370 research outputs found
X-ray mapping in a scanning transmission electron microscope of InGaAs quantum dots with embedded fractional monolayers of aluminium
We investigate AlGaAs/GaAs superlattices as well as InGaAs/GaAs quantum wells (QWs) and epitaxial quantum dots (QDs) where during the molecular beam epitaxy of InGaAs QDs the aluminium flux cell was opened briefly to incorporate fractional monolayers of Al into the InGaAs. We show that X-ray mapping with a large collection angle is capable to detect 0.3-0.4 fractional Al monolayers with a resolution of just under 1nm
Carrier and Light Trapping in Graded Quantum Well Laser Structures
We investigated the carrier and light trapping in GaInAs/AlGaAs single
quantum well laser structures by means of time resolved photoluminescence and
Raman spectroscopy. The influence of the shape and depth of the confinement
potential and of the cavity geometry was studied by using different AlGaAs/GaAs
short-period superlattices as barriers. Our results show that grading the
optical cavity improves considerably both carrier and light trapping in the
quantum well, and that the trapping efficiency is enhanced by increasing the
graded confining potential.Comment: PDF-format, 15 pages (including 4 figures), Applied Physics Letters
(June 2000
Exciton lifetime and emission polarization dispersion in strongly in-plane asymmetric nanostructures
We present experimental and theoretical investigation of exciton
recombination dynamics and the related polarization of emission in highly
in-plane asymmetric nanostructures. Considering general asymmetry- and
size-driven effects, we illustrate them with a detailed analysis of
InAs/AlGaInAs/InP elongated quantum dots. These offer a widely varied
confinement characteristics tuned by size and geometry that are tailored during
the growth process, which leads to emission in the application-relevant
spectral range of 1.25-1.65 {\mu}m. By exploring the interplay of the very
shallow hole confining potential and widely varying structural asymmetry, we
show that a transition from the strong through intermediate to even weak
confinement regime is possible in nanostructures of this kind. This has a
significant impact on exciton recombination dynamics and the polarization of
emission, which are shown to depend not only on details of the calculated
excitonic states but also on excitation conditions in the photoluminescence
experiments. We estimate the impact of the latter and propose a way to
determine the intrinsic polarization-dependent exciton light-matter coupling
based on kinetic characteristics.Comment: 11 pages, 8 figure
Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant
We present the first experimental evidence for the existence of strongly
localized photonic modes due to random two dimensional fluctuations in the
dielectric constant. In one direction, the modes are trapped by ordered Bragg
reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity
plane, they are localized by disorder, which is due to randomness in the
position, composition and sizes of quantum dots located in the anti-node of the
cavity. We extend the theory of disorder induced strong localization of
electron states to optical modes and obtain quantitative agreement with the
main experimental observations.Comment: 6 page
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