We report the growth of InAs 1−x Sb x nanowires (0 ≤ x ≤ 0.15) grown by catalyst-free molecular beam epitaxy on silicon (111) substrates. We observed a sharp decrease of stacking fault density in the InAs 1−x Sb x nanowire crystal structure with increasing antimony content. This decrease leads to a significant increase in the field-effect mobility, this being more than three times greater at room temperature for InAs 0.85 Sb 0.15 nanowires than InAs nanowires. * To whom correspondence should be addressed † London Centre for Nanotechnology, University College London, London WC1H 0AH, United Kingdom ‡ Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom 1 arXiv:1402.3489v1 [cond-mat.mtrl-sci] Feb 2014Semiconductor nanowires are leading candidates for future applications in a wide variety of electronic, photonic and sensing devices. 1,2 III-V compound semiconductor nanowires including InAs 3 and GaN 4,5 have a number of potential functional advantages over elemental semiconductor nanowires including high mobility and direct bandgap. Furthermore the magnitude of the bandgap can be modulated by exploiting ternary compound semiconductors (such as InAsP 6 and AlGaAs 7 ), allowing the creation of heterostructure nanowires with axially-or radially-modulated electronic properties. Such bandgap engineering is in principle a more powerful tool for nanowire-based devices than thin-film-based devices since the radial relaxation of strain in nanowires allows the growth of heterostructures whose constituent compounds are significantly lattice-mismatched. 8,9 The growth of compound semiconductor nanowires directly onto single crystal silicon wafers would be advantageous, 10,11 because (i) it would allow integration of nanowire devices with the established silicon CMOS technology; and (ii) silicon wafers are orders of magnitude cheaper than their compound semiconductor counterparts. Compound semiconductor nanowires are, however, typically grown using the "vapor-liquid-solid" technique in which gold nanoparticle catalysts seed the growth. Gold cannot be combined with silicon since it forms trap states in the silicon bandgap. 12-14 Nickel has also been used to catalyze InAs nanowire growth on silicon 15 but these nanowires are not functional for direct integration as they grow following random orientations with respect to the substrate. There have therefore been many reports of nanowire growth without the use of heterocatalytic nanoparticle seeds [16][17][18][19][20][21] . In the case of the widely-studied narrow-bandgap semiconductor InAs, however, the absence of a heterocatalyst results in the nanowires displaying very high densities of defects including stacking faults, twin boundaries and polytypism, i.e. uncontrolled axial modulation of the crystal structure between the zinc-blende (cubic) and the wurtzite (hexagonal) polytypes of InAs. 17,21 This in turn leads to an undesirable suppression of the electron mobility. 22 In this letter, we investigate an approa...

Recently the question of whether the D-Wave processors exhibit large-scale quantum behavior or can be described by a classical model has attracted significant interest. In this work we address this question by studying a 503 qubit D-Wave Two device in the "black box" model, i.e., by studying its input-output behavior. Our work generalizes an approach introduced in Boixo et al. [Nat. Commun. 4, 2067], and uses groups of up to 20 qubits to realize a transverse Ising model evolution with a ground state degeneracy whose distribution acts as a sensitive probe that distinguishes classical and quantum models for the D-Wave device. Our findings rule out all classical models proposed to date for the device and provide evidence that an open system quantum dynamical description of the device that starts from a quantized energy level structure is well justified, even in the presence of relevant thermal excitations and a small value of the ratio of the single-qubit decoherence time to the annealing time.

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