47 research outputs found
Spectral broadening in self-assembled GaAs quantum dots with narrow size distribution
The control over the spectral broadening of an ensemble of emitters, mainly
attributable to the size and shape dispersion and the homogenous broadening
mechanisms, is crucial to several applications of quantum dots. We present a
convenient self-assembly approach to deliver strain-free GaAs quantum dots with
size distribution below 15%, due to the control of the growth parameters during
the preliminary formation of the Ga droplets. This results in an ensemble
photoluminescence linewidth of 19 meV at 14 K. The narrow emission band and the
absence of a wetting layer promoting dot-dot coupling allow us to deconvolve
the contribution of phonon broadening in the ensemble photoluminescence and
study it in a wide temperature range.Comment: 9 pages, 4 figure
Complex Nanostructures by Pulsed Droplet Epitaxy
What makes three dimensional semiconductor
quantum nanostructures so attractive is the possibility to
tune their electronic properties by careful design of their
size and composition. These parameters set the
confinement potential of electrons and holes, thus
determining the electronic and optical properties of the
nanostructure. An often overlooked parameter, which has
an even more relevant effect on the electronic properties
of the nanostructure, is shape. Gaining a strong control
over the electronic properties via shape tuning is the key
to access subtle electronic design possibilities. The Pulsed
Dropled Epitaxy is an innovative growth method for the
fabrication of quantum nanostructures with highly
designable shapes and complex morphologies. With
Pulsed Dropled Epitaxy it is possible to combine different
nanostructures, namely quantum dots, quantum rings
and quantum disks, with tunable sizes and densities, into
a single multi‐function nanostructure, thus allowing an
unprecedented control over electronic properties
High-yield fabrication of entangled photon emitters for hybrid quantum networking using high-temperature droplet epitaxy
Several semiconductor quantum dot techniques have been investigated for the
generation of entangled photon pairs. Among the other techniques, droplet
epitaxy enables the control of the shape, size, density, and emission
wavelength of the quantum emitters. However, the fraction of the
entanglement-ready quantum dots that can be fabricated with this method is
still limited to around 5%, and matching the energy of the entangled photons to
atomic transitions (a promising route towards quantum networking) remains an
outstanding challenge.
Here, we overcome these obstacles by introducing a modified approach to
droplet epitaxy on a high symmetry (111)A substrate, where the fundamental
crystallization step is performed at a significantly higher temperature as
compared to previous reports. Our method drastically improves the yield of
entanglement-ready photon sources near the emission wavelength of interest,
which can be as high as 95% due to the low values of fine structure splitting
and radiative lifetime, together with the reduced exciton dephasing offered by
the choice of GaAs/AlGaAs materials. The quantum dots are designed to emit in
the operating spectral region of Rb-based slow-light media, providing a viable
technology for quantum repeater stations.Comment: 14 pages, 3 figure
High-temperature droplet epitaxy of symmetric GaAs/AlGaAs quantum dots
We introduce a high-temperature droplet epitaxy procedure, based on the
control of the arsenization dynamics of nanoscale droplets of liquid Ga on
GaAs(111)A surfaces. The use of high temperatures for the self-assembly of
droplet epitaxy quantum dots solves major issues related to material defects,
introduced during the droplet epitaxy fabrication process, which limited its
use for single and entangled photon sources for quantum photonics applications.
We identify the region in the parameter space which allows quantum dots to
self-assemble with the desired emission wavelength and highly symmetric shape
while maintaining a high optical quality. The role of the growth parameters
during the droplet arsenization is discussed and modelled.Comment: 18 pages, 5 figure
Optically controlled dual-band quantum dot infrared photodetector
We present the design for a novel type of dual-band photodetector in the
thermal infrared spectral range, the Optically Controlled Dual-band quantum dot
Infrared Photodetector (OCDIP). This concept is based on a quantum dot ensemble
with a unimodal size distribution, whose absorption spectrum can be controlled
by optically-injected carriers. An external pumping laser varies the electron
density in the QDs, permitting to control the available electronic transitions
and thus the absorption spectrum. We grew a test sample which we studied by AFM
and photoluminescence. Based on the experimental data, we simulated the
infrared absorption spectrum of the sample, which showed two absorption bands
at 5.85 um and 8.98 um depending on the excitation power
Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization
Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent “ballistic” behavior of lattice vibrations, the phonons. If dominant, such behavior would determine the mechanism for transport and relaxation in various energy-conversion applications. In order to study this coherent limit, both the spatial and temporal resolutions must be sufficient for the length-time scales involved. Here, we report observation of the lattice dynamics in nanoscale quantum dots of gallium arsenide using ultrafast electron diffraction. By varying the dot size from h = 11 to 46 nm, the length scale effect was examined, together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the atomic-scale resolution and a sufficiently high time resolution, other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization
Complex Nanostructures by Pulsed Droplet Epitaxy
What makes three dimensional semiconductor
quantum nanostructures so attractive is the possibility to
tune their electronic properties by careful design of their
size and composition. These parameters set the
confinement potential of electrons and holes, thus
determining the electronic and optical properties of the
nanostructure. An often overlooked parameter, which has
an even more relevant effect on the electronic properties
of the nanostructure, is shape. Gaining a strong control
over the electronic properties via shape tuning is the key
to access subtle electronic design possibilities. The Pulsed
Dropled Epitaxy is an innovative growth method for the
fabrication of quantum nanostructures with highly
designable shapes and complex morphologies. With
Pulsed Dropled Epitaxy it is possible to combine different
nanostructures, namely quantum dots, quantum rings
and quantum disks, with tunable sizes and densities, into
a single multi‐function nanostructure, thus allowing an
unprecedented control over electronic properties