Characterization of Ambipolar GaSb/InAs Core–Shell Nanowires by Thermovoltage Measurements

Gluschke, Jan G.; Leijnse, Martin; Ganjipour, Bahram; Dick, Kimberly A.; Linke, Heiner; Thelander, Claes

doi:10.1021/acsnano.5b01495

Cited by 15 publications

(12 citation statements)

References 40 publications

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“…Thermoelectric transport in CSNs has been already studied in a couple of experimental papers. One recent work was the characterization of GaAs/InAs nanowires by thermovoltage measurements in those situations when electrical conductance does not provide information [30]. Another study demonstrated enhanced thermoelectric properties in Bi/Te CSNs via strain effects [31].…”

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confidence: 99%

Reversal of Thermoelectric Current in Tubular Nanowires

et al. 2017

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We calculate the charge current generated by a temperature bias between the two ends of a tubular nanowire. We show that in the presence of a transversal magnetic field the current can change sign, i.e., electrons can either flow from the hot to the cold reservoir, or in the opposite direction, when the temperature bias increases. This behavior occurs when the magnetic field is sufficiently strong, such that Landau and snaking states are created, and the energy dispersion is nonmonotonic with respect to the longitudinal wave vector. The sign reversal can survive in the presence of impurities. We predict this result for core/shell nanowires, for uniform nanowires with surface states due to the Fermi level pinning, and for topological insulator nanowires. PACS numbers: 73.23.b, 73.50.Lw, 73.63.Nm, 73.50.Fqi A temperature gradient across a conducing material induces an energy gradient, which in turn results in particle transport. In an open circuit, where no net current flows, a voltage is then generated when two ends of a sample are maintained at different temperatures -this is the Seebeck effect and the linear voltage response is known as thermopower. The hotter particles have larger average kinetic energy, and the net particle flow is therefore generally from the hot to the cold side. The thermopower and thermoelectric current can be positive or negative, depending on the type of charge carriers, i.e., electrons or holes.In comparison to this macroscopic case, the thermopower at the nanoscale has special characteristics. For example, if the energy separation between the quantum states of the system is larger than the thermal energy the thermopower may alternate between positive and negative values, depending on the position of the Fermi level relatively to a resonant energy, which can be controlled with a gate voltage. These oscillations were predicted a long time ago [1], and subsequently experimentally observed in quantum dots [2][3][4], and in molecules [5]. A sign change in the thermopower can also be obtained by increasing the temperature gradient and thus the population of the resonant level [6][7][8][9]. In these examples the charge carriers are electrons and the sign change of the thermopower means that they travel from the cold side to the hot side, which may appear counterintuitive. Other nonlinear effects can occur if the characteristic relaxation length of electrons and or phonons exceeds the sample size [10], because the energy of electrons and/or phonons is no longer controlled by the temperature of the bath, but by the generated electric bias, including Coulomb interactions [11,12].Observing such negative thermopower at the nanoscale is difficult for at least two reasons: the currents tend to be small and it is hard to maintain a constant temperature difference across such short distances. Here we argue that a generic class of tubular nanowires, to be defined in more detail below, are ideal systems for both realizing and observing negative thermopower. Semiconductor nanowires are versatile syst...

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Reversal of Thermoelectric Current in Tubular Nanowires

et al. 2017

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“…Starting with the conductance trace as a function of back-gate voltage [Fig. 3(c)], we observe that the InAs reference nanowire (green) becomes depleted for negative gate voltages, whereas the core-shell nanowire (blue) shows ambipolar behavior as a result of an onset of hole transport in the GaSb shell for V g < 0 V. 24 Charge stability diagrams were recorded for both devices, and they are shown in Figs. 3(d)-(f).…”

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confidence: 99%

Electron-hole interactions in coupled InAs-GaSb quantum dots based on nanowire crystal phase templates

et al. 2016

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We report growth and characterization of a coupled quantum dot structure that utilizes nanowire templates for selective epitaxy of radial heterostructures. The starting point is a zinc blende InAs nanowire with thin segments of wurtzite structure. These segments have dual roles: they act as tunnel barriers for electron transport in the InAs core, and they also locally suppress growth of a GaSb shell, resulting in coaxial InAs-GaSb quantum dots with integrated electrical probes. The parallel quantum dot structure hosts spatially separated electrons and holes that interact due to the type-II broken gap of InAs-GaSb heterojunctions. The Coulomb blockade in the electron and hole transport is studied, and periodic interactions of electrons and holes are observed and can be reproduced by modeling. Distorted Coulomb diamonds indicate voltage-induced ground-state transitions, possibly a result of changes in the spatial distribution of holes in the thin GaSb shell. Coupled quantum dots (QDs) represent a model system for studies of charge carrier interactions, and are the heart of most schemes for spin-based quantum computation.

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“…In addition to the QWs, InAs/GaSb core-shell nanowires (NWs) have been investigated both experimentally and theoretically. [5][6][7][8][9][10][11][12][13][14][15] Core-shell NWs with one shell are grown by several groups today, [8][9][10][11][12][13][14][15][16] and NWs with two shells can be grown, 16 e.g., for the reason of a passivating outer layer on InAs. 14 In this work we study core-shell-shell NWs, where an insulator core is radially overgrown with one InAs and one GaSb layer, see Fig.…”

Section: Introductionmentioning

confidence: 99%

“…BHZ parameters used in Fig.2(b). The rest of the parameters appearing in Eqs (9)(10)(11)(12). are set to zero.…”

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Band structure and end states in InAs/GaSb core-shell-shell nanowires

et al. 2020

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Quantum wells in InAs/GaSb heterostructures can be tuned to a topological regime associated with the quantum spin Hall effect, which arises due to an inverted band gap and hybridized electron and hole states. Here, we investigate electron-hole hybridization and the fate of the quantum spin Hall effect in a quasi one-dimensional geometry, realized in a core-shell-shell nanowire with an insulator core and InAs and GaSb shells. We calculate the band structure for an infinitely long nanowire using k • p theory within the Kane model and the envelope function approximation, then map the result onto a BHZ model which is used to investigate finite-length wires. Clearly, quantum spin Hall edge states cannot appear in the core-shell-shell nanowires which lack onedimensional edges, but in the inverted band-gap regime we find that the finite-length wires instead host localized states at the wire ends. These end states are not topologically protected, they are four-fold degenerate and split into two Kramers pairs in the presence of potential disorder along the axial direction. However, there is some remnant of the topological protection of the quantum spin Hall edge states in the sense that the end states are fully robust to (time-reversal preserving) angular disorder, as long as the bulk band gap is not closed.

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Characterization of Ambipolar GaSb/InAs Core–Shell Nanowires by Thermovoltage Measurements

Cited by 15 publications

References 40 publications

Reversal of Thermoelectric Current in Tubular Nanowires

Reversal of Thermoelectric Current in Tubular Nanowires

Electron-hole interactions in coupled InAs-GaSb quantum dots based on nanowire crystal phase templates

Band structure and end states in InAs/GaSb core-shell-shell nanowires

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