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InSb nanowire (NW) arrays fabricated by a top-down etching process were investigated for multispectral infrared photodetection. A 2.5 μm thick film of InSb was grown on Si (100) by molecular beam epitaxy using an AlSb buffer layer to alleviate defects associated with lattice mismatch strain, as confirmed by scanning electron microscopy and x-ray diffraction. Using a Ti mask patterned by electron beam lithography, InSb NW arrays with diameters ranging from 300 to 1300 nm (100 nm steps) and pitches ranging from 1000 nm to 3500 (500 nm steps) were reactive ion etched from the thin film. For each 100 nm increase in NW diameter, the peak absorptance wavelength, as measured by Fourier transform infrared spectroscopy, increased by 0.53 ± 0.2 μm. The ability of InSb nanowires to produce highly tunable absorptance from 1.61 to 6.86 μm was demonstrated. [ABSTRACT FROM AUTHOR]

A betavoltaic device is reported that directly converts beta energy from a 63Ni 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. Monte Carlo simulations predict a betavoltaic efficiency in agreement with experimental results. The nanowire betavoltaic device can be used as a power source for nano-/micro-systems such as mobile electronic devices, implantable medical devices, and wireless sensor networks. [ABSTRACT FROM AUTHOR]

The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current Ic versus an axial magnetic field shows an unexpected modulation and persistence to fields T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed. [ABSTRACT FROM AUTHOR]

The native oxide at the surface of III−V nanowires, such as InAs, can be a major source of charge noise and scattering in nanowire-based electronics, particularly for quantum devices operated at low temperatures. Surface passivation provides a means to remove the native oxide and prevent its regrowth. Here, we study the effects of surface passivation and conformal dielectric deposition by measuring electrical conductance through nanowire field effect transistors treated with a variety of surface preparations. By extracting field effect mobility, subthreshold swing, threshold shift with temperature, and the gate hysteresis for each device, we infer the relative effects of the different treatments on the factors influencing transport. It is found that a combination of chemical passivation followed by deposition of an aluminum oxide dielectric shell yields the best results compared to the other treatments, and comparable to untreated nanowires. Finally, it is shown that an entrenched, top-gated device using an optimally treated nanowire can successfully form a stable double quantum dot at low temperatures. The device has excellent electrostatic tunability owing to the conformal dielectric layer and the combination of local top gates and a global back gate. [ABSTRACT FROM AUTHOR]

Vertically oriented and ordered GaAs nanowire arrays have been grown by the self-assisted mechanism using substrates prepared with nano-patterned oxide templates. Patterned Ga-assisted GaAs nanowire growth on (111) silicon by molecular beam epitaxy showed that the axial and radial growth rates increased with increasing interhole spacing. A model is described which accounts for the correlation of the final length and diameter with pattern pitch. The model considers that growth material is supplied by a secondary flux of both gallium and arsenic adatoms desorbing from the oxide surface between the nanowires which subsequently impinge on the liquid droplet and nanowire sidewalls. We show that shading of the incident and scattered flux by neighboring nanowires in the array can strongly affect the axial and radial growth rates, leading to significant differences in final nanowire morphologies. [ABSTRACT FROM AUTHOR]

An experimental approach to achieving phase purity in nanowires through molecular beam epitaxy growth is presented. Superlattice heterostructured nanowires were grown, consisting of alternating layers of GaAsP and GaP. The observed core-multishell heterostructure, extending axially and radially, is attributed to simultaneous Au-assisted vertical growth and diffusion-limited radial growth along lateral nanowire facets. Growth interruptions at the GaAsP/GaP interfaces allowed for the elimination of stacking faults and the growth of nanowires with a single-crystalline wurtzite phase. [ABSTRACT FROM AUTHOR]