InAs Nanowires Research Articles

Destructive Little-Parks Effect in a Full-Shell Nanowire-Based Transmon.

A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low E_{J}/E_{C} regime. Little-Parks oscillations as a function of flux along the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction is not resolved beyond line broadening, placing a bound on Majorana coupling, E_{M}/h<10 MHz, much smaller than the Josephson coupling E_{J}/h∼4.7 GHz.

Evidence of half-integer Shapiro steps originated from nonsinusoidal current phase relation in a short ballistic InAs nanowire Josephson junction

We report on half-integer Shapiro steps observed in an InAs nanowire Josephson junction. We observed the Shapiro steps of the short ballistic InAs nanowire Josephson junction and found anomalous half-integer steps in addition to the conventional integer steps. The half-integer steps disappear as the temperature increases or transmission of the junction decreases. These experimental results agree closely with numerical calculation of the Shapiro response for the skewed current phase relation in a short ballistic Josephson junction.

Long interior carrier lifetime in selective-area InAs nanowires on silicon

Catalyst-free, position-controlled indium arsenide (InAs) nanowires (NWs) of variable diameters were grown on Si (111) by selective-area epitaxy (SAE). Ultrafast pump-probe spectroscopy was conducted, from which carrier recombination mechanisms on the NW surface and interior were resolved and characterized. NWs grown using SAE demonstrated high optical quality, showing minority carrier lifetimes more than two-fold longer than that of the randomly-positioned (RP) NWs. The extracted SAE-InAs NW interior recombination lifetime was found to be as long as 7.2 ns, 13X longer than previous measurements on RP-NWs; and the surface recombination velocity 4154 cm · s- 1. Transmission electron microscopy revealed a high density of stacking defects within the NWs, suggesting that interior recombination lifetime can be further increased by improving NW interior crystalline quality.

Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires

We report transport measurements and tunneling spectroscopy in hybrid nanowires with epitaxial layers of superconducting Al and the ferromagnetic insulator EuS, grown on semiconducting InAs nanowires. In devices where the Al and EuS covered facets overlap, we infer a remanent effective Zeeman field of order 1 T, and observe stable zero-bias conductance peaks in tunneling spectroscopy into the end of the nanowire, consistent with topological superconductivity at zero applied field. Hysteretic features in critical current and tunneling spectra as a function of applied magnetic field support this picture. Nanowires with non-overlapping Al and EuS covered facets do not show comparable features. Topological superconductivity in zero applied field allows new device geometries and types of control.

Integration of Indium Arsenide/Indium Phosphide Core-Shell Nanowire Vertical Gate-All-Around Field-Effect Transistors on Si

Among the III-V semiconductor materials, indium arsenide (InAs) nanowire (NWs) with high carrier mobility are expected to be alternative channels for high-performance and low-power field-effect transistors (FETs). However, there is a challenge in enhancing the on-state current for the InAs NW-channel vertical gate-all-around (VGAA) structures on Si. We investigated vertical InAs/InP core-shell (CS) NW-channels to enhance the current and demonstrated InAs/InP CS NW VGAA FETs. The InAs/InP CS NW-channel enhanced the on-state current while maintaining a small off-leakage current. The devices showed an on-state current of 40 $\mu \text{A}/\mu \text{m}$ , off-leakage current of 1 pA/ $\mu \text{m}$ , and subthreshold slope of 111 mV/dec at $\text{V}_{\text {DS}} =0.50$ V. The origin of the current enhancement suggests that there is a formation of two-dimensional electron gas (2DEG) in the InAs/InP CS NW-channel, and the characteristics of the InAs/InP CS NW VGAA FET revealed that the InP interlayer at draian edge and low source resistivity are important parameters to take advantage of 2DEG for CS NW VGAA FET.

Improved microwave sensitivity to 706 kV/W by using p-GaAsSb/n-InAs nanowire backward diodes for low-power energy harvesting at zero bias

In this study, a p-GaAs0.4Sb0.6/n-InAs nanowire backward diode (NW BWD) with a large sensitivity of 706 kV/W, exceeding that of Schottky barrier diodes (SBDs), was developed for low-power microwave rectification at zero bias. The interband tunneling of the NW BWDs under zero-bias condition displayed a large nonlinear characteristic of typical BWDs, which is effective for realizing power detection with high sensitivity. The fabricated NW BWDs indicated linear detected voltages (Vdet) when a microwave input power (Pin) of ∼1 µW was applied at 2.4 GHz. From the Vdet, Pin, and return loss obtained from the S-parameter measurements, an impedance-matched voltage sensitivity of 706 kV/W was calculated for the NW BWD at zero bias. The obtained sensitivity value was higher than that of a well-designed SBD, which was ∼62 kV/W at 2.4 GHz. According to the extracted device parameters, it was found that to improve the sensitivity of the NW-BWD, not only the junction capacitance of the diode but also the parasitic pad capacitance needs to be reduced. The high sensitivity is attributed to the high curvature coefficient of −26.7 V−1 and the small junction capacitance of the NW structure of the BWD.

Surface-States-Modulated High-Performance InAs Nanowire Phototransistor.

We report a high-performance InAs nanowire phototransistor with the photoresponse mechanism governed by the gate-controlled surface states. Detailed characterizations suggest that the high density of surface defect states of the InAs nanowire can capture electrons from the nanowire core to form negative surface charge centers. Before and after light illumination, nanowire surface states undergo processes of capturing and neutralizing the electrons, respectively. This leads to an increase in the concentration and mobility of electrons after light illumination, which endows the device with remarkable photoresponsivity. After modulating the surface states through gate voltage and surface passivation, significantly high responsivity of up to 4.4 × 103 A/W and gain of up to 2.7 × 103 under the illumination of light at the wavelength of 2000 nm are obtained, putting our devices among the high-performance short-wave infrared nanowire photodetectors. This work provides an important reference for understanding the surface effects of nanomaterials and enhancing the performance of nanophotodetectors by modulating the surface states.

Hot-carrier separation in heterostructure nanowires observed by electron-beam induced current

The separation of hot carriers in semiconductors is of interest for applications such as thermovoltaic photodetection and third-generation photovoltaics. Semiconductor nanowires offer several potential advantages for effective hot-carrier separation such as: a high degree of control and flexibility in heterostructure-based band engineering, increased hot-carrier temperatures compared to bulk, and a geometry well suited for local control of light absorption. Indeed, InAs nanowires with a short InP energy barrier have been observed to produce electric power under global illumination, with an open-circuit voltage exceeding the Shockley-Queisser limit. To understand this behaviour in more detail, it is necessary to establish control over the precise location of electron-hole pair-generation in the nanowire. In this work we perform electron-beam induced current measurements with high spatial resolution, and demonstrate the role of the InP barrier in extracting energetic electrons.We interprete the results in terms of hot-carrier separation, and extract estimates of the hot carriers’ mean free path.

1D semiconductor nanowires for energy conversion, harvesting and storage applications

Abstract The accomplishment of 1D semiconductor nanowires (SN) in the field of energy has attracted intense interest in recent years due to their advantageous properties (e.g., large surface area, unique surface chemistry, and tunable transport properties). Considerable efforts were devoted to explore 1D-SN building blocks as the harvesting channel/unit (e.g., in thermal, chemical, mechanical, and solar energy applications) and as the storage media (for electrochemical energy). A wide bandgap tuning of SN in the range of 0.39 eV (in case of InAs nanowires) to 4.66 eV (in case of β-Ga2O3 nanowires) due to quantum size effect makes them a suitable candidate for optoelectronic applications. This review focuses on 1D-SN wherein the travel of electron and photon is confined in two directions but in one dimension. The SN emerged as promising nanostructures for developing electronic devices of high carrier-mobilities (e.g., >12000 cm2V−1s−1 for holes and 3000 cm2V−1s−1 for electrons in case of Ge nanowires). A list of efficient fabrication strategies (e.g., vapor-liquid-solid [VLS], hard-template approaches, and solution-phase) are discussed along with ultrafast electron transport dynamics of SN and piezoelectric nanowires. The control on electrons, photons, and phonons transport makes 1D-SN ideal for solid-state energy conversion, harvesting, and storage applications. State-of-the-art 1D-SN energy nano-systems have been demonstrated to yield diverse outcomes of high significance including single-nanowire and array-based photovoltaic cells (InP nanowires with a maximum power conversion efficiency up to 17.8%), nanogenerators (SiGe nanowires with a maximum power output of 7.1 μW/cm2), supercapacitors (core-shell hierarchical CoS@MoS2 nanowire array with an energy density of 95.7 Wh kg−1 at power density of 711.2 W kg−1), and lithium-air batteries (3D freestanding hierarchical CuCo2O4 nanowires@Ni foam with an excellent specific capacity of 13654 mAh g−1 at 0.1 mA cm−2). This review will serve as a key platform to understand 1D-SN to fabricate the next-generation novel nano-systems for developing efficient energy devices of high performance.

Strategy for accurate thermal biasing at the nanoscale

We analyze the benefits and shortcomings of a thermal control in nanoscale electronic conductors by means of the contact heating scheme. Ideally, this straightforward approach allows one to apply a known thermal bias across nanostructures directly through metallic leads, avoiding conventional substrate intermediation. We show, by using the average noise thermometry and local noise sensing technique in InAs nanowire–based devices, that a nanoscale metallic constriction on a SiO2 substrate acts like a diffusive conductor with negligible electron-phonon relaxation and non-ideal leads. The non-universal impact of the leads on the achieved thermal bias—which depends on their dimensions, shape and material composition—is hard to minimize, but is possible to accurately calibrate in a properly designed nano-device. Our results allow to reduce the issue of the thermal bias calibration to the knowledge of the heater resistance and pave the way for accurate thermoelectric or similar measurements at the nanoscale.

A comparative study of graphite and silicon as suitable substrates for the self-catalysed growth of InAs nanowires by MBE

In order to fully exploit the enormous potential of functional monolithic nanowire/graphene hybrid structures in high-performance flexible devices, a better understanding of the influence of the graphitic substrate (GS) on NWs growth is crucial. InAs nanowires (NWs) were simultaneously grown on Si and GS with identical growth temperature, In-flux and V/III flux ratio via an In-catalysed growth technique. It is demonstrated that the GS is a more favourable platform for the growth of dense InAs NWs under highly In-rich conditions (low V/III flux ratio), whereas silicon is a more suitable substrate under a highly As-rich condition (high V/III flux ratio). It is shown that the GS enables NWs growth at high In-flux which has enormous potential for the fabrication of cost-effective nanodevices. Transmission electron microscopy analysis of the NW/GS interface confirms the NWs are well aligned on the graphitic substrate. This study opens new possibilities for the choice of suitable substrate for the optimal growth of NWs under various conditions.

Imaging the Thermalization of Hot Carriers After Thermionic Emission Over a Polytype Barrier

The thermalization of non-equilibrium charge carriers is at the heart of thermoelectric energy conversion. In nanoscale systems, the equilibration length can be on the order of the system size, leading to a situation where thermoelectric effects need to be considered as spatially distributed, rather than localized at junctions. The energy exchange between charge carriers and phonons is of fundamental scientific and technological interest, but their assessment poses significant experimental challenges. We addressed these challenges by imaging the temperature change induced by Peltier effects in crystal phase engineered InAs nanowire (NW) devices. Using high-resolution scanning thermal microscopy (SThM), we have studied current-carrying InAs NWs, which feature a barrier segment of wurtzite (WZ) of varying length in a NW of otherwise zincblende (ZB) crystal phase. The energy barrier acts as a filter for electron transport around the Fermi energy, giving rise to a thermoelectric effect. We find that thermalization through electron-phonon heat exchange extends over the entire device. We analyze the temperature profile along a nanowire by comparing it to spatially dependent heat diffusion and electron thermalization models. We are able to extract the governing properties of the system, including the electron thermalization length of $223 \pm 9$\,nm, Peltier coefficient and Seebeck coefficient introduced by the barrier of $39 \pm 7$\,mV and $89 \pm 21$\,$\mu$V/K, respectively, and a thermal conductivity along the wire axis of $8.9 \pm 0.5$\,W/m/K. Finally, we compare two ways to extract the elusive thermal boundary conductance between NW and underlying substrate.

Recent progress on infrared photodetectors based on InAs and InAsSb nanowires

In recent years, quasi-1D semiconductor nanowires have attracted significant research interest in the field of optoelectronic devices. Indium arsenide (InAs) nanowire, a III–V compound semiconductor structure with a narrow band gap, shows high electron mobility and high absorption from the visible to the mid-wave infrared (MWIR), holding promise for room-temperature high-performance infrared photodetectors. Therefore, the material growth, device preparation and performance characteristics have attracted increasing attention, enabling high-sensitivity InAs nanowire photodetector from the visible to the MWIR at room temperature. This review starts by discussing the growth process of the low-dimensional structure and elementary properties of the material, such as the crystalline phase, mobility, morphology, surface states and metal contacts. Then, three solutions, including the visible-light-assisted infrared photodetection technology, vertical nanowire-array technology and band engineering by the growth of InAsSb nanowires with increasing Sb components, are elaborated to obtain longer cut-off wavelength MWIR photodetectors based on single InAs nanowire and its heterojunction structure. Finally, the potential and challenges of the state-of-the-art optoelectronic technologies for InAs nanowire MWIR photodetectors are summarized and compared, and preliminary suggestions for the technical development route and prospects are presented. This review mainly delineates the research progress of material growth, device fabrication and performance characterization of InAs nanowire MWIR photodetectors, providing a reference for the development of the next-generation high-performance photodetectors over a wide spectrum range.

A theoretical and experimental study on effect of growth time on self-catalyzed InAs nanowires

We in detail investigated the effect of growth time on InAs nanowires (NWs) grown on Si substrates by metal-organic chemical vapor deposition. It is found that the axial growth of InAs NWs is nonlinear and shows different trends with different NW diameters. Thin NWs grow faster than thick NWs in length, and the radius of both thin and thick NWs have no dependence on growth time. Based on self-catalyzed growth mechanism, we established a kinetic growth process to simulate the growth of InAs NWs on Si. We analyzed some dependences, including length-time, diameter-time and length-diameter dependences. Calculations are in good agreements with experimental ones. It indicates that growth saturation and growth rates of NWs are determined by diffusion length of In adatoms, initial diameter of seed particles and the amount of adatoms per unit area.

Electrical transport properties of InAs nanowires synthesized by a solvothermal method

Nanowires are widely considered to be key elements in future disruptive electronics and photonics. This paper presents the first detailed study of transport mechanisms in single-crystalline InAs nanowires synthesized by a cheap solvothermal wet chemical method. From detailed analyses of temperature-dependent current–voltage characteristics, it was observed that contacted nanowires operate in a linear transport regime at biases below a critical cross-over voltage. For larger biases, the transport changes to space-charge-limited conduction assisted by traps. The characteristic parameters such as free electron concentration, trap concentration and energy distribution, and electron mobility were all calculated. It was demonstrated that the nanowires have key electrical properties comparable to those of InAs nanowires grown by molecular beam epitaxy. Our results might pave the way for cheap disruptive low-dimensional electronics such as resistive switching devices.

Anomalous Coulomb Drag between InAs Nanowire and Graphene Heterostructures.

Correlated charge inhomogeneity breaks the electron-hole symmetry in two-dimensional (2D) bilayer heterostructures which is responsible for nonzero drag appearing at the charge neutrality point. Here we report Coulomb drag in novel drag systems consisting of a two-dimensional graphene and a one-dimensional (1D) InAs nanowire (NW) heterostructure exhibiting distinct results from 2D-2D heterostructures. For monolayer graphene (MLG)-NW heterostructures, we observe an unconventional drag resistance peak near the Dirac point due to the correlated interlayer charge puddles. The drag signal decreases monotonically with temperature (∼T^{-2}) and with the carrier density of NW (∼n_{N}^{-4}), but increases rapidly with magnetic field (∼B^{2}). These anomalous responses, together with the mismatched thermal conductivities of graphene and NWs, establish the energy drag as the responsible mechanism of Coulomb drag in MLG-NW devices. In contrast, for bilayer graphene (BLG)-NW devices the drag resistance reverses sign across the Dirac point and the magnitude of the drag signal decreases with the carrier density of the NW (∼n_{N}^{-1.5}), consistent with the momentum drag but remains almost constant with magnetic field and temperature. This deviation from the expected T^{2} arises due to the shift of the drag maximum on graphene carrier density. We also show that the Onsager reciprocity relation is observed for the BLG-NW devices but not for the MLG-NW devices. These Coulomb drag measurements in dimensionally mismatched (2D-1D) systems, hitherto not reported, will pave the future realization of correlated condensate states in novel systems.

Pulsed THz emission from wurtzite phase catalyst-free InAs nanowires

The wurtzite phase catalyst-free InAs nanowires were investigated under femtosecond laser pulse photoexcitations. It was found that the THz radiation emission mechanisms depend on an exciting laser beam polarization, namely, the plasma oscillations for perpendicular to nanowire optical electric fields, and the ballistically moving carrier separation for the parallel polarization fields. The energetic distance between Γ7c and Γ8c conduction bands was experimentally determined to be 0.5 eV.

Anomalous metallic phase in tunable destructive superconductors

Multiply connected superconductors smaller than the coherence length show destructive superconductivity, characterized by reentrant quantum phase transitions driven by magnetic flux. We investigate the dependence of destructive superconductivity on flux, transverse magnetic field, temperature, and current in InAs nanowires with a surrounding epitaxial Al shell, finding excellent agreement with mean-field theory across multiple reentrant transitions. Near the crossover between destructive and nondestructive regimes, an anomalous metal phase is observed with temperature-independent resistance, controlled over two orders of magnitude by a millitesla-scale transverse magnetic field.

Temperature-dependence calculation of lattice thermal conductivity and related parameters for the zinc blende and wurtzite structures of InAs nanowires

Theoretical calculations are performed on lattice thermal conductivity (LTC) and related parameters for the zinc blende and wurtzite structure of InAs nanowires (NWs) with diameters of 50, 63, 66, 100 and 148 nm through the Morelli–Callaway model. For the model to be efficiently applicable, the longitudinal and transverse modes are considered. The melting point of the various-sized NWs is considered to estimate the Debye and phonon group velocities. The impacts of Gruneisen parameter, dislocations and surface roughness are also successfully utilized to address the calculated and measured LTC of the semiconductor under investigation. Results show that the Gruneisen parameter increases with decreasing NW diameter and that phonon confinement leads to an observable deviation of the calculated LTC curve from that of the experimental one in the case of bulk InAs. We assume that NW boundaries, dislocations and imperfections are responsible for the scattering of phonons along with electrons and other phonons because of normal and Umklapp processes. Therefore, at a specified temperature, LTC depends on the size and crystal structure of the semiconductor. As such, the thermal and mechanical parameters of InAs can be greatly modified by decreasing the size and dimension of the semiconductor as a result of the quantum-confinement effect.

Highly symmetric and tunable tunnel couplings in InAs/InP nanowire heterostructure quantum dots

We present a comprehensive electrical characterization of an InAs/InP nanowire (NW) heterostructure, comprising of two InP barriers forming a quantum dot (QD), two adjacent lead segments and two metallic contacts. We demonstrate how to extract valuable quantitative information of the QD. The QD shows very regular Coulomb blockade resonances over a large gate voltage range. By analyzing the resonance line shapes, we map the evolution of the tunnel couplings from the few to the many electron regime, with electrically tunable tunnel couplings from <1 μeV to >600 μeV, and a transition from the temperature to the lifetime broadened regime. The InP segments form tunnel barriers with almost fully symmetric tunnel couplings and a barrier height of ∼350 meV. All of these findings can be understood in great detail based on the deterministic material composition and geometry. Our results demonstrate that integrated InAs/InP QDs provide a promising platform for electron tunneling spectroscopy in InAs NWs, which can readily be contacted by a variety of superconducting materials to investigate subgap states in proximitized NW regions, or be used to characterize thermoelectric nanoscale devices in the quantum regime.