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

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

Carrier delocalization in InAs/InGaAlAs/InP quantum‐dash‐based tunnel injection system for 1.55 μm emission

The work has been supported by the grant No. 2013/10/M/ST3/00636 of the National Science Centre in Poland and the QuCoS Project of Deutsche Forschungsgemeinschaft No. RE1110/16‐1.We have investigated optical properties of hybrid two‐dimensional‐zero‐dimensional (2D‐0D) tunnel structures containing strongly elongated InAs/InP(001) quantum dots (called quantum dashes), emitting at 1.55 μm. These quantum dashes (QDashes) are separated by a 2.3 nm‐width barrier from an InGaAs quantum well (QW), lattice matched to InP. We have tailored quantum‐mechanical coupling between the states confined in QDashes and a QW by changing the QW thickness. By combining modulation spectroscopy and photoluminescence excitation, we have determined the energies of all relevant optical transitions in the system and proven the carrier transfer from the QW to the QDashes, which is the fundamental requirement for the tunnel injection scheme. A transformation between 0D and mixed‐type 2D‐0D character of an electron and a hole confinement in the ground state of the hybrid system have been probed by time‐resolved photoluminescence that revealed considerable changes in PL decay time with the QW width changes. The experimental discoveries have been explained by band structure calculations in the framework of the eight‐band k⋅p model showing that they are driven by delocalization of the lowest energy hole state. The hole delocalization process from the 0D QDash confinement is unfavorable for optical devices based on such tunnel injection structures.Publisher PDFPeer reviewe

Exciton lifetime and emission polarization dispersion in strongly in-plane asymmetric nanostructures

The work was supported by the Grant No. 2011/02/A/ST3/00152 from the Polish National Science Centre (Narodowe Centrum Nauki). K. G. acknowledges support by the Grant No. 2014/12/B/ST3/04603 from the Polish National Science Centre (Narodowe Centrum Nauki). S. H. acknowledges support from the State of Bavaria in Germany.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 μm. 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.PostprintPeer reviewe

Magnetic field control of the neutral and charged exciton fine structure in single quantum dashes emitting at 1.55 μ m

This research was supported by the Polish Ministry of Science and Higher Education/the National Science Center Grant No. 2011/02/A/ST3/00152. S.H. gratefully acknowledges support by the Royal Society and the Wolfson Foundation.We investigated the neutral and charged exciton fine structure in single InAs/InGaAlAs/InP quantum dashes emitting at 1.55 μm using polarization-resolved microphotoluminescence in a magnetic field. Inverted spin configuration of horizontally [1-10] and vertically [110] polarized transitions has been observed. An in-plane magnetic field of up to 5 Tesla has been applied to tailor the fine structure, and eventually to reduce the splitting of the bright exciton states down to zero. This inverted structure has been observed for all the investigated excitons, making it a characteristic feature for this class of nanostructures with the largest splitting reduction of 170 μeV.Publisher PDFPeer reviewe

Single photon emission up to liquid nitrogen temperature from charged excitons confined in GaAs-based epitaxial nanostructures

We demonstrate a non-classical photon emitter at near infrared wavelength based on a single (In,Ga)As/GaAs epitaxially grown columnar quantum dot. Charged exciton complexes have been identified in magneto-photoluminescence. Photon auto-correlation histograms from the recombination of a trion confined in a columnar dot exhibit sub-Poissonian statistics with an antibunching dip yielding g(2)(0) values of 0.28 and 0.46 at temperature of 10 and 80 K, respectively. Our experimental findings allow considering the GaAs-based columnar quantum dot structure as an efficient single photon source operating at above liquid nitrogen temperatures, which in some characteristics can outperform the existing solutions of any material system

Optimizing the InGaAs/GaAs quantum dots for 1.3 μm emission

Hereby we present comprehensive experimental and theoretical study on fundamental optical properties and electronic structure of GaAs-based quantum dots grown using metalorganic chemical vapor deposition technique. The substantial redshift of emission, to the second telecommunication window of 1.3 μm, in comparison to standard InGaAs/GaAs quantum dots is obtained via strain engineering utilizing additional capping layer of In_{0.2}Ga_{0.8}As in this context referred to as strain reducing layer. It ensures lowering of the energy of the ground state transition to more application relevant spectral range. Optical properties of the quantum dot structure has been experimentally characterized by means of photoreflectance spectroscopy and power-dependent photoluminescence revealing 3 transitions originating from hybrid states confined in an asymmetric double quantum well formed of the wetting layer and strain reducing layer, as well as higher states of the quantum dots themselves with the first excited state transition separated by 67 meV from the ground state transition. Origin of the observed transitions was confirmed in theoretical modelling using 1-band single-particle approach for the quantum well part, and excitonic quantum dot spectrum obtained within 8 band k·p formalism followed by configuration interaction calculations, respectively. Additionally, photoluminescence excitation spectroscopy measurements allowed to identify a spectral range for efficient quasi-resonant excitation of the investigated quantum dots into the 2D density of states to be in the range of 835-905 nm