Conductance Quantization at zero magnetic field in InSb nanowires

Ballistic electron transport is a key requirement for existence of a topological phase transition in proximitized InSb nanowires. However, measurements of quantized conductance as direct evidence of ballistic transport have so far been obscured due to the increased chance of backscattering in one dimensional nanowires. We show that by improving the nanowire-metal interface as well as the dielectric environment we can consistently achieve conductance quantization at zero magnetic field. Additionally, studying the sub-band evolution in a rotating magnetic field reveals an orbital degeneracy between the second and third sub-bands for perpendicular fields above 1T

InAs/InSb: From nanowires to nanomembranes

Resumen del trabajo presentado al 16th European Microscopy Congress, celebrado en Lyon (Francia) del 28 de agosto al 2 de septiembre de 2016.The control over crystalline defects is of extreme importance when growing functional materials, since their presence may alter the final behavior (opto-electronic properties) and evolution of the growing system (orientation and shape). In the present work we address both phenomena in the particular case of InSb related nanostructures. On one hand, heterostructured architectures may show interfacial dislocations if reaching the coherency limit, which is dependent on geometrical constrictions of the systems in addition to the mismatch between phases. In this context, it is usually assumed that the mismatch strain in axial heterostructured nanowires is mainly relaxed by elastic distortion of the lattice, although theoretical calculations predict the formation of misfit dislocations. It is remarkably important unveiling whether the partial/total lattice relaxation takes place through elastic and/or plastic mechanisms since both will affect the material performance. Interestingly, the location and shape of the heterointerfaces, as well as possible diffusion phenomena involved, may hinder the understanding of the actual relaxation mechanism, as we show in the case of axial InAs/InSb nanowires. Contrary to most reported works, we find out the presence of misfit dislocations at the core of the system while there is a huge plane bending through the edges of the nanowires. On the other hand, we correlate the systematic observation of a lateral twin boundary with the morphological transition from nanowires to membrane-like systems, called nanosails. Based on the experimental data gathered, consisting on SEM and aberration-corrected STEM measurements, including polarity determination, we are able to establish the underlying defect-driving growth mechanism leading to the formation of membrane-like structures growing aside InAs/InSb nanowires, showing excellent transport properties. Possible instabilities during the growth may promote the sinking of the catalytic droplet to wet one sidewall, leading to the nucleation of the lateral twin that opens the way for the broadening of the system.We acknowledge funding from Generalitat de Catalunya 2014 SGR 1638 and the Spanish MINECO MAT2014-51480- ERC (e-ATOM) and Spanish MINECO Severo Ochoa Excellence Program.Peer Reviewe

Realization of microwave quantum circuits using hybrid superconducting-semiconducting nanowire Josephson elements

\u3cp\u3eWe report the realization of quantum microwave circuits using hybrid superconductor-semiconductor Josephson elements comprised of InAs nanowires contacted by NbTiN. Capacitively shunted single elements behave as transmon circuits with electrically tunable transition frequencies. Two-element circuits also exhibit transmonlike behavior near zero applied flux but behave as flux qubits at half the flux quantum, where nonsinusoidal current-phase relations in the elements produce a double-well Josephson potential. These hybrid Josephson elements are promising for applications requiring microwave superconducting circuits operating in a magnetic field.\u3c/p\u3

Revealing the band structure of InSb nanowires by high-field magnetotransport in the quasiballistic regime

International audienceThe charge transport properties of individual InSb nanowires based transistors are studied at 4.2 K in the quasiballistic regime. The energy level separations at zero magnetic field are extracted from a bias voltage spectroscopy. The magnetoconductance under a magnetic field applied perpendicularly to the nanowire axis is investigated up to 50 T. Owing to the magnetic reduction of the backscattering, the electronic states of the quasi-one-dimensional electron gas are revealed by Landauer-Büttiker conductance quantization. The results are compared to theoretical predictions revealing the spin and orbital degeneracy lifting. At sufficiently high magnetic field the measurements show the evolution to the quantum Hall effect regime with the formation of Landau orbits and conducting edge states

Influence of growth conditions on the performance of InP nanowire solar cells

International audienceNanowire based solar cells have attracted great attention due to their potential for high efficiency and low device cost. Photovoltaic devices based on InP nanowires now have characteristics comparable to InP bulk solar cells. A detailed and direct correlation of the influence of growth conditions on performance is necessary to improve efficiency further. We explored the effects of the growth temperature, and of the addition of HCl during growth, on the efficiency of nanowire array based solar cell devices. By increasing HCl, the saturation dark current was reduced, and thereby the nanowire solar cell efficiency was enhanced from less than 1% to 7.6% under AM 1.5 illumination at 1 sun. At the same time, we observed that the solar cell efficiency decreased by increasing the tri-methyl-indium content, strongly suggesting that these effects are carbon related

Efficiency Enhancement of InP Nanowire Solar Cells by Surface Cleaning

We demonstrate an efficiency enhancement of an InP nanowire (NW) axial p–n junction solar cell by cleaning the NW surface. NW arrays were grown with <i>in situ</i> HCl etching on an InP substrate patterned by nanoimprint lithography, and the NWs surfaces were cleaned after growth by piranha etching. We find that the postgrowth piranha etching is critical for obtaining a good solar cell performance. With this procedure, a high diode rectification factor of 10⁷ is obtained at ±1 V. The resulting NW solar cell exhibits an open-circuit voltage (<i>V</i>_oc) of 0.73 V, a short-circuit current density (<i>J</i>_sc) of 21 mA/cm², and a fill factor (FF) of 0.73 at 1 sun. This yields a power conversion efficiency of up to 11.1% at 1 sun and 10.3% at 12 suns

InSb Nanowires with Built-In Ga x In 1– x Sb Tunnel Barriers for Majorana Devices

International audienceMajorana zero modes (MZMs), prime candidates for topological quantum bits, are detected as zero bias conductance peaks (ZBPs) in tunneling spectroscopy measurements. Implementation of a narrow and hightunnel barrier in the next generation of Majorana devices can help to achieve the theoretically predicted quantized height of the ZBP.We propose a material-oriented approach to engineer a sharp and narrow tunnel barrier by synthesizing a thin axial segment of GaxIn1-xSb within an InSb nanowire. By varying the precursor molar fraction and the growth time, we accurately control the composition and the length of the barriers. Theheight and the width of the GaxIn1-xSbtunnel barrier areextracted from the Wentzel-Kramers-Brillouin (WKB)-fits to the experimentalI-V trace

InSb Nanowires with Built-In Ga_<i>x</i>In_1–<i>x</i>Sb Tunnel Barriers for Majorana Devices

Majorana zero modes (MZMs), prime candidates for topological quantum bits, are detected as zero bias conductance peaks (ZBPs) in tunneling spectroscopy measurements. Implementation of a narrow and high tunnel barrier in the next generation of Majorana devices can help to achieve the theoretically predicted quantized height of the ZBP. We propose a material-oriented approach to engineer a sharp and narrow tunnel barrier by synthesizing a thin axial segment of Ga_<i>x</i>In_1–<i>x</i>Sb within an InSb nanowire. By varying the precursor molar fraction and the growth time, we accurately control the composition and the length of the barriers. The height and the width of the Ga_<i>x</i>In_1–<i>x</i>Sb tunnel barrier are extracted from the Wentzel–Kramers-Brillouin (WKB) fits to the experimental <i>I</i>–<i>V</i> traces