twinned InSb nanowires with p-type conductivity.

Indium antimonide nanowires (InSb NWs) are attractive building-block candidates for bottom-up construction of high-efficiency electronics and optoelectronics due to their narrow direct band gap, fast room temperature carrier mobilities and small exciton binding energy. However, InSb NWs synthesized by the vapor-liquid-solution (VLS) mechanism generally suffer from an increased carrier and phonon scattering rate, which is thought to be caused by randomly distributed crystal defects along the NW growth direction. In this study, by utilizing the recently developed low-temperature, solution-processed technique, these crystal defects were successfully suppressed by periodically distributed twin planes to form twinned InSb nanowires. Importantly, measurements of the electrical transport properties of field effect transistors (FETs) reveal that the InSb NWs exhibit a hole-dominated conductivity with room temperature mobilities of up to 50.71 cm2 V-1 s-1, which is distinctly contrary to the intrinsic n-type InSb NWs. This observation of n-p switching behavior is probably attributed to the surface band bending effect with regard to the Fermi energy level, which is caused by surface oxide trap states arising from the native-oxide layer at the surface of the InSb NWs. All these results illustrate that the as-prepared colloidal InSb NWs can potentially be used as p-type materials for integration with next-generation nanoscale electronics and optoelectronics via surface engineering.

Magnetic field constraint for Majorana zero modes in a hybrid nanowire

The hybrid semiconductor-superconductor nanowire is expected to serve as an experimental platform to support Majorana zero modes. By rederiving its effective Kitaev model with spins, we discover a topological phase diagram, which assigns a more precise constraint on the magnetic field strength for the emergence of Majorana zero modes. We find that the effective pairing strength dressed by the proximity effect exhibits a significant dependence on the magnetic field, and thus the topological phase region is refined into a closed triangle in the phase diagram with chemical potential vs Zeeman energy (which is obviously different from the open hyperbolic region known before). This prediction is confirmed again by an exact calculation of quantum transport, where the zero bias peak of $2{e}^{2}/h$ in the differential conductance spectrum, as the necessary evidence for the Majorana zero modes, disappears when the magnetic field grows too strong. Therefore, the hybrid nanowire system does not support Majorana zero modes under a too strong magnetic field. For illustrations with practical hybrid systems, in the InSb nanowire coupled to NbTiN, the accessible magnetic field range is around 0.1--1.5 T; when coupled to an aluminum shell, the accessible magnetic field range should be smaller than 0.12 T. Our predictions are essential to significantly narrow down the range of magnetic fields for further searching Majorana zero modes in experiments.

Direct growth of InSb nanowires on CdTe (0 0 1) substrates by molecular beam epitaxy

The molecular beam epitaxial growth of InSb on CdTe (001) substrates has been performed with a specific growth condition, that results in elongated wire morphology. Atomic force microscopy (AFM) and field emission scanning electron microscopy are performed for characterizing the surface morphology. The AFM images of free-standing InSb/CdTe samples reveal the InSb nanowires (NWs) elongation along the [110] direction of the substrate. We speculate the growth mechanism of NWs by attempting to investigate the intrinsic strain by X-ray diffraction (XRD) analysis. The XRD reveals the compressive strain in InSb epilayer and it could be the origin of NW formation. Phonon scatterings from CdTe, InSb and intermixed compounds are probed by Raman spectroscopy. Optical properties of the lateral NWs on CdTe are revealed by photoluminescence measurements.