186 research outputs found
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
Thermoelectric power factor limit of a 1D nanowire
In the past decade, there has been significant interest in the potentially
advantageous thermoelectric properties of one-dimensional (1D) nanowires, but
it has been challenging to find high thermoelectric power factors based on 1D
effect in practice. Here we point out that there is an upper limit to the
thermoelectric power factor of non-ballistic 1D nanowires, as a consequence of
the recently established quantum bound of thermoelectric power output. We
experimentally test this limit in quasi-ballistic InAs nanowires by extracting
the maximum power factor of the first 1D subband through I-V characterization,
finding that the measured maximum power factors conform to the theoretical
limit. The established limit predicts that a competitive power factor, on the
order of mW/m-K^2, can be achieved by a single 1D electronic channel in
state-of-the-art semiconductor nanowires with small cross-section and high
crystal quality
Electron-hole interactions in coupled InAs-GaSb quantum dots based on nanowire crystal phase templates
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.Comment: 8 pages, 7 figure
Single-electron transport in InAs nanowire quantum dots formed by crystal phase engineering
We report electrical characterization of quantum dots formed by introducing
pairs of thin wurtzite (WZ) segments in zinc blende (ZB) InAs nanowires.
Regular Coulomb oscillations are observed over a wide gate voltage span,
indicating that WZ segments create significant barriers for electron transport.
We find a direct correlation of transport properties with quantum dot length
and corresponding growth time of the enclosed ZB segment. The correlation is
made possible by using a method to extract lengths of nanowire crystal phase
segments directly from scanning electron microscopy images, and with support
from transmission electron microscope images of typical nanowires. From
experiments on controlled filling of nearly empty dots with electrons, up to
the point where Coulomb oscillations can no longer be resolved, we estimate a
lower bound for the ZB-WZ conduction-band offset of 95 meV.Comment: 9 pages 9 figure
Electrical properties of InAs1âxSbx and InSb nanowires grown by molecular beam epitaxy
Results of electrical characterization of Au nucleated InAsâËâSbânanowiresgrown 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 xâ=â0.13. Pure InSbnanowires on the other hand show considerably lower, and strongly diameter dependent, mobility values. Finally, InAs of wurtzite crystal phase overgrown with an InAsâËâSbâ 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
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
Spectroscopy and level detuning of few-electron spin states in parallel InAs quantum dots
We use tunneling spectroscopy to study the evolution of few-electron spin
states in parallel InAs nanowire double quantum dots (QDs) as a function of
level detuning and applied magnetic field. Compared to the much more studied
serial configuration, parallel coupling of the QDs to source and drain greatly
expands the probing range of excited state transport. Owing to a strong
confinement, we can here isolate transport involving only the very first
interacting single QD orbital pair. For the (2,0)-(1,1) charge transition, with
relevance for spin-based qubits, we investigate the excited (1,1) triplet, and
hybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits
the (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet,
we clearly resolve transport through all triplet states near the avoided
singlet-triplet crossings. Transport calculations, based on a simple model with
one orbital on each QD, fully replicate the experimental data. Finally, we
observe an expected mirrored symmetry between the 1-2 and 2-3 electron
transitions resulting from the two-fold spin degeneracy of the orbitals.Comment: 17 pages, 8 figure
A quantum-dot heat engine operating close to the thermodynamic efficiency limits
Cyclical heat engines are a paradigm of classical thermodynamics, but are
impractical for miniaturization because they rely on moving parts. A more
recent concept is particle-exchange (PE) heat engines, which uses energy
filtering to control a thermally driven particle flow between two heat
reservoirs. As they do not require moving parts and can be realized in
solid-state materials, they are suitable for low-power applications and
miniaturization. It was predicted that PE engines could reach the same
thermodynamically ideal efficiency limits as those accessible to cyclical
engines, but this prediction has not been verified experimentally. Here, we
demonstrate a PE heat engine based on a quantum dot (QD) embedded into a
semiconductor nanowire. We directly measure the engine's steady-state electric
power output and combine it with the calculated electronic heat flow to
determine the electronic efficiency . We find that at the maximum power
conditions, is in agreement with the Curzon-Ahlborn efficiency and that
the overall maximum is in excess of 70 of the Carnot efficiency
while maintaining a finite power output. Our results demonstrate that
thermoelectric power conversion can, in principle, be achieved close to the
thermodynamic limits, with direct relevance for future hot-carrier
photovoltaics, on-chip coolers or energy harvesters for quantum technologies
Electrical control of spins and giant g-factors in ring-like coupled quantum dots
Emerging theoretical concepts for quantum technologies have driven a
continuous search for structures where a quantum state, such as spin, can be
manipulated efficiently. Central to many concepts is the ability to control a
system by electric and magnetic fields, relying on strong spin-orbit
interaction and a large g-factor. Here, we present a new mechanism for spin and
orbital manipulation using small electric and magnetic fields. By hybridizing
specific quantum dot states at two points inside InAs nanowires, nearly perfect
quantum rings form. Large and highly anisotropic effective g-factors are
observed, explained by a strong orbital contribution. Importantly, we find that
the orbital and spin-orbital contributions can be efficiently quenched by
simply detuning the individual quantum dot levels with an electric field. In
this way, we demonstrate not only control of the effective g-factor from 80 to
almost 0 for the same charge state, but also electrostatic change of the ground
state spin
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