246 research outputs found
Mapping of Axial Strain in InAs/InSb Heterostructured Nanowires
The article presents a mapping of the residual strain along the axis of
InAs/InSb heterostructured nanowires. Using confocal Raman measurements, we
observe a gradual shift in the TO phonon mode along the axis of these
nanowires. We attribute the observed TO phonon shift to a residual strain
arising from the InAs/InSb lattice mismatch. We find that the strain is maximum
at the interface and then monotonically relaxes towards the tip of the
nanowires. We also analyze the crystal structure of the InSb segment through
selected area electron diffraction measurements and electron diffraction
tomography on individual nanowires.Comment: 14 pages, 5 figure
Electronic Band Structure of Wurtzite GaP Nanowires via Resonance Raman Spectroscopy
Raman measurements are performed on defect-free wurzite GaP nanowires.
Resonance Raman measurements are carried out over the excitation energy range
between 2.19 and 2.71 eV. Resonances at 2.38 eV and 2.67 eV of the E1(LO) mode
and at 2.67 eV of the A1(LO) are observed. The presence of these intensity
resonances clearly demonstrates the existence of energy states with Gamma_9hh
and Gamma_7V (Gamma_7C) symmetries of the valence (conduction) band and allows
to measure WZ phase GaP band energies at the Gamma point. In addition, we have
investigated temperature dependent resonant Raman measurements, which allowed
us to extrapolate the zero temperature values of Gamma point energies, along
with the crystal field and spin-orbit splitting energies. Above results provide
a feedback for refining available theoretical calculations to derive the
correct wurtzite III-V semiconductor band structure.Comment: 24 pages, 6 figure
Giant thermovoltage in single InAs-nanowire field-effect transistors
Millivolt range thermovoltage is demonstrated in single InAs-nanowire based
field effect transistors. Thanks to a buried heating scheme, we drive both a
large thermal bias DT>10K and a strong field-effect modulation of electric
conductance on the nanostructures. This allows the precise mapping of the
evolution of the Seebeck coefficient S as a function of the gate-controlled
conductivity between room temperature and 100K$. Based on these experimental
data a novel estimate of the electron mobility is given. This value is compared
with the result of standard field-effect based mobility estimates and discussed
in relation to the effect of charge traps in the devices.Comment: 6 pages, 4 figure
Large thermal biasing of individual gated nanostructures
We demonstrate a novel nanoheating scheme that yields very large and uniform
temperature gradients up to about 1K every 100nm, in an architecture which is
compatible with the field-effect control of the nanostructure under test. The
temperature gradients demonstrated largely exceed those typically obtainable
with standard resistive heaters fabricated on top of the oxide layer. The
nanoheating platform is demonstrated in the specific case of a short-nanowire
device.Comment: 6 pages, 6 figure
Strain induced band alignment in wurtzite-zincblende InAs heterostructured nanowires
We study band alignment in wurtzite-zincblende polytype InAs heterostructured
nanowires using temperature dependent resonance Raman measurements. Nanowires
having two different wurtzite fractions are investigated. Using visible
excitation wavelengths in resonance Raman measurements, we probe the electronic
band alignment of these semiconductor nanowires near a high symmetry point of
the Brillouin zone (E gap). The strain in the crystal structure, as
revealed from the shift of the phonon mode, explains the observed band
alignment at the wurtzite-zincblende interface. Our experimental results are
further supported by electronic structure calculations for such periodic
heterostructured interface.Comment: 18 pages, 10 figure
Se-doping dependence of the transport properties in CBE-grown InAs nanowire field effect transistors
We investigated the transport properties of lateral gate field effect transistors (FET) that have been realized by employing, as active elements, (111) B-oriented InAs nanowires grown by chemical beam epitaxy with different Se-doping concentrations. On the basis of electrical measurements, it was found that the carrier mobility increases from 103 to 104 cm2/(V × sec) by varying the ditertiarybutyl selenide (DtBSe) precursor line pressure from 0 to 0.4 Torr, leading to an increase of the carrier density in the transistor channel of more than two orders of magnitude. By keeping the DtBSe line pressure at 0.1 Torr, the carrier density in the nanowire channel measures ≈ 5 × 1017 cm-3 ensuring the best peak transconductances (> 100 mS/m) together with very low resistivity values (70 Ω × μm) and capacitances in the attofarad range. These results are particularly relevant for further optimization of the nanowire-FET terahertz detectors recently demonstrated
InAs nanowire superconducting tunnel junctions: spectroscopy, thermometry and nanorefrigeration
We demonstrate an original method -- based on controlled oxidation -- to
create high-quality tunnel junctions between superconducting Al reservoirs and
InAs semiconductor nanowires. We show clean tunnel characteristics with a
current suppression by over orders of magnitude for a junction bias well
below the Al gap . The experimental data
are in close agreement with the BCS theoretical expectations of a
superconducting tunnel junction. The studied devices combine small-scale tunnel
contacts working as thermometers as well as larger electrodes that provide a
proof-of-principle active {\em cooling} of the electron distribution in the
nanowire. A peak refrigeration of about is achieved
at a bath temperature in our prototype
devices. This method opens important perspectives for the investigation of
thermoelectric effects in semiconductor nanostructures and for nanoscale
refrigeration.Comment: 6 pages, 4 color figure
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