Persistent enhancement of the carrier density in electron irradiated InAs nanowires

We report a significant and persistent enhancement of the conductivity in free-standing non intentionnaly doped InAs nanowires upon irradiation in ultra high vacuum. Combining four-point probe transport measurements performed on nanowires with different surface chemistries, field-effect based measurements and numerical simulations of the electron density, the change of the conductivity is found to be caused by the increase of the surface free carrier concentration. Although an electron beam of a few keV, typically used for the inspection and the processing of materials, propagates through the entire nanowire cross-section, we demonstrate that the nanowire electrical properties are predominantly affected by radiation-induced defects occuring at the nanowire surface and not in the bulk.Comment: 18 pages, 5 figure

Engineering the side facets of vertical [100] oriented InP nanowires for novel radial heterostructures

In addition to being grown on industry-standard orientation, vertical [100] oriented nanowires present novel families of facets and related cross-sectional shapes. These nanowires are engineered to achieve a number of facet combinations and cross-sectional shapes, by varying their growth parameters within ranges that facilitate vertical growth. In situ post-growth annealing technique is used to realise other combinations that are unattainable solely using growth parameters. Two examples of possible novel radial heterostructures grown on these vertical [100] oriented nanowire facets are presented, demonstrating their potential in future applications

Unipolar and bipolar operation of InAs/InSb nanowire heterostructure field-effect transistors

We present temperature dependent electrical measurements on n-type InAs/InSb nanowireheterostructurefield-effect transistors. The barrier height of the heterostructure junction is determined to be 220 meV, indicating a broken bandgap alignment. A clear asymmetry is observed when applying a bias to either the InAs or the InSb side of the junction. Impact ionization and band-to-band tunneling is more pronounced when the large voltage drop occurs in the narrow bandgapInSb segment. For small negative gate-voltages, the InSb segment can be tuned toward p-type conduction, which induces a strong band-to-band tunneling across the heterostructucture junction.This work was carried out within the Nanometer Structure Consortium at Lund University and was supported by the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation

Electrical properties of InAs1−xSbx and InSb nanowires grown by molecular beam epitaxy

Results of electrical characterization of Au nucleated InAs₁ˍₓSbₓnanowiresgrown by molecular beam epitaxy are reported. An almost doubling of the extracted field effect mobility compared to reference InAsnanowires is observed for a Sb content of x = 0.13. Pure InSbnanowires on the other hand show considerably lower, and strongly diameter dependent, mobility values. Finally, InAs of wurtzite crystal phase overgrown with an InAs₁ˍₓSbₓ shell is found to have a substantial positive shift in threshold voltage compared to reference nanowires.This work received financial support from the Nanometer Structure Consortium at Lund University (nmC@LU), the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation (KAW). It also received financial support from the French National Research Agency (ANR), TERADOT project, under Contract No.ANR-11-JS04-002-01

Electrical properties of InAs1-xSbx and InSb nanowires grown by molecular beam epitaxy

Results of electrical characterization of Au nucleated InAs1-xSbx nanowires grown by molecular beam epitaxy are reported. An almost doubling of the extracted field effect mobility compared to reference InAs nanowires is observed for a Sb content of x = 0.13. Pure InSb nanowires on the other hand show considerably lower, and strongly diameter dependent, mobility values. Finally, InAs of wurtzite crystal phase overgrown with an InAs1-xSbx shell is found to have a substantial positive shift in threshold voltage compared to reference nanowires. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726037

Temperature dependence of GaSb overgrowth of tungsten on GaSb (001) substrates using MOVPE

We demonstrate GaSb overgrowth over tungsten patterns and that selective area epitaxy is achievable in the W/GaSb system. By controlling the facet growth at low temperatures, it is possible to embed a metal grating in a thin layer

Inhomogeneous Si-doping of gold-seeded InAs nanowires grown by molecular beam epitaxy

We have investigated in-situ Si doping of InAs nanowires grown by molecular beam epitaxy from gold seeds. The effectiveness of n-type doping is confirmed by electrical measurements showing an increase of the electron density with the Si flux. We also observe an increase of the electron density along the nanowires from the tip to the base, attributed to the dopant incorporation on the nanowire facets whereas no detectable incorporation occurs through the seed. Furthermore the Si incorporation strongly influences the lateral growth of the nanowires without giving rise to significant tapering, revealing the complex interplay between axial and lateral growth.This work was supported by the ANR through the Project No. ANR-11-JS04-002-01, and the Ministry of Higher Education and Research, Nord-Pas de Calais Regional Council and FEDER through the “Contrat de Projets Etat Region (CPER) 2007-2013.” P.C. is the recipient of an Australian Research Council Future Fellowship (project number FT120100498)

Magneto-transport Subbands Spectroscopy in InAs Nanowires

We report on magneto-transport measurements in InAs nanowires under large magnetic field (up to 55T), providing a direct spectroscopy of the 1D electronic band structure. Large modulations of the magneto-conductance mediated by an accurate control of the Fermi energy reveal the Landau fragmentation, carrying the fingerprints of the confined InAs material. Our numerical simulations of the magnetic band structure consistently support the experimental results and reveal key parameters of the electronic confinement.Comment: 13 Pages, 5 figure

Formation of Long Single Quantum Dots in High Quality InSb Nanowires Grown by Molecular Beam Epitaxy

We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO$_2$ substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ~700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Land\'e g-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ~300 $\mu$eV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices.Comment: 19 pages, 5 figure

Doping Incorporation in InAs nanowires characterized by capacitance measurements

Sn and Se dopedInAsnanowires are characterized using a capacitance-voltage technique where the threshold voltages of nanowirecapacitors with different diameter are determined and analyzed using an improved radial metal-insulator-semiconductor field-effect transistor model. This allows for a separation of doping in the core of the nanowire from the surface charge at the side facets of the nanowire. The data show that the doping level in the InAsnanowire can be controlled on the level between 2×10¹⁸ to 1×10¹⁹ cm¯³, while the surface charge density exceeds 5×10¹² cm¯² and is shown to increase with higher dopant precursor molar fraction.This work was supported by the Swedish Research Council, the Swedish Foundation for Strategic Research, VINNOVA, the EU-project NODE 015783 and the Knut and Alice Wallenberg Foundation