Analysis of Nanowire pn-Junction with Combined Current-Voltage, Electron-Beam-Induced Current, Cathodoluminescence, and Electron Holography Characterization.

We present the characterization of a pn-junction GaAs nanowire. For the characterization, current-voltage, electron-beam-induced current, cathodoluminescence, and electron holography measurements are used. We show that by combining information from these four methods, in combination with drift-diffusion modelling, we obtain a detailed picture of how the nanowire pn-junction is configured and how the recombination lifetime varies axially in the nanowire.

Detection of Be dopant pairing in VLS grown GaAs nanowires with twinning superlattices.

Control over the distribution of dopants in nanowires is essential for regulating their electronic properties, but perturbations in nanowire microstructure may affect doping. Conversely, dopants may be used to control nanowire microstructure including the generation of twinning superlattices (TSLs)-periodic arrays of twin planes. Here the spatial distribution of Be dopants in a GaAs nanowire with a TSL is investigated using atom probe tomography.

off-axis electron holography of real-time dopant diffusion in GaAs nanowires.

Off-axis electron holography was used to reveal remote doping in GaAs nanowires occurring duringannealing in a transmission electron microscope. Dynamic changes to the electrostatic potential caused by carbon dopant diffusion upon annealing were measured across GaAs nanowires with radial p-p+ core-shell junctions. Electrostatic potential profiles were extracted from holographic phase maps and built-in potentials () and depletion layer widths (DLWs) were estimated as function of temperature over 300-873 K.

Doping Profiles in Ultrathin Vertical VLS-Grown InAs Nanowire MOSFETs with High Performance.

Thin vertical nanowires based on III-V compound semiconductors are viable candidates as channel material in metal oxide semiconductor field effect transistors (MOSFETs) due to attractive carrier transport properties. However, for improved performance in terms of current density as well as contact resistance, adequate characterization techniques for resolving doping distribution within thin vertical nanowires are required. We present a novel method of axially probing the doping profile by systematically changing the gate position, at a constant gate length of 50 nm and a channel diameter of 12 nm, along a vertical nanowire MOSFET and utilizing the variations in threshold voltage shift (∼100 mV).

Superconductivity and Parity Preservation in As-Grown In Islands on InAs Nanowires.

We report synthesis of crystalline indium islands on InAs nanowires grown by molecular beam epitaxy. Structural analysis by transmission electron microscopy showed that In crystals grew in a tetragonal body-centered crystal structure within two families of orientations relative to wurtzite InAs. The crystalline islands had lengths < 500 nm and low-energy surfaces, suggesting that growth was driven mainly by surface energy minimization.

Highly Transparent Gatable Superconducting Shadow Junctions.

Gate-tunable junctions are key elements in quantum devices based on hybrid semiconductor-superconductor materials. They serve multiple purposes ranging from tunnel spectroscopy probes to voltage-controlled qubit operations in gatemon and topological qubits. Common to all is that junction transparency plays a critical role.

Shadow Epitaxy for In Situ Growth of Generic Semiconductor/Superconductor Hybrids.

Uniform, defect-free crystal interfaces and surfaces are crucial ingredients for realizing high-performance nanoscale devices. A pertinent example is that advances in gate-tunable and topological superconductivity using semiconductor/superconductor electronic devices are currently built on the hard proximity-induced superconducting gap obtained from epitaxial indium arsenide/aluminum heterostructures. Fabrication of devices requires selective etch processes; these exist only for InAs/Al hybrids, precluding the use of other, potentially superior material combinations.

Evolution of intermetallic GaPd/SiO catalyst and optimization for methanol synthesis at ambient pressure.

The CO hydrogenation to methanol is efficiently catalyzed at ambient pressure by nanodispersed intermetallic GaPd/SiO catalysts prepared by incipient wetness impregnation. Here we optimize the catalyst in terms of metal content and reduction temperature in relation to its catalytic activity. We find that the intrinsic activity is higher for the GaPd/SiO catalyst with a metal loading of 13 wt.

Superconducting vanadium/indium-arsenide hybrid nanowires.

We report MBE synthesis of InAs/vanadium hybrid nanowires. The vanadium was deposited without breaking ultra-high vacuum after InAs nanowire growth, minimizing any effect of oxidation and contamination at the interface between the two materials. We investigated four different substrate temperatures during vanadium deposition, ranging from -150 °C to 250 °C.

GaP nanowire betavoltaic device.

A betavoltaic device is reported that directly converts beta energy from a Ni radioisotope into electrical energy by impact ionization in a GaP nanowire array. The GaP nanowires are grown in a periodic array by molecular beam epitaxy on silicon using the self-assisted vapor-liquid-solid method. By growing GaP nanowires with large packing fraction and length on the order of the maximum beta range, the nanowires can efficiently capture the betas with high energy conversion efficiency while using inexpensive Si substrates.

White Light Emission from Fluorescent SiC with Porous Surface.

We report for the first time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fluorescent SiC) layer containing a hybrid structure. The surface of fluorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20 nm thick AlO, the photoluminescence intensity from the porous layer was significant enhanced by a factor of more than 12.

Stable amorphous georgeite as a precursor to a high-activity catalyst.

Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable--and hence little known and largely ignored--georgeite. The first three of these minerals are widely used as catalyst precursors for the industrially important methanol-synthesis and low-temperature water-gas shift (LTS) reactions, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase is usually zincian malachite.