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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.

We demonstrate high-temperature thermoelectric conversion in InAs/InP nanowire quantum dots by taking advantage of their strong electronic confinement. The electrical conductance G and the thermopower S are obtained from charge transport measurements and accurately reproduced with a theoretical model accounting for the multi-level structure of the quantum dot. Notably, our analysis does not rely on the estimate of co-tunnelling contributions since electronic thermal transport is dominated by multi-level heat transport. By taking into account two spin-degenerate energy levels we are able to evaluate the electronic thermal conductance K and investigate the evolution of the electronic figure of merit ZT as a function of the quantum dot configuration and demonstrate ZT ~ 35 at 30 K, corresponding to an electronic effciency at maximum power close to the Curzon- Ahlborn limit., 7 pages, 4 figures

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.

We report results on the control of barrier transparency in InAs/InP nanowire quantum dots via the electrostatic control of the device electron states. Recent works demonstrated that barrier transparency in this class of devices displays a general trend just depending on the total orbital energy of the trapped electrons. We show that a qualitatively different regime is observed at relatively low filling numbers, where tunneling rates are rather controlled by the axial configuration of the electron orbital. Transmission rates versus filling are further modified by acting on the radial configuration of the orbitals by means of electrostatic gating, and the barrier transparency for the various orbitals is found to evolve as expected from numerical simulations. The possibility to exploit this mechanism to achieve a controlled continuous tuning of the tunneling rate of an individual Coulomb blockade resonance is discussed., Comment: 7 pages, 5 figures, plus SI

Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing. In this context, unveiling the fundamental parameters of the crystal phase structure is of much relevance for several applications. Here, we report on the anisotropy of the g-factor tensor and diamagnetic coefficient in wurtzite/zincblende (WZ/ZB) crystal-phase quantum dots (QDs) realized in single InP nanowires. The WZ and ZB alternating axial sections in the NWs are identified by high-angle annular dark-field scanning transmission electron microscopy. The electron (hole) g-factor tensor and the exciton diamagnetic coefficients in WZ/ZB crystal-phase QDs are determined through micro-photoluminescence measurements at low temperature (4.2 K) with different magnetic field configurations, and rationalized by invoking the spin-correlated orbital current model. Our work provides key parameters for band gap engineering and spin states control in crystal-phase low-dimensional structures in nanowires., 10 pages, 5 figures

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.

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 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.

Increasing the ease and the rapidity of processing in micro and nanotechnology is an ongoing task, which is pursued in both the academic environment for investigation of novel systems and in industry for fabrication of complex circuits on a large scale. In the field of nanoelectronics, the major challenge is to demonstrate a feasible method for device implementation based on individual nanosize objects, such as nanowires, nanotubes and nanocrystals. However, integrating these small objects in a macroscopic circuit is a difficult task. So far, nanostructures have been wired by highly sophisticated techniques not suitable for large-scale integration in macroscopic circuits, such as electron-beam lithography or focused ion-beam deposition. Here we present a 'one-pot' and rapid approach to electrically interconnect individual nanowires from random spatial distribution, with high spatial and positioning resolution and a remarkable reduction in overall fabrication time with respect to the other expensive and laborious techniques. The reliability of such technique is demonstrated by implementing a single semiconductor nanowire device

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.

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]

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.

Very robust voltage-controlled spin transitions in few-electron quantum dots are demonstrated. Two lateral-gate electrodes patterned on opposite sides of an InAs/InP nanowire are used to apply a transverse electric field and tune orbital energy separation down to level-pair degeneracy. Transport measurements in this regime allow us to demonstrate the breakdown of the standard alternate up/down spin filling scheme and unambiguously show singlet-triplet spin transitions. The strong confinement of the present devices leads to a large energy gain for the observed anomalous spin configurations that exceeds 4 meV. As a consequence, this behavior is well visible even at temperatures exceeding T = 20 K. RI Pitanti, Alessandro/K-5547-2012

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.

The analysis of the performance and the very understanding of the physical mechanisms governing the behavior of nanostructured devices requires the detailed knowledge of all parameters of electronic systems confined in ever shrinking microdomains. The role of temperature and the investigation of heat transport in solidstate nanoscale systems are currently under the spotlight [1]. Electronic thermometers [2‐4], refrigerators [5‐8] and heat transistors [9] based on metallic and superconductor nanostructures were already demonstrated. Such devices are typically operated at subkelvin temperatures, where electron-phonon interaction is weak and, as a result, the relevant electronic temperature may significantly dier from that of the lattice (if at all defined). In this context, the ability to perform local measurements of the electronic temperature becomes highly desirable. While in metallic systems superconducting tunnel junctions are routinely employed for this purpose, for the case of two-dimensional electron gases (2DEGs) or semiconductor nanowires at thermal equilibrium, quantum dots (QDs) were shown to be suitable for absolute thermometry [10, 11], due to the fact that in these conditions the linewidth of zero-bias Coulomb blockade (CB) peaks in the weak-coupling regime is directly related to the electronic temperature of the leads. Here, we propose a method for the detection of the local electronic temperature in a 2DEG, based on the analysis of the CB-peak lineshape. We shall first discuss zero-bias transport through a weakly-coupled QD in the presence of a temperature bias and show that zerobias conductance measurements can be used to experimentally determine both temperature values. We shall then employ this technique to investigate energy relaxation mechanisms in an electronic microdomain defined electrostatically in a GaAs/AlGaAs heterostructure and heated by an externally-driven current. The domain is connected to the surrounding 2DEG regions through the QD and three quantum point contacts (QPCs). As a known heating power is delivered to the domain, conductance across the QD is probed and the steady-state temperature detected. The dependence of the measured electron temperature on heating power will also be studied for dierent values of the QPC resistances: as the coupling to the surrounding 2DEG regions is reduced, we observe the crossover from a regime where excess heat is carried away by hot quasiparticles tunneling through the QPCs to one where power exchange with lattice phonons dominates. We shall show that the latter mechanism follows the T 5 power law expected [12] for the screened electron-acoustic phonon piezoelectric interaction, and obtain a measurement of the relative coupling constant consistent with theoretical estimates [1, 13].

A scheme that allows all-electrical high-bandwidth readout of a cantilever deflection by means of an integrated interdigitated transducer is presented. The present approach takes advantage of the piezoelectricity of the chosen cantilever substrate material to generate and detect surface-acoustic-waves by means of an interdigitated transducer (IDT) and to determine cantilever deflections. We shall also show that the same IDT can be used to excite the oscillation modes of the lever. Our scheme is compatible with implementations exploiting wireless excitation and readout and in mass sensing applications. A scheme that allows all-electrical high-bandwidth readout of a cantilever deflection by means of an integrated interdigitated transducer is presented. The present approach takes advantage of the piezoelectricity of the chosen cantilever substrate material to generate and detect surface-acoustic-waves by means of an interdigitated transducer IDT and to determine cantilever deflections. We shall also show that the same IDT can be used to excite the oscillation modes of the lever. Our scheme is compatible with implementations exploiting wireless excitation and readout and in mass sensing applications.

We report the Pd-assisted chemical beam epitaxy growth of zinc blende InAs nanowires which are grown on InAs(111)A substrates by employing Pd octane- and hexadecane-thiolates as catalyst precursors. The structural properties of these nanowires are investigated by scanning and transmission electron microscopy. Furthermore, we demostrate the growth of InAs nanowires on patterned substrates by employing the Pd hexadecylthiolate precursors as a direct-write resist in electron beam lithography [1]. During the growth of InAs nanowires from Pd catalyst particles on InAs(111)A, two distinct classes of nanowires are observed with smooth or zigzagged sidewalls. We show that this is related to a bimodal distribution of the wire-tip diameter: above a critical diameter wires grow with smooth sidewalls, and below with zigzagged morphology. Transmission electron microscopy analysis shows that the catalyst particles at the tip of zigzagged wires are smooth and have a higher aspect ratio than those at the tip of smooth wires. Zigzagged wires grow from liquid particles in the vapor– liquid–solid (VLS) mode whereas the smooth ones grow from solid particles in the vapor–solid– solid (VSS) mode [2].

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.

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.

We observed stimulated emission originating from light-hole transitions in single Zn 1 − x Cd x Se quantum-well structures, using high excitation photoluminescence spectroscopy as a function of temperature and cavity length. We found that the lasing wavelength depends on the cavity length, and can be switched by varying the sample temperature. The occurrence of lasing from light-hole recombinations in short cavities is also accompanied by an increase in the threshold of stimulated emission, with respect to larger cavities.

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