5 research outputs found
Supplementary document for Wide angle anapole excitation in stacked resonators - 6615750.pdf
Figure S1 and S
Diameter-Dependent Photocurrent in InAsSb Nanowire Infrared Photodetectors
Photoconductors using vertical arrays
of InAs/InAs<sub>1ā<i>x</i></sub>Sb<sub><i>x</i></sub> nanowires with varying
Sb composition <i>x</i> have been fabricated and characterized.
The spectrally resolved photocurrents are strongly diameter dependent
with peaks, which are red-shifted with diameter, appearing for thicker
wires. Results from numerical simulations are in good agreement with
the experimental data and reveal that the peaks are due to resonant
modes that enhance the coupling of light into the wires. Through proper
selection of wire diameter, the absorptance can be increased by more
than 1 order of magnitude at a specific wavelength compared to a thin
planar film with the same amount of material. A maximum 20% cutoff
wavelength of 5.7 Ī¼m is obtained at 5 K for a wire diameter
of 717 nm at a Sb content of <i>x</i> = 0.62, but simulations
predict that detection at longer wavelengths can be achieved by increasing
the diameter. Furthermore, photodetection in InAsSb nanowire arrays
integrated on Si substrates is also demonstrated
Colorful InAs Nanowire Arrays: From Strong to Weak Absorption with Geometrical Tuning
One-dimensional nanostructure arrays can show fascinatingly
different,
tunable optical response compared to bulk systems. Here we study theoretically
and demonstrate experimentally how to engineer the reflection and
absorption of light in epitaxially grown vertical arrays of InAs nanowires
(NWs). A striking observation is optically visible colors of the array,
which we show can be tuned depending on the geometrical parameters
of the array. Specifically, larger diameter NW arrays absorb light
more effectively out to a longer wavelength compared to smaller diameter
arrays. Thus, controlling the diameter provides a way to tune the
optically observable color of an array. We also find that arrays with
a larger amount of InAs material reflect less light (or absorb more
light) than arrays with less material. On the basis of these two trends,
InAs NW arrays can be designed to absorb light either much more or
much less efficiently than a thin film of an effective medium containing
the same amount of InAs as the NW array. The tunable absorption and
low area filling factor of the NW arrays compared to thin film bode
well for III-V photovoltaics and photodetection
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
Bipolar Photothermoelectric Effect Across Energy Filters in Single Nanowires
The
photothermoelectric (PTE) effect uses nonuniform absorption of light
to produce a voltage via the Seebeck effect and is of interest for
optical sensing and solar-to-electric energy conversion. However,
the utility of PTE devices reported to date has been limited by the
need to use a tightly focused laser spot to achieve the required,
nonuniform illumination and by their dependence upon the Seebeck coefficients
of the constituent materials, which exhibit limited tunability and,
generally, low values. Here, we use InAs/InP heterostructure nanowires
to overcome these limitations: first, we use naturally occurring absorption
āhot
spotsā at wave mode maxima within the nanowire to achieve sharp
boundaries between heated and unheated subwavelength regions of high
and low absorption, allowing us to use global illumination; second,
we employ carrier energy-filtering heterostructures to achieve a high
Seebeck coefficient that is tunable by heterostructure design. Using
these methods, we demonstrate PTE voltages of hundreds of millivolts
at room temperature from a globally illuminated nanowire device. Furthermore,
we find PTE currents and voltages that change polarity as a function
of the wavelength of illumination due to spatial shifting of subwavelength
absorption hot spots. These results indicate the feasibility of designing
new types of PTE-based photodetectors, photothermoelectrics, and hot-carrier
solar cells using nanowires