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...

We report on the optical investigation of single electron spins bound to fluorine donor impurities in ZnSe. Measurements of photon antibunching establish the presence of single, isolated optical emitters, and magnetooptical studies are consistent with the presence of an exciton bound to the spin-impurity complex. The isolation of this single donor-bound exciton complex and its potential homogeneity offer promising prospects for a scalable semiconductor qubit with an optical interface.PACS numbers: 78.55. Et, Schemes for quantum information processing and quantum communications rely on scalable, robust qubits. In particular, there are many proposals that require fast, efficient, and homogenous single-photon sources 1-3 and still others that rely on the interaction between matter qubits and flying photonic qubits 4 . The requisites for both types of schemes can be satisfied with semiconductor electron spins, which serve as single photon sources 5 or long lived quantum memories with an optical interface 6-8 . However, optical schemes, particularly those based on entanglement, also require large numbers of homogenous photon emitters 9-14 . Electron spins in self-assembled QDs, unfortunately, suffer from large inhomogenities due to their natural size distribution.Impurity-bound electrons in direct bandgap semiconductors, however, have relatively little inhomogeneous broadening 15-20 , yet still possess strong optical transitions when binding an additional exciton 18-21 and long ground state coherence times 7 .An electron bound to a single fluorine donor in ZnSe (F:ZnSe) may serve as a physical qubit with many potential advantages over previously researched qubits. F:ZnSe is particularly appealing because of its nuclear structure compared to III-V-based bound-exciton or quantum dot systems. Unlike III-V systems, isotopic purification of the ZnSe-host matrix to a nuclear-spin-0 background is possible, eliminating magnetic noise from nuclear spin diffusion 22,23 . Further, the F-impurity has a nuclear spin of 1/2 with 100% abundance. Electronnuclear spin swapping schemes 24,25 can be used, which, in combination with the spin-0 background of the isotopically purified host matrix, could lead to an extremely long-lived qubit. Additionally, the applicability of standard microfabrication techniques 26,27 to ZnSe makes the F:ZnSe system particularly scalable.The F:ZnSe system has already shown promise as a scalable source of single photons in Ref. 20. However, a) Electronic address: kdegreve@stanford.edu b) Currently at HRL Laboratories, LLC, 3011 Malibu Canyon Rd., Malibu, CA 90265.this work did not demonstrate the potential of the donor system as a future quantum memory. Here, we show both statistics for single photon emission, as well as the presence of a three-level optical Λ-system through magnetospectroscopy experiments. This introduces F:ZnSe as a valid candidate for use as a scalable qubit with an optical interface.~ 23 meV TES I 2 FE-LH FE-HH c) pump D 0 X D 0 1s 2s,2p I 2 2s-TES 21 meV b) Zn 0.92 Mg 0.08 Se Zn 0.92 M...

Excitons bound to flourine atoms in ZnSe have the potential for several quantum optical applications. Examples include optically accessible quantum memories for quantum information processing and lasing without inversion. These applications require the bound-exciton transitions to be coupled to cavities with high cooperativity factors, which results in the experimental observation of low-threshold lasing. We report such lasing from fluorine-doped ZnSe quantum wells in 3 and 6 micron microdisk cavities. Photoluminescence and selective photoluminescence spectroscopy confirm that the lasing is due to bound-exciton transitions.Comment: 4 pages, 3 figures; introduction rewritte

We investigate different processes for optimizing the formation of Ohmic contacts to InAs nanowires. The nanowires are grown via molecular beam epitaxy without the use of metal catalysts. Metallic contacts are attached to the nanowires by using an electron beam lithography process. Before deposition of the contacts, the InAs nanowires are treated either by wet etching in an ammonium polysulfide (NH(4))(2)S(x) solution or by an argon milling process in order to remove a surface oxide layer. Two-point electrical measurements show that the resistance of the ammonium polysulfide-treated nanowires is two orders of magnitude lower than that of the untreated nanowires. The nanowires that are treated by the argon milling process show a resistance which is more than an order of magnitude lower than that of those treated with ammonium polysulfide. Four-point measurements allow us to extract an upper bound of 1.4 × 10(-7) Ω cm(2) for the contact resistivity of metallic contacts on nanowires treated by the argon milling process.