Tuning the inter-shell splitting in self-assembled CdTe quantum dots

Kukliński, K.; Kłopotowski, Ł.; Fronc, K.; Wiater, M.; Wojnar, P.; Rutkowski, P.; Voliotis, Valia; Grousson, R.; Karczewski, G.; Kossut, J.; Wójtowicz, T.

doi:10.1063/1.3643476

Cited by 10 publications

(9 citation statements)

References 27 publications

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“…Most studies focus on the QD ground states in the prospect of several possible applications within the fields of quantum computing [1], advanced photon sources [2][3][4] and spintronics [5]. Less is known about the higher excited level structure, which is vital for the understanding of time-resolved phenomena like relaxation and dephasing mechanisms [6][7][8], recombinations of multiexcitons with more than two electrons or holes [9][10][11][12][13][14][15][16][17] or resonant absorption characteristics, typically measured via photoluminescence excitation (PLE) spectroscopy [6,[18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

2018

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Absorption spectra of neutral, negatively and positively charged semiconductor quantum dots are studied theoretically. We provide an overview of the main energetic structure around the pshell transitions, including the influence of nearby nominally dark states. Based on the envelope function approximation, we treat the four-band Luttinger theory as well as the direct and short range exchange Coulomb interactions within a configuration interaction approach. The quantum dot confinement is approximated by an anisotropic harmonic potential. We present a detailed investigation of state mixing and correlations mediated by the individual interactions. Differences and similarities between the differently charged quantum dots are highlighted. Especially large differences between negatively and positively charged quantum dots become evident. We present a visualisation of energetic shifts and state mixtures due to changes in size, in-plane asymmetry and aspect ratio. Thereby we provide a better understanding of the experimentally hard to access question of quantum dot geometry effects in general. Our findings show a new method to determine the in-plane asymmetry from photoluminescense excitation spectra. Furthermore, we supply basic knowledge for tailoring the strength of certain state mixtures or the energetic order of particular excited states via changes in the shape of the quantum dot, which is highly interesting e.g. to understand relaxation paths.

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Section: Introductionmentioning

confidence: 99%

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

2018

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“…We remark that CdTe QDs form a very inhomogeneous ensemble and therefore we cannot exclude a possibility of finding dots with a much stronger confinement, where both the transition sequence and recombinations rates would be different. We would expect such dots on the high energy side of the ensemble emission band and fabricated from a relatively wide CdTe layer, which was shown to decrease the lateral size [49]. For such dots, we would expect a transition sequence similar to the one reported for a majority of InGaAs dots, with the X + blueshifted with respect to the X 0 .…”

Section: Discussionmentioning

confidence: 64%

“…In the CdTe case however, the direction of the anisotropy varies from dot to dot and is not related to any crystallographic axes [47]. The energy levels of these dots exhibit an atomic-like shell structure as demonstrated by high excitation spectroscopy [49].…”

Section: Fabrication and Basic Properties Of Cdte Quantum Dotsmentioning

confidence: 94%

Charging Effects in Self-Assembled CdTe Quantum Dots

Kłopotowski

2011

Acta Phys. Pol. A

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In this review, we summarize our achievements in controlling and understanding the charging effects in single self-assembled CdTe quantum dots. We start with analysis of the single dot emission spectrum. For excitation densities small enough to ensure only s-shell recombination, we find that for all dots (also those reported by other groups) the same transition sequence is observed. Namely, the neutral exciton recombination has the highest energy while charged exciton and biexciton transitions are redshifted. This observation remains in a stark contrast to self-assembled InGaAs dots, where charged complexes may appear also on the high energy side of the neutral exciton. We explain the universality of the transition sequence assuming domination of the Coulomb correlations over direct, single particle interactions. Furthermore, through measurement of the recombination rates, we gain access to electron and hole wave functions and their redistributions upon changing the dot occupancy. We find that the electron wave function is rather stiff, while the hole wave function is rather soft owing to enhanced correlations in the valence band. We then corroborate these conclusions with the Stark spectroscopy, where we analyze energy shifts due to electric field imposed on dots embedded in a field effect or diode structure. Finally, we use these structures to obtain controllable tuning of the charge state. We discuss different approaches to this task and find the best tuning efficiency for a structure with enhanced valence band confinement.

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“…34 Moreover, the intershell splittings, proportional to the strength of the lateral confinement, increase with the number of CdTe monolayers from which the dots are formed and thus with the amount of accumulated strain. 35 In order to bring the carrier energies in adjacent QDs closer to resonance, we need to decrease the hole ionization energy in the top dot, e.g., by decreasing the amount of cadmium in the top dot with respect to the bottom one or by inducing a growth of a relatively smaller top QD. In the S1 samples, after the bottom layer of dots is formed, the subsequent barrier layer is subject to tensile strain as the ZnTe lattice atoms tend to align with the dangling bonds of the CdTe QD.…”

Section: Resultsmentioning

confidence: 99%

Engineering the hole confinement for CdTe-based quantum dot molecules

Kłopotowski

Wojnar

Kret

et al. 2015

Journal of Applied Physics

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We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum dots grown in a vertical stack. We achieve this by using materials with a different lattice constant for the growth of the outer and inner barriers. We monitor the resulting dot morphology with transmission electron microscopy studies and correlate the results with ensemble quantum dot photoluminescence. Furthermore, we embed the double quantum dots into diode structures and study photoluminescence as a function of bias voltage. We show that in properly engineered structures, it is possible to achieve a resonance of the hole states by tuning the energy levels with electric field. At the resonance, we observe signatures of a formation of a molecular state, hybridized over the two dots.

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Tuning the inter-shell splitting in self-assembled CdTe quantum dots

Cited by 10 publications

References 27 publications

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

Charging Effects in Self-Assembled CdTe Quantum Dots

Engineering the hole confinement for CdTe-based quantum dot molecules

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