The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots (original) (raw)
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Quadexciton cascade and fine-structure splitting of the triexciton in a single quantum dot
EPL (Europhysics Letters), 2016
We report the properties of emission lines associated with the cascaded recombination of a quadexciton in single GaAlAs/AlAs quantum dots, studied by means of polarization-resolved photoluminescence and single-photon correlation experiments. It is found that photons which are emitted in a double-step 4X-3X process preserve their linear polarization, similarly to the case of conserved polarization of correlated photons in the 2X-X cascade. In contrast, an emission of either co-linear or cross-linear pairs of photons is observed for the 3X-2X cascade. Each emission line associated with the quadexciton cascade shows doublet structure in the polarization-resolved photoluminescence experiment. The maximum splitting is seen when the polarization axis is chosen along and perpendicular to the [110] crystallographic direction. This effect is ascribed to the fine structure splitting of the exciton and triexciton states in the presence of an anisotropic confining potential of ae dot. We also show that the splitting in the triexciton state surpasses that in the exciton state by a factor up to eight and their ratio scales with the energy distance between the 3X and X emission lines, thus, very likely, with a lateral size and/or a composition of the dot.
Internal electronic structure and fine structure of multiexcitons in semiconductor quantum dots
Physical Review B, 2009
We perform a detailed theoretical study of the characteristic internal electronic structure of various multiexcitons ͑N h , N e ͒, where N h is number of holes and N e is the number of electrons in the self-assembled semiconductor quantum dots ͑QDs͒. For each of the leading ͑N h , N e ͒ excitonic complexes we start from the single-particle configuration ͑e.g., a specific occupation pattern of S and P electron and hole levels by a few carriers͒ and then show the many-particle multiplet levels for the initial state of emission ͑N h , N e ͒ and the final state of emission ͑N h −1, N e −1͒. We denote which states are dark and which are bright; the order and multiplicity, the leading single-particle character of each multiplet state, and the fine-structure splittings. These are of general utility. We also show explicit numerical values for distances between various transitions for four specific QDs. Here the presented information is important and potentially useful for a few reasons: ͑i͒ the information serves as a guide for spectroscopic interpretation; ͑ii͒ the information reveals non-Aufbau cases, where the dot does not have Aufbau occupation of carriers' levels; ͑iii͒ the information shows which transitions are sensitive to random-alloy fluctuations ͑if the dot is alloyed͒ and importance of this effect. We show that because of such alloy information, distances between peaks cannot be used to gauge structural information.
Multiexcitonic emission from single elongated InGaAs/GaAs quantum dots
Journal of Applied Physics, 2012
In this work we present both experiments and simulations of multiexcitonic emission spectra of single self-assembled elongated In 0.3 Ga 0.7 As/GaAs quantum dots. The emission spectra reveal an unusual evolution with the increased excitation power density. First, a biexciton line appears simultaneously with its low energy sideband, origin of which has already been postulated previously and related to interaction of quantum dot biexciton with excitons generated in the surrounding wetting layer. A further increase of the excitation causes a disappearance of the exciton line accompanied with a transformation of the biexciton sharp line and its side band into a redshifting broad emission band. The latter recalls a typical feature of the transition from excitonic emission into electron-hole plasma called Mott transition, which is possible to occur in wire-like structures under the conditions of very high carrier densities. However, we propose an alternative explanation and show that this behavior can be well explained based on a multilevel rate equation model indicating that such a dependence of the emission spectra is a fingerprint of a formation of multiexcitonic states. Further, we discuss the importance of various quantum system parameters as the radiative lifetimes or spectral linewidths.
Single-exciton energy shell structure in InAs/GaAs quantum dots
Physical Review B, 2008
The energy shell structure of a single exciton confined in a self-assembled quantum dot ͑QD͒, including excited states, is studied in a regime where the direct Coulomb attraction energy is comparable to the kinetic energy of the carriers. This is achieved via magnetophotoluminescence excitation spectroscopy experiments, where a magnetic field applied perpendicular to the plane of the QD is used to reveal the angular-momentum content of energy shells. The absorption spectrum of the QDs is modeled, and comparison with experiment allows us to relate the observed transitions to interband QD bound-state transitions. The blueshift of the absorption peaks compared to the emission peaks is then interpreted in terms of many-body interactions, and we show that for a highly symmetric situation, the observed energy difference gives a direct measurement of the extra exchange energy gained upon addition of an extra exciton in the QD.
Physical Review Letters, 2005
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wavefunctions through asymmetric e-e and e-h exchange interactions.
Observation of multicharged excitons and biexcitons in a single InGaAs quantum dot
Physical Review B, 2001
The effects of excess electron occupation on the optical properties of excitons ͑X͒ and biexcitons (2X) in a single self-assembled InGaAs quantum dot are investigated. The behavior of X and 2X differ strongly as the number of excess electrons is varied with the biexciton being much more weakly perturbed as a result of its filled s-shell ground state, a direct manifestation of shell-filling effects. Good correlation is found between charging thresholds observed from s-shell recombination perturbed by p-shell occupation, and direct observation of p-shell recombination.
Polarization properties of excitonic qubits in single self-assembled quantum dots
Physical Review B, 2012
We investigate polarization properties of neutral exciton emission in single self-assembled InAs/GaAs quantum dots. The in-plane shape and strain anisotropy strongly couple the heavy and light hole states and lead to large optical anisotropy with non-orthogonal linearly polarized states misaligned with respect to the crystallographic axes. Owing to a waveguiding experimental configuration, luminescence polarization along the growth axis has been observed revealing the presence of shear components of the deformation tensor out of the growth plane. Resonant luminescence experiments allowed determining the oscillator strength ratio of the two exciton eigenstates. Valence band mixing governs this ratio and can be very different from dot to dot, however the polarization anisotropy axis is quite fixed inside a scanned area of one µm 2 and indicates that the in-plane deformation direction to which it is related has a correlation length of the order of magnitude of one µm 2 .
2007
We present photoluminescence studies of the molecular neutral biexciton-exciton spectra of individual vertically stacked InAs= GaAs quantum dot pairs. We tune either the hole or the electron levels of the two dots into tunneling resonances. The spectra are described well within a few-level, few-particle molecular model. Their properties can be modified broadly by an electric field and by structural design, which makes them highly attractive for controlling nonlinear optical properties.