12 research outputs found
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 2Ć10Ā¹āø to 1Ć10Ā¹ā¹ācmĀÆĀ³, while the surface charge density exceeds 5Ć10Ā¹Ā²ācmĀÆĀ² 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
In<sub><i>x</i></sub>Ga<sub>1ā<i>x</i></sub>P Nanowire Growth Dynamics Strongly Affected by Doping Using Diethylzinc
Semiconductor
nanowires are versatile building blocks for optoelectronic devices,
in part because nanowires offer an increased freedom in material design
due to relaxed constraints on lattice matching during the epitaxial
growth. This enables the growth of ternary alloy nanowires in which
the bandgap is tunable over a large energy range, desirable for optoelectronic
devices. However, little is known about the effects of doping in the
ternary nanowire materials, a prerequisite for applications. Here
we present a study of p-doping of In<sub><i>x</i></sub>Ga<sub>1ā<i>x</i></sub>P nanowires and show that the growth
dynamics are strongly affected when diethylzinc is used as a dopant
precursor. Specifically, using in situ optical reflectometry and high-resolution
transmission electron microscopy we show that the doping results in
a smaller nanowire diameter, a more predominant zincblende crystal
structure, a more Ga-rich composition, and an increased axial growth
rate. We attribute these effects to changes in seed particle wetting
angle and increased TMGa pyrolysis efficiency upon introducing diethylzinc.
Lastly, we demonstrate degenerate p-doping levels in In<sub><i>x</i></sub>Ga<sub>1ā<i>x</i></sub>P nanowires
by the realization of an Esaki tunnel diode. Our findings provide
insights into the growth dynamics of ternary alloy nanowires during
doping, thus potentially enabling the realization of such nanowires
with high compositional homogeneity and controlled doping for high-performance
optoelectronics devices
Gate-Induced Fermi Level Tuning in InP Nanowires at Efficiency Close to the Thermal Limit
Tunnel Field-Effect Transistors Based on InP-GaAs Heterostructure Nanowires
We present tunneling field-effect transistors fabricated from InP-GaAs heterostructure nanowires with an <i>n-i-p</i> doping profile, where the intrinsic InP region is modulated by a top gate. The devices show an inverse subthreshold slope down to 50 mV/dec averaged over two decades with an on/off current ratio of approximately 10<sup>7</sup> for a gate voltage swing (<i>V</i><sub>GS</sub>) of 1 V and an on-current of 2.2 Ī¼A/Ī¼m. Low-temperature measurements suggest a mechanism of trap-assisted tunneling, possibly explained by a narrow band gap segment of InGaAsP
Optical Far-Field Method with Subwavelength Accuracy for the Determination of Nanostructure Dimensions in Large-Area Samples
The
physical, chemical, and biological properties of nanostructures
depend strongly on their geometrical dimensions. Here we present a
fast, noninvasive, simple-to-perform, purely optical method that is
capable of characterizing nanostructure dimensions over large areas
with an accuracy comparable to that of scanning electron microscopy.
This far-field method is based on the analysis of unique fingerprints
in experimentally measured reflectance spectra using full three-dimensional
optical modeling. We demonstrate the strength of our method on large-area
(millimeter-sized) arrays of vertical InP nanowires, for which we
simultaneously determine the diameter and length as well as cross-sample
morphological variations thereof. Explicitly, the diameter is determined
with an accuracy better than 10 nm and the length with an accuracy
better than 30 nm. The method is versatile and robust, and we believe
that it will provide a powerful and standardized measurement technique
for large-area nanostructure arrays suitable for both research and
industrial applications
Electron Trapping in InP Nanowire FETs with Stacking Faults
Semiconductor IIIāV nanowires are promising components of
future electronic and optoelectronic devices, but they typically show
a mixed wurtzite-zinc blende crystal structure. Here we show, theoretically
and experimentally, that the crystal structure dominates the conductivity
in such InP nanowires. Undoped devices show very low conductivities
and mobilities. The zincblende segments are quantum wells orthogonal
to the current path and our calculations indicate that an electron
concentration of up to 4.6 Ć 10<sup>18</sup> cm<sup>ā3</sup> can be trapped in these. The calculations also show that the room
temperature conductivity is controlled by the longest zincblende segment,
and that stochastic variations in this length lead to an order of
magnitude variation in conductivity. The mobility shows an unexpected
decrease for low doping levels, as well as an unusual temperature
dependence that bear resemblance with polycrystalline semiconductors
Structural Properties of Wurtzite InPāInGaAs Nanowire CoreāShell Heterostructures
We report on growth and characterization
of wurtzite InPāIn<sub>1ā<i>x</i></sub>Ga<sub><i>x</i></sub>As
coreāshell nanowire heterostructures. A range of nanowire structures
with different Ga concentration in the shell was characterized with
transmission electron microscopy and X-ray diffraction. We found that
the main part of the nanowires has a pure wurtzite crystal structure,
with occasional stacking faults occurring only at the top and bottom.
This allowed us to determine the structural properties of wurtzite
In<sub>1ā<i>x</i></sub>Ga<sub><i>x</i></sub>As. The InPāIn<sub>1ā<i>x</i></sub>Ga<sub><i>x</i></sub>As coreāshell nanowires show a triangular
and hexagonal facet structure of {1100} and {101Ģ
0} planes.
X-ray diffraction measurements showed that the core and the shell
are pseudomorphic along the <i>c</i>-axis, and the strained
axial lattice constant is closer to the relaxed In<sub>1ā<i>x</i></sub>Ga<sub><i>x</i></sub>As shell. Microphotoluminescence
measurements of the nanowires show emission in the infrared regime,
which makes them suitable for applications in optical communication
Carrier Recombination Processes in Gallium Indium Phosphide Nanowires
Understanding
of recombination and photoconductivity dynamics of photogenerated
charge carriers in Ga<sub><i>x</i></sub>In<sub>1āx</sub>P NWs is essential for their optoelectronic applications. In this
letter, we have studied a series of Ga<sub><i>x</i></sub>In<sub>1āx</sub>P NWs with varied Ga composition. Time-resolved
photoinduced luminescence, femtosecond transient absorption, and time-resolved
THz transmission measurements were performed to assess radiative and
nonradiative recombination and photoconductivity dynamics of photogenerated
charges in the NWs. We conclude that radiative recombination dynamics
is limited by hole trapping, whereas electrons are highly mobile until
they recombine nonradiatively. We also resolve gradual decrease of
mobility of photogenerated electrons assigned to electron trapping
and detrapping in a distribution of trap states. We identify that
the nonradiative recombination of charges is much slower than the
decay of the photoluminescence signal. Further, we conclude that trapping
of both electrons and holes as well as nonradiative recombination
become faster with increasing Ga composition in Ga<sub><i>x</i></sub>In<sub>1āx</sub>P NWs. We have estimated early time
electron mobility in Ga<sub><i>x</i></sub>In<sub>1āx</sub>P NWs and found it to be strongly dependent on Ga composition due
to the contribution of electrons in the X-valley
Fluorescent Nanowire Heterostructures as a Versatile Tool for Biology Applications
Nanowires are increasingly used in
biology, as sensors, as injection
devices, and as model systems for toxicity studies. Currently, in
situ visualization of nanowires in biological media is done using
organic dyes, which are prone to photobleaching, or using microscopy
methods which either yield poor resolution or require a sophisticated
setup. Here we show that inherently fluorescent nanowire axial heterostructures
can be used to localize and identify nanowires in cells and tissue.
By synthesizing GaPāGaInP nanowire heterostructures, with nonfluorescent
GaP segments and fluorescent GaInP segments, we created a barcode
labeling system enabling the distinction of the nanowire morphological
and chemical properties using fluorescence microscopy. The GaInP photoluminescence
stability, combined with the fact that the nanowires can be coated
with different materials while retaining their fluorescence, make
these nanowires promising tools for biological and nanotoxicological
studies