217 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
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
Dynamics of mass transport during nanohole drilling by local droplet etching
Local droplet etching (LDE) utilizes metal droplets during molecular beam epitaxy for the self-assembled drilling of nanoholes into III/V semiconductor surfaces. An essential process during LDE is the removal of the deposited droplet material from its initial position during post-growth annealing. This paper studies the droplet material removal experimentally and discusses the results in terms of a simple model. The first set of experiments demonstrates that the droplet material is removed by detachment of atoms and spreading over the substrate surface. Further experiments establish that droplet etching requires a small arsenic background pressure to inhibit re-attachment of the detached atoms. Surfaces processed under completely minimized As pressure show no hole formation but instead a conservation of the initial droplets. Under consideration of these results, a simple kinetic scaling model of the etching process is proposed that quantitatively reproduces experimental data on the hole depth as a function of the process temperature and deposited amount of droplet material. Furthermore, the depth dependence of the hole side-facet angle is analyzed
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
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