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In the emerging interdisciplinary field of iontronics, ionic motion and arrangement in electrolyte media are exploited to control the properties and functionalities of electronic devices. This approach encompasses a wide range of applications across engineering and physical sciences including solid-state physics, electronics and energy storage. We briefly discuss the use of approaches and techniques characteristic of iontronics in nanoscale devices based on III-V semiconductor nanostructures, a versatile and promising platform for nanoscience and nanotechnology applications. Then, we report and discuss the operation of InAs nanowire-based electrolyte-gated transistors implemented using ionic liquids. We show that the ionic liquid gating outperforms the conventional solid-state back gate, and we compare the current modulation achieved in the same InAs NW using the ionic liquid gate or the back-gate. Finally, we highlight the capability of the liquid electrolyte to drastically change the resistance dependence on temperature in the nanowire. Our results suggest promising strategies toward the advanced field effect control of innovative III-V semiconductor nanowire-based devices for information and communication technologies at large.In the emerging interdisciplinary field of iontronics, ionic motion and arrangement in electrolyte media are exploited to control the properties and functionalities of electronic devices. This approach encompasses a wide range of applications across engineering and physical sciences including solid-state physics, electronics and energy storage. We briefly discuss the use of approaches and techniques characteristic of iontronics in nanoscale devices based on III-V semiconductor nanostructures, a versatile and promising platform for nanoscience and nanotechnology applications. Then, we report and discuss the operation of InAs nanowire-based electrolyte-gated transistors implemented using ionic liquids. We show that the ionic liquid gating outperforms the conventional solid-state back gate, and we compare the current modulation achieved in the same InAs NW using the ionic liquid gate or the back-gate. Finally, we highlight the capability of the liquid electrolyte to drastically change the resistance dependen...

We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis that allows to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of Josephson junctions based on High-Temperature Superconductors is discussed., Comment: 8 pages, 5 figures

We fabricate dual-gated electric double layer (EDL) field effect transistors based on InAs nanowires gated with an ionic liquid, and we perform electrical transport measurements in the temperature range from room temperature to 4.2 K. By adjusting the spatial distribution of ions inside the ionic liquid employed as gate dielectric, we electrostatically induce doping in the nanostructures under analysis. We extract low-temperature carrier concentration and mobility in very different doping regimes from the analysis of current-voltage characteristics and transconductances measured exploiting global back-gating. In the liquid gate voltage interval from -2 to 2 V, carrier concentration can be enhanced up to two orders of magnitude. Meanwhile, the effect of the ionic accumulation on the nanowire surface turns out to be detrimental to the electron mobility of the semiconductor nanostructure: The electron mobility is quenched irrespectively to the sign of the accumulated ionic species. The reported results shine light on the effective impact on crucial transport parameters of EDL gating in semiconductor nanodevices and they should be considered when designing experiments in which electrostatic doping of semiconductor nanostructures via electrolyte gating is involved. We fabricate dual-gated electric double layer (EDL) field effect transistors based on InAs nanowires gated with an ionic liquid, and we perform electrical transport measurements in the temperature range from room temperature to 4.2 K. By adjusting the spatial distribution of ions inside the ionic liquid employed as gate dielectric, we electrostatically induce doping in the nanostructures under analysis. We extract low-temperature carrier concentration and mobility in very different doping regimes from the analysis of current-voltage characteristics and transconductances measured exploiting global back-gating. In the liquid gate voltage interval from -2 to 2 V, carrier concentration can be enhanced up to two orders of magnitude. Meanwhile, the effect of the ionic accumulation on the nanowire surface turns out to be detrimental to the electron mobility of the semiconductor nanostructure: The electron mobility is quenched irrespectively to the sign of the accumulated ionic species. The reported results shine light on the effective impact on crucial transport parameters of EDL gating in semiconductor nanodevices and they should be considered when designing experiments in which electrostatic doping of semiconductor nanostructures via electrolyte gating is involved.

Research interest in indium antimonide (InSb) has increased significantly in recent years owing to its intrinsic properties and the consequent opportunities to implement next-generation quantum devices. Hence, the precise, reproducible control over morphology and crystalline quality becomes of paramount importance for a practical quantum-device technology. Here, we investigate the growth of InSb nanostructures with different morphologies on InAs stems without pre-growth efforts (patterning). InSb nanostructures such as nanowires (1D), nanoflags (2D) and nanocubes (3D) have been realized by means of Au-assisted chemical beam epitaxy by tailoring the growth parameters like growth temperature, precursor fluxes, sample rotation and substrate orientation. Through morphological and crystallographic characterization, all the as-grown InSb 2D nanostructures are found to be single-crystalline with zinc blende structure, free from any defects such as stacking faults and twin planes. The existence of two families of 2D nanostructures, characterised by an aperture angle at the base of 145 and 160 , is observed and modelled. This study provides useful guidelines for the controlled growth of high-quality InSb nanostructures with different shape. Research interest in indium antimonide (InSb) has increased significantly in recent years owing to its intrinsic properties and the consequent opportunities to implement next-generation quantum devices. Hence, the precise, reproducible control over morphology and crystalline quality becomes of paramount importance for a practical quantum-device technology. Here, we investigate the growth of InSb nanostructures with different morphologies on InAs stems without pre-growth efforts (patterning). InSb nanostructures such as nanowires (1D), nanoflags (2D) and nanocubes (3D) have been realized by means of Au-assisted chemical beam epitaxy by tailoring the growth parameters like growth temperature, precursor fluxes, sample rotation and substrate orientation. Through morphological and crystallographic characterization, all the as-grown InSb 2D nanostructures are found to be single-crystalline with zinc blende structure, free from any defects such as stacking faults and twin planes. The existence of two families of 2D nanostructures, characterised by an aperture angle at the base of 145 and 160 , is observed and modelled. This study provides useful guidelines for the controlled growth of high-quality InSb nanostructures with different shape.

We investigate the tunnel coupling between the outer p-type GaAsSb shell and the n-type InAs core in catalyst-free InAs/InP/GaAsSb core-dualshell nanowires. We present a device fabrication protocol based on wet-etching processes on selected areas of the nanostructures that enables multiple configurations of measurements in the same nanowire-based device (i.e. shell-shell, core-core and core-shell). Low-temperature (4.2 K) transport in the shell-shell configuration in nanowires with 5 nm-thick InP barrier reveals a weak negative differential resistance. Differently, when the InP barrier thickness is increased to 10 nm, this negative differential resistance is fully quenched. The electrical resistance between the InAs core and the GaAsSb shell, measured in core-shell configuration, is significantly higher with respect to the resistance of the InAs core and of the GaAsSb shell. The field effect, applied via a back-gate, has an opposite impact on the electrical transport in the core and in the shell portions. Our results show that electron and hole free carriers populate the InAs and GaAsSb regions respectively and indicate InAs/InP/GaAsSb core-dualshell nanowires as an ideal system for the investigation of the physics of interacting electrons and holes at the nanoscale. [Figure not available: see fulltext.].

In this work, we isolate individual wurtzite InAs nanowires and fabricate electrical contacts at both ends, exploiting the single nanostructures as building blocks to realize two different architectures of conductometric sensors: (a) the nanowire is drop-casted onto&mdash, supported by&mdash, a SiO2/Si substrate, and (b) the nanowire is suspended at approximately 250 nm from the substrate. We test the source-drain current upon changes in the concentration of humidity, ethanol, and NO2, using synthetic air as a gas carrier, moving a step forward towards mimicking operational environmental conditions. The supported architecture shows higher response in the mid humidity range (50% relative humidity), with shorter response and recovery times and lower detection limit with respect to the suspended nanowire. These experimental pieces of evidence indicate a minor role of the InAs/SiO2 contact area, hence, there is no need for suspended nanostructures to improve the sensing performance. Moreover, the sensing capability of single InAs nanowires for detection of NO2 and ethanol in the ambient atmosphere is reported and discussed.

InP-InAs-InP multi-shell nanowires (NWs) were grown in the wurtzite (WZ) or zincblende (ZB) crystal phase and their photoluminescence (PL) properties were investigated at low temperature (?6 K) for different measurement geometries. PL emissions from the NWs were carefully studied in a wide energy range from 0.7 to 1.6 eV. The different features observed in the PL spectra for increasing energies are attributed to four distinct emitting domains of these nano-heterostructures: the InAs island (axially grown), the thin InAs capping shell (radially grown), the crystal-phase quantum disks arising from the coexistence of InP ZB and WZ segments in the same NW, and the InP portions of the NW. These results provide a useful frame for the rational implementation of InP-InAs-InP multi-shell NWs containing various quantum confined domains as polychromatic optically active components in nanodevices for quantum information and communication technologies.

Random assemblies of vertically aligned core&ndash, shell GaAs&ndash, AlGaAs nanowires displayed an optical response dominated by strong oscillations of the reflected light as a function of the incident angle. In particular, angle-resolved specular reflectance measurements showed the occurrence of periodic modulations in the polarization-resolved spectra of reflected light for a surprisingly wide range of incident angles. Numerical simulations allowed for identifying the geometrical features of the core&ndash, shell nanowires leading to the observed oscillatory effects in terms of core and shell thickness as well as the tapering of the nanostructure. The present results indicate that randomly displaced ensembles of nanoscale heterostructures made of III&ndash, V semiconductors can operate as optical metamirrors, with potential for sensing applications.

With the increasing interest in the potential benefits of nanotechnologies, concern is still growing that they may present emerging risks for workers. Various strategies have been developed to assess the exposure to nano-objects and their agglomerates and aggregates (NOAA) in the workplace, integrating different aerosol measurement instruments and taking into account multiple parameters that may influence NOAA toxicity. The present study proposes a multi-metric approach for measuring and sampling NOAA in the workplace, applied to three case studies in laboratories each dedicated to materials with different shapes and dimensionalities: graphene, nanowires, and nanoparticles. The study is part of a larger project with the aim of improving risk management tools in nanomaterials research laboratories. The harmonized methodology proposed by the Organization for Economic Cooperation and Development (OECD) has been applied, including information gathering about materials and processes, measurements with easy-to-use and hand-held real-time devices, air sampling with personal samplers, and off-line analysis using scanning electron microscopy. Significant values beyond which an emission can be attributed to the NOAA production process were identified by comparison of the particle number concentration (PNC) time series and the corresponding background levels in the three laboratories. We explored the relations between background PNC and microclimatic parameters. Morphological and elemental analysis of sampled filters was done to identify possible emission sources of NOAA during the production processes: rare particles, spherical, with average diameter similar to the produced NOAA were identified in the nanoparticles laboratory, so further investigation is recommended to confirm the potential for worker exposure. In conclusion, the information obtained should provide a valuable basis for improving risk management strategies in the laboratory at work.

It is well known that a significant lateral growth is observed in the InAsSb sections of InAs/InAsSb heterostructured nanowires (NWs) with intermediate Sb content that prevents the independent control of NW diameter and length. Here we demonstrate that this lateral growth can be suppressed by increasing the growth temperature of the InAsSb segment and by reducing the InAs stem length. Optimized InAsSb sections show good structural and electrical properties. The mechanism driving this reduced lateral growth and its relevance toward the synthesis of highly controlled InAs/InAsSb heterostructured NWs are discussed.

We demonstrate room-temperature strong coupling between a mid-infrared (? = 9.9 ?m) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k = 0 where - potentially - polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and - simultaneously - to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the strong critical coupling concept is highlighted. © 2014 AIP Publishing LLC.

Electronic Mach–Zehnder interferometers in the quantum Hall (QH) regime are currently discussed for the realization of quantum information schemes. A recently proposed device architecture employs interference between two co-propagating edge channels. Here we demonstrate the precise control of individual edge-channel trajectories in quantum point contact devices in the QH regime. The biased tip of an atomic force microscope is used as a moveable local gate to pilot individual edge channels. Our results are discussed in light of the implementation of multi-edge interferometers.

We investigate a growth mechanism which allows for the fabrication of catalyst-free InAs nanowires on Si (111) substrates by chemical beam epitaxy. Our growth protocol consists of successive low-temperature (LT) nucleation and high-temperature growth steps. This method produces non-tapered InAs nanowires with controllable length and diameter. We show that InAs nanowires evolve from the islands formed during the LT nucleation step and grow truly catalyst-free, without any indium droplets at the tip. The impact of different growth parameters on the nanowire morphology is presented. In particular, good control over nanowire aspect ratio is demonstrated. A better understanding of the growth process is obtained through the development of a theoretical model combining the diffusion-induced growth scenario with some specific features of the catalyst-free growth mechanism, along with the analysis of the V/III flow ratio influencing material incorporation. As a result, we perform a full mapping of the nanowire morphology versus growth parameters which provides useful general guidelines on the self-induced formation of III-V nanowires on silicon.

In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation. In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation. (C) 2015 Optical Society of America

We report on the demonstration of Terahertz (THz) broadband detectors based on field effect transistors exploiting tapered semiconductor nanowires. The intrinsic asymmetry provided by the nanowires geometry allows to achieve responsivity values as high as 55 V/W (2.5 mA/W) and a noise-equivalent-power of 3 x 10(-10) W/Hz(1/2) independent of the specific gate voltage applied. The possibility to reduce the number of terminals required to the source and drain contacts only and the technological feasibility of multi-pixel arrays are promising for the realization of compact and integrated THz matrix array detection systems. (C) 2014 AIP Publishing LLC.

The absorption properties of a resonator can be tuned by varying the phase between incoming coherent light beams. Such control is now shown under strong coupling conditions, allowing all incoming energy to be converted into polaritons. The ability to drive a system with an external input is a fundamental aspect of light–matter interaction. The key concept in many photonic applications is the ‘critical coupling’ condition1,2: at criticality, all the energy fed to the system is dissipated within the system itself. Although this idea was crucial to enhance the efficiency of many devices, it was never considered in the context of systems operating in a non-perturbative regime. In this so-called strong-coupling regime, the matter and light degrees of freedom are mixed into dressed states, leading to new eigenstates called polaritons3,4,5,6,7,8,9,10. Here we demonstrate that the strong-coupling regime and the critical coupling condition can coexist; in such a strong critical coupling situation, all the incoming energy is converted into polaritons. A general semiclassical theory reveals that such a situation corresponds to a special curve in the phase diagram of the coupled light–matter oscillators. In the case of a system with two radiating ports, the phenomenology shown is that of coherent perfect absorption (CPA; refs 11, 12), which is then naturally understood in the framework of critical coupling. Most importantly, we experimentally verify polaritonic CPA in a semiconductor-based intersubband-polariton photonic crystal resonator. This result opens new avenues in polariton physics, making it possible to control the pumping efficiency of a system independent of the energy exchange rate between the electromagnetic field and the material transition.

Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper, we report on a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals such as bandgaps and defect modes are exported to the metallic counterpart. Such a structure may have interesting applications in infrared science and technology, for instance, in quantum well infrared photodetectors, narrowband spectral filters, and tailorable thermal emitters.

The development of self-assembled nanostructure technologies has recently opened the way towards a wide class of semiconductor integrated devices, with progressively optimized performances and the potential for a widespread range of electronic and photonic applications. Here we report on the development of field effect transistors (FETs) based on semiconductor nanowires (NWs) as highly-sensitive room-temperature plasma-wave broadband terahertz (THz) detectors. The electromagnetic radiation at 0.3 THz is funneled onto a broadband bow-tie antenna, whose lobes are connected to the source and gate FET electrodes. The oscillating electric field experienced by the channel electrons, combined with the charge density modulation by the gate electrode, results in a source-drain signal rectification, which can be read as a DC signal output. We investigated the influence of Se-doping concentration of InAs NWs on the detection performances, reaching responsivity values higher than 100 V W-1, with noise-equivalent-power of similar to 10(-9) W Hz(-1/2). Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application.

The electrical properties of nanowire-based n-InSb-n-InAs heterojunctions were investigated theoretically and experimentally. Analysis of the current-voltage characteristics showed that the current through the heterojunction is caused mostly by generation-recombination processes in the InSb and at the heterointerface. Due to the partially overlapping valence band of InSb and the conduction band of InAs, the second process is fast and activationless. Theoretical analysis showed that, depending on the heterojunction parameters, the flux of non-equilibrium minority carriers may have a different direction, explaining the experimentally observed non-monotonic coordinate dependence of the electron beam induced current. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795123]

Millivolt range thermovoltage is demonstrated in single InAs-nanowire based field effect transistors. Thanks to a buried heating scheme, we drive both a large thermal bias DT>10K and a strong field-effect modulation of electric conductance on the nanostructures. This allows the precise mapping of the evolution of the Seebeck coefficient S as a function of the gate-controlled conductivity between room temperature and 100K$. Based on these experimental data a novel estimate of the electron mobility is given. This value is compared with the result of standard field-effect based mobility estimates and discussed in relation to the effect of charge traps in the devices., 6 pages, 4 figures

We report the growth of InAs/InAs1-xSbx single and double heterostructured nanowires by Au-assisted chemical beam epitaxy. The InAs1-xSbx nanowire segments have been characterized in a wide range of antimony compositions. Significant lateral growth is observed at intermediate compositions (x similar to 0.5), and the nucleation and step-flow mechanism leading to this lateral growth has been identified and described. Additionally, CuPt ordering of the alloy has been observed with high resolution transmission electron microscopy, and it is correlated to the lateral growth process. We also show that it is possible to regrow InAs above the InAsSb alloy segment, at least up to an intermediate antimony composition. Such double heterostructures might find applications both as mid-infrared detectors and as building blocks of electronic devices taking advantage of the outstanding electronic and thermal properties of antimonide compound semiconductors.

We report on the transition from the strong to the weak light-matter coupling regime between an intersubband excitation and a photonic crystal resonance in a nanostructured semiconductor membrane. Such a transition is induced by varying the intensity of an ultrafast light pulse, which is employed for pumping and probing the system eigenmodes. The phenomenon is interpreted in terms of the saturation of the intersubband transition due to the large number of photoexcited electrons in the quantum well, as confirmed by a thorough analysis performed both in frequency and time domain.

We report on the development of nanowire-based field-effect transistors operating as high sensitivity terahertz (THz) detectors. By feeding the 1.5 THz radiation field of a quantum cascade laser (QCL) at the gate-source electrodes with a wide band dipole antenna, we record a photovoltage signal corresponding to responsivity values >10 V/W, with impressive noise equivalent power levels

International audience; Heterostructured InAs/InSb nanowire (Nw) based field effect transistors (FET) have been fabricated and tested as Terahetz radiation detectors. While responsivity and noise equivalent power compare with the ones of InAs nanowire detectors, the presence of small-gap InSb semiconductor gives rise to interesting physical effects such an increase of the detected signal with charge injection through the wire, at odds with standard FET-detectors. Additionally, the photodetected signal voltage changes its sign after a threshold gate bias, which we explain considering surface-related transport and field asymmetries imposed by the use of a lateral gate electrode.

We report the fabrication and characterization of superconducting quantum interference devices (SQUIDs) based on InAs nanowires and vanadium superconducting electrodes. These mesoscopic devices are found to be extremely robust against thermal cycling and to operate up to temperatures of $\sim2.5$~K with reduced power dissipation. We show that our geometry allows to obtain nearly-symmetric devices with very large magnetic-field modulation of the critical current. All these properties make these devices attractive for on-chip quantum-circuit implementation., 3 pages, 3 figures

Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron-photon interaction are discussed. (C) 2011 American Institute of Physics. [doi :10.1063/1.3578341]

We report on the particle diameter dependence of the growth rate of the InSb segment of InAs-InSb heterostructured nanowires grown by chemical beam epitaxy. The analysis of the growth rate reveals that the growth is limited by the Gibbs–Thomson effect and the effect of NW lateral dimensions on the nucleation rate during the layer by layer growth. In the temperature range explored, the surface diffusion of adatoms toward the particle and the growth temperature are not affecting the growth rate.

Recent studies on ultrafast dynamics of solids and nanostructures using few-cycle electromagnetic transients in the far and mid infrared spectral regions are presented. We are able to excite with phase-locked wave forms reaching peak amplitudes beyond 1 V/Aring which are comparable to inner-atomic fields. At the same time, a quantum-limited sensitivity is approached in electro-optic detection. Such capabilities are promising a completely new access to the quantum properties of both condensed matter and light.

Phase-locked electromagnetic transients in the terahertz (THz) spectral domain have become a unique contact-free probe of the femtosecond dynamics of low-energy excitations in semiconductors. Access to their nonlinear response, however, has been limited by a shortage of sufficiently intense THz emitters. Here we introduce a novel high-field source for THz transients featuring peak amplitudes of up to 108 MV/cm. This facility allows us to explore the non-perturbative response of semiconductors to intense fields tailored with sub-cycle precision. In a first experiment intense transients drive Rabi-oscillations between excitonic states in Cu2O, implying exciting perspectives for future THz quantum optics. At electric fields beyond 10 MV/cm, we observe the breakdown of the power expansion of the nonlinear polarization in bulk semiconductors. Furthermore, we employ the intense magnetic field components of our transients to coherently control spin waves in antiferromagnetically ordered solids. Finally, intersubband cavity polaritons in semiconductor microcavities are exploited to push light-matter coupling to an unprecedented ultrastrong and sub-cycle regime.

In this work we demonstrate the achievement of light-matter strong coupling regime between an intersubband transition and the photonic bandlike mode supported by a metallic grating. Polaritonic resonances have been identified in the reflectivity spectra at 10 degrees incidence, with a clear anticrossing appearing when the photonic mode is tuned across the transition line. Experimental results are in good agreement with the simulations performed with a scattering-matrix approach. This cavity design can be further optimized and is likely to open the way to a new class of time-resolved measurements, as it allows pump-and-probe measurements to be performed in collinear geometries. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3524823]

We report on the morphology of InAs-InSb heterostructured nanowires grown by Au-assisted chemical beam epitaxy. Using scanning and transmission electron microscopy, along with high angle annular dark field image analysis, we show that the hexagons defining the cross section of the two segments of the nanowires are rotated one with respect to the other by 30° around the growth direction and that the corners of these hexagons are rounded off by six small facets. Six additional facets that are not parallel to the growth direction are found in the InSb segment at the InAs-InSb interface and are indexed. Finally, the relation between the dimensions of the two segments composing the nanowires is discussed quantitatively.

Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a femtosecond near-infrared pulse. Midinfrared probe transients trace the non-adiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. published

Intersubband cavity polaritons in a GaAs/AIGaAs quantum well waveguide structure are photogenerated by a 12-fs near-infrared pulse. Multi-THz field transients directly trace the non-adiabatic switch-on of light-matter coupling with a vacuum polariton splitting of up to 44% of the bare photon frequency. We study the decay of a coherent photon state during quasi-instantaneous switching with sub-cycle resolution.

Transport properties of high quality Nb/semiconductor/Nb long Josephson junctions based on metamorphic In_0.75Ga_0.25As epitaxial layers are reported. Different junction geometries and fabrication procedures are presented that allow a systematic comparison with quasiclassical theory predictions. The impact of junction transparency is highlighted and a procedure capable of yielding a high junction quality factor is identified., Comment: 11 pages, 3 figures

III-V semiconductor nanowires have attracted intensive research interest because of their promising optical and electronic properties that can be manipulated by tailoring nanowire composition and morphology. Therefore, it is crucial to measure and control the diameter distribution of the grown nanowires. In this study, we analyze the diameter distribution of Au-catalyzed InAs nanowires. Au colloidal nanoparticles dispersed on InAs (111) B substrates and nanoparticles obtained by the thermal annealing of Au films were used as catalysts for InAs nanowire growth. The annealing time and temperature, the thickness of the Au film and the colloid sizes were systematically varied not only to understand their influence on nanowire diameter distribution, but also to find the optimal parameters for realizing samples with uniform and controlled diameter distribution. Morphological characterization was performed by scanning electron microscopy measurements and the image analysis was carried out using in-house-developed automated image analysis software to accurately determine the diameter distribution of the nanowires. A description of the image analysis software is also presented. The thermal annealing of films turned out to be the most suitable method for uniformity and density control, while the colloidal nanoparticles yielded narrow and more reproducible diameter distributions.

The optical response of the intersubband excitation of multiple two-dimensional electron gases within a semiconductor microcavity has been studied through angle-dependent reflectance measurements. Using a resonator based on total internal reflection, a clear splitting of about 14 meV of the coupled intersubband cavity modes is observed from 10 K to room temperature, with resulting polaritonlike dispersion. The experimental findings are in good agreement with theoretical calculations performed in a transfer-matrix formalism.

Structure characterisation of interfaces is a field of widespread application of high resolution transmission electron microscopy for its very high spatial resolution. Specimen thickness and electron optical condition have a deep influence on the high resolution electron transmission microscopy image contrast. Hence, in many cases, the real structure of the sample can be understood from experimental images only by comparison with the relevant simulation. Moreover, the understanding of the contrast variation of a few A at an interface is a task in which even the use of simulation could not produce an unequivocal solution of the experimental result. In this paper high resolution transmission electron microscopy image simulations show that two monolayers of crystalline material buried at an amorphous–crystalline interface can be successfully revealed and interpreted. The simulated images reproduce the experimental results as obtained from the Al/Si–As/n-GaAs (001) heterostructure.

The Schottky barrier height at Al/n-In x Ga 1 -x As contacts (0.19 < x < 0.38) was engineered by fabricating Si bilayers at the metal-semiconductor interface. Si interlayers grown under As flux led to the suppression of the barrier, while interlayer deposition under Al flux yielded an increase in the barrier height. In situ X-ray photoemission spectroscopy results and ex situ current-voltage measurements indicated a barrier tunability range of about 0.8 eV, with ideal ohmic behavior of diodes engineered for low barrier height, and barrier heights as high as 0.7 eV in diodes engineered for high barrier height.

InSb-InAs nanowire heterostructure diodes investigated by electron beam induced current (EBIC) demonstrate an unusual spatial profile where the sign of the EBIC signal changes in the vicinity of the heterointerface. A qualitative explanation confirmed by theoretical calculations is based on the specific band diagram of the structure representing a type-III heterojunction with an accumulation layer in InAs. The sign of the EBIC signal depends on the specific parameters of this layer. In the course of measurements, the diffusion length of holes in InAs and its temperature dependence are also determined.

We report the realization of a hybrid superconductor-quantum dot device by means of top-down nanofabrication starting from a two dimensional electron gas in a InGaAs/InAlAs semiconductor heterostructure. The quantum dot is defined by electrostatic gates placed within the normal region of a planar Nb-InGaAs quantum well-Nb junction. Measurements in the regime of strong Coulomb blockade as well as cotunneling spectroscopy allow to directly probe the proximity-induced energy gap in a ballistic two-dimensional electron gas coupled to superconductors., 4 pages, 3 figures

Catalyst-assisted growth of semiconductor nanowires has opened up several new and exciting possibilities for low-dimensional semiconductor structures. The authors review progress on the realization of quantum dots in semiconductor nanowires, and their characterization by transport spectroscopy. Emphasis is placed on the wide range electronic properties exhibited due to flexibility of the growth process in terms of nanostructure composition and size. Particular attention is placed on studies of spin in few-electron quantum dots.

Multi-terahertz transients map out the photonic bandstructure of a plasmonic crystal while ultrastrong coupling with quantized electronic transitions in semiconductor quantum wells is activated within less than a cycle of light.