Self-catalyzed InAs nanowires grown on Si: the key role of kinetics on their morphology.

Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertical gate-all-around transistors. The complementary metal oxide semiconductor (CMOS) compatibility and the nanowire aspect ratio are two crucial parameters to consider. In this work, we optimize the InAs nanowire morphology by changing the growth mode from Vapor-Solid to Vapor-Liquid-Solid in a CMOS compatible process.

Integration of the Rhombohedral BiSb(0001) Topological Insulator on a Cubic GaAs(001) Substrate.

Bismuth-antimony alloy (BiSb) is the first reported 3D topological insulator (TI). Among many TIs reported to date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low-current spin-orbit-torque magnetoresistive random access memories. Nevertheless, the 2D integration of TIs on industrial standards is lacking.

Spin-Orbit Protection of Induced Superconductivity in Majorana Nanowires.

Spin-orbit interaction (SOI) plays a key role in creating Majorana zero modes in semiconductor nanowires proximity coupled to a superconductor. We track the evolution of the induced superconducting gap in InSb nanowires coupled to a NbTiN superconductor in a large range of magnetic field strengths and orientations. Based on realistic simulations of our devices, we reveal SOI with a strength of 0.

Split-Channel Ballistic Transport in an InSb Nanowire.

We report an experimental study of one-dimensional (1D) electronic transport in an InSb semiconducting nanowire. A total of three bottom gates are used to locally deplete the nanowire, creating a ballistic quantum point contact with only a few conducting channels. In a magnetic field, the Zeeman splitting of the corresponding 1D sub-bands is revealed by the emergence of conductance plateaus at multiples of e/h, yet we find a quantized conductance pattern largely dependent on the configuration of voltages applied to the bottom gates.

Ballistic Majorana nanowire devices.

Majorana modes are zero-energy excitations of a topological superconductor that exhibit non-Abelian statistics. Following proposals for their detection in a semiconductor nanowire coupled to an s-wave superconductor, several tunnelling experiments reported characteristic Majorana signatures. Reducing disorder has been a prime challenge for these experiments because disorder can mimic the zero-energy signatures of Majoranas, and renders the topological properties inaccessible.

Supercurrent Interference in Few-Mode Nanowire Josephson Junctions.

Junctions created by coupling two superconductors via a semiconductor nanowire in the presence of high magnetic fields are the basis for the potential detection, fusion, and braiding of Majorana bound states. We study NbTiN/InSb nanowire/NbTiN Josephson junctions and find that the dependence of the critical current on the magnetic field exhibits gate-tunable nodes. This is in contrast with a well-known Fraunhofer effect, under which critical current nodes form a regular pattern with a period fixed by the junction area.

Andreev molecules in semiconductor nanowire double quantum dots.

Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires.

Experimental phase diagram of zero-bias conductance peaks in superconductor/semiconductor nanowire devices.

Topological superconductivity is an exotic state of matter characterized by spinless p-wave Cooper pairing of electrons and by Majorana zero modes at the edges. The first signature of topological superconductivity is a robust zero-bias peak in tunneling conductance. We perform tunneling experiments on semiconductor nanowires (InSb) coupled to superconductors (NbTiN) and establish the zero-bias peak phase in the space of gate voltage and external magnetic field.

Ballistic superconductivity in semiconductor nanowires.

Semiconductor nanowires have opened new research avenues in quantum transport owing to their confined geometry and electrostatic tunability. They have offered an exceptional testbed for superconductivity, leading to the realization of hybrid systems combining the macroscopic quantum properties of superconductors with the possibility to control charges down to a single electron. These advances brought semiconductor nanowires to the forefront of efforts to realize topological superconductivity and Majorana modes.

Observation of Conductance Quantization in InSb Nanowire Networks.

Majorana zero modes (MZMs) are prime candidates for robust topological quantum bits, holding a great promise for quantum computing. Semiconducting nanowires with strong spin orbit coupling offer a promising platform to harness one-dimensional electron transport for Majorana physics. Demonstrating the topological nature of MZMs relies on braiding, accomplished by moving MZMs around each other in a certain sequence.

Hard Superconducting Gap in InSb Nanowires.

Topological superconductivity is a state of matter that can host Majorana modes, the building blocks of a topological quantum computer. Many experimental platforms predicted to show such a topological state rely on proximity-induced superconductivity. However, accessing the topological properties requires an induced hard superconducting gap, which is challenging to achieve for most material systems.

InSb Nanowires with Built-In GaInSb 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 GaInSb within an InSb nanowire.

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

Nanowire 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.

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.

High-Yield Growth and Characterization of ⟨100⟩ InP p-n Diode Nanowires.

Semiconductor nanowires are nanoscale structures holding promise in many fields such as optoelectronics, quantum computing, and thermoelectrics. Nanowires are usually grown vertically on (111)-oriented substrates, while (100) is the standard in semiconductor technology. The ability to grow and to control impurity doping of ⟨100⟩ nanowires is crucial for integration.

Twin-Induced InSb Nanosails: A Convenient High Mobility Quantum System.

Ultra narrow bandgap III-V semiconductor nanomaterials provide a unique platform for realizing advanced nanoelectronics, thermoelectrics, infrared photodetection, and quantum transport physics. In this work we employ molecular beam epitaxy to synthesize novel nanosheet-like InSb nanostructures exhibiting superior electronic performance. Through careful morphological and crystallographic characterization we show how this unique geometry is the result of a single twinning event in an otherwise pure zinc blende structure.

Towards high mobility InSb nanowire devices.

We study the low-temperature electron mobility of InSb nanowires. We extract the mobility at 4.2 K by means of field effect transport measurements using a model consisting of a nanowire-transistor with contact resistances.

Rationally designed single-crystalline nanowire networks.

Rational bottom-up assembly of nanowire networks may be a way to successfully continue the miniaturization in the semiconductor industry. A generic method is developed that ensures InSb nanowires meet under the optimal angle for the formation of single-crystalline structures, which represents a promising platform for the future random access memories based on Majorana fermions.

Formation and electronic properties of InSb nanocrosses.

Signatures of Majorana fermions have recently been reported from measurements on hybrid superconductor-semiconductor nanowire devices. Majorana fermions are predicted to obey special quantum statistics, known as non-Abelian statistics. To probe this requires an exchange operation, in which two Majorana fermions are moved around one another, which requires at least a simple network of nanowires.

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 in situ 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.

High optical quality single crystal phase wurtzite and zincblende InP nanowires.

We report single crystal phase and non-tapered wurtzite (WZ) and zincblende twinning superlattice (ZB TSL) InP nanowires (NWs). The NWs are grown in a metalorganic vapor phase epitaxy (MOVPE) reactor using the vapor-liquid-solid (VLS) mechanism and in situ etching with HCl at a high growth temperature. Our stacking fault-free WZ and ZB TSL NWs allow access to the fundamental properties of both NW crystal structures, whose optical and electronic behaviors are often screened by polytypism or incorporated impurities.

Quantized conductance in an InSb nanowire.

Ballistic one-dimensional transport in semiconductor nanowires plays a central role in creating topological and helical states. The hallmark of such one-dimensional transport is conductance quantization. Here we show conductance quantization in InSb nanowires at nonzero magnetic fields.