79 research outputs found
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
Carrier trapping and luminescence polarization in quantum dashes
We study experimentally and theoretically polarization-dependent luminescence
from an ensemble of quantum-dot-like nanostructures with a very large in-plane
shape anisotropy (quantum dashes). We show that the measured degree of linear
polarization of the emitted light increases with the excitation power and
changes with temperature in a non-trivial way, depending on the excitation
conditions. Using an approximate model based on the k.p theory, we are able to
relate this degree of polarization to the amount of light hole admixture in the
exciton states which, in turn, depends on the symmetry of the envelope wave
function. Agreement between the measured properties and theory is reached under
assumption that the ground exciton state in a quantum dash is trapped in a
confinement fluctuation within the structure and thus localized in a much
smaller volume of much lower asymmetry than the entire nanostructure.Comment: 13 pages, 9 figures; considerably extended, additional discussion and
new figures include
Single-photon emission of InAs/InP quantum dashes at 1.55 μm and temperatures up to 80 K
This research was supported by the National Science Center of Poland within Grant No. 2011/02/A/ST3/00152.We report on single photon emission from a self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 µm at elevated temperatures. The photon auto-correlation histograms of the emission from a charged exciton indicate clear antibunching dips with as-measured g(2)(0) values significantly below 0.5 recorded at temperatures up to 80 K. It proves that charged exciton complex in a single quantum dash of the mature InP-based material system can act as a true single photon source up to at least liquid nitrogen temperature. This demonstrates the huge potential of InAs on InP nanostructures as non-classical light emitters for long-distance fiber-based secure communication technologies.PostprintPublisher PDFPeer reviewe
Monolayered MoSe2: a candidate for room temperature polaritonics
We acknowledge financial support by the state of Bavaria. EC, AK and SH acknowledge the EPSRC Programme "Hybrid Polaritonics" (EP/M025330/1) for support. ST acknowledges support from NSF DMR-1552220. CS acknowledges support by the European Research Council within the project UnLiMIt-2D (grant number 679288).Monolayered MoSe2 is a promising new material to investigate advanced light-matter coupling as it hosts stable and robust excitons with comparably narrow optical resonances. In this work, we investigate the evolution of the lowest lying excitonic transition, the so-called A-valley exciton, with temperature. We find a strong, phonon-induced temperature broadening of the resonance, and more importantly, a reduction of the oscillator strength for increased temperatures, which we describe in the framework of a microscopic model. Based on these experimentally extracted, temperature dependent parameters, we apply a coupled oscillator model to elucidate the possibility to observe the strong coupling regime between the A-exciton and a microcavity resonance in three prototypical photonic architectures with varying mode volumes. We find that the formation of exciton-polaritons up to ambient conditions in compact, monolithic dielectric and Tamm-based structures seems feasible. In contrast, a temperature-induced transition into the weak coupling regime can be expected for structures with extended effective cavity length. Based on these findings, we calculate and draw the phase diagram of polariton Bosonic condensation in a microcavity with embedded MoSe2 monolayers.PostprintPeer reviewe
Excitonic fine structure and binding energies of excitonic complexes in single InAs quantum dashes
P.M., J.M. and G. S. acknowledge support from the grant of National Science Centre of Poland No. 2011/02/A/ST3/00152 (Maestro), whereas M.Z. acknowledges support from the Polish National Science Centre under grant No. 2015/18/E/ST3/005 (Sonata Bis). The experiments have partially been performed within the Wroclaw University of Science and Technology laboratory infrastructure financed by the Polish Ministry of Science and Higher Education Grant No. 6167/IA/119/2012.The fundamental electronic and optical properties of elongated InAs nanostructures embedded in quaternary InGaAlAs barrier are investigated by means of high-resolution optical spectroscopy and many-body atomistic tight-binding theory. These wire-like shaped self-assembled nanostructures are known as quantum dashes and are typically formed during the molecular beam epitaxial growth on InP substrates. In this work we study properties of excitonic complexes confined in quantum dashes emitting in a broad spectral range from below 1.2 to 1.55 μm. We find peculiar trends for the biexciton and negative trion binding energies, with pronounced trion binding in smaller size quantum dashes. These experimental findings are then compared and qualitatively explained by atomistic theory. The theoretical analysis shows a fundamental role of correlation effects for the absolute values of excitonic binding energies. Eventually, we determine the bright exciton fine structure splitting (FSS), where both the experiment and theory predict a broad distribution of the splitting varying from below 50 to almost 180 μeV. We identify several key factors determining the FSS values in such nanostructures including quantum dash size variation and composition fluctuations.PostprintPeer reviewe
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