Self-organized In͑Ga͒As/GaAs quantum dots ͑QDs͒ grown on ͑111͒ substrate are proposed as ideal sources for the generation of entangled photon pairs. Due to the threefold rotational symmetry of the ͑111͒ surface, QDs with C 3v symmetry or higher are expected to develop during growth. In contrast to QDs on ͑001͒-oriented substrates, the symmetry of the confinement potential of ͑111͒ QDs is not lowered by piezoelectric effects. As a result the excitonic bright splitting vanishes and the biexciton→ exciton→ 0 recombination cascade can be used for the generation of entangled photons. We evaluate the spectroscopic separability of excitonic and biexcitonic emissions as a function of QD size, shape, and composition using the configuration-interaction model in conjunction with eight-band k · p theory. The piezoelectric field in ͑111͒ QDs predominantly aligns along the growth direction and gives rise to vertical charge separation. First-and second-order piezoelectric fields are oriented in opposite directions. The In/Ga ratio inside the QD determines the leading contribution and can be employed to balance both terms in order to achieve a field-free situation with maximal electron-hole overlap. The biexciton binding energy depends on the net piezoelectric potential drop across the QD vertical extension and becomes maximal if the first-and second-order fields outweigh each other within the QD interior.
Coupling of acoustic and optical phonons to excitons in single InGaAs/GaAs quantum dots is investigated in detail experimentally and theoretically as a function of temperature. For the theoretical description of the luminescence spectrum, including acoustic and optical phonon scattering, we used the exactly solvable independent boson model. Surprisingly, only GaAs bulk-type longitudinal-optical (LO) phonons are detected in experiment. A quantitatively correct theoretical description of the optical-phonon replica is obtained by including a limited lifetime of the phonons and the dispersion of the LO phonon energy. Similarly, a numerically correct description of the acoustic phonon wings is again based on GaAs bulk material parameters for the phonon dispersion and deformation coupling. In addition, the line shape of the calculated spectra agrees with experiment only when realistic wave functions (e.g., based on eight-band k•p theory) are used for the electron-phonon coupling matrix elements. Gaussian wave functions describing the ground state of a harmonic oscillator fail to describe high-energy tails. Thus, fundamental insights of importance for the correct prediction of properties of nonclassical light sources, based on semiconductor nanostructures, are obtained.
In this letter, we demonstrate that self-organized InGaAs quantum dots ͑QDs͒ grown on GaAs ͑111͒ substrate using droplet epitaxy have great potential for the generation of entangled photon pairs. The QDs show spectrally sharp luminescence lines and low spatial density. A second order correlation value of g ͑2͒ ͑0͒ Ͻ 0.3 proves single-photon emission. By comparing the power dependence of the luminescence from a number of QDs we identify a typical luminescence fingerprint. In polarization dependent microphotoluminescence studies a fine-structure splitting ranging Յ40 eV down to the determination limit of our setup ͑10 eV͒ was observed.
The efficient generation of polarized single or entangled photons is a crucial requirement for the implementation of quantum key distribution (QKD) systems. Selforganized semiconductor quantum dots (QDs) are capable of emitting one polarized photon or an entangled photon pair at a time using appropriate electrical current injection. We realized a highly efficient single-photon source (SPS) based on well-established semiconductor technology: In a pin structure, a single electron and a single hole are funneled into a single InAs QD using a submicron AlO x current aperture. Efficient radiative recombination leads to emission of single polarized photons with an all-time record purity of the spectrum. Non-classicality of the emitted light without using additional spectral filtering is demonstrated. The out-coupling efficiency and the emission rate are increased by embedding the SPS into a micro-cavity. The design of the micro-cavity is based on detailed modeling to optimize its performance. The resulting resonant single-QD diode is driven at a repetition rate of 1 GHz, exhibiting a second-order correlation function of g ð2Þ ð0Þ ¼ 0. Eventually, QDs grown on (111)-oriented substrates are proposed as a source of entangled photon pairs. Intrinsic symmetry-lowering effects leading to the splitting of the exciton bright states are shown to be absent for this substrate orientation. As a result, the XX ! X ! 0 recombination cascade of a QD can be used for the generation of entangled photons without further tuning of the fine-structure splitting via QD size and/or shape.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.