Zero-dimensional excitons in CdTe/ZnTe nanostructures

Marsal, L.; Besombes, L.; Tinjod, F.; Kheng, K.; Wasiela, A.; Gilles, B.; Rouvière, J. L.; Mariette, H.

doi:10.1063/1.1436560

Cited by 61 publications

(46 citation statements)

References 46 publications

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“…While in the past most of these activities have been devoted to III-V compounds (see the Chapter by Petroff in this volume), Xin and coworkers demonstrated in 1996 for the first time the self-organized growth of CdSe/Zn(Mn)Se QDs [1]. Since this time, the epitaxial growth of II-VI QDs has been demonstrated for a variety of different systems, including CdSe/Zn(S)Se [2,3,4,5,6], CdSe/BeTe [7], Cd(Mn)Se/Zn(Mn)Se [8,9,10], CdTe/ZnTe [11] or CdSe/MgS [12]. Usually, these QDs are believed to consist of disc-shaped islands with diameters of 10 nm or below and heights of only a few nm.…”

Section: Introductionmentioning

confidence: 92%

Optical Spectroscopy on Epitaxially Grown II--VI Single Quantum Dots

Bacher

2003

Topics in Applied Physics

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Abstract. Spatially resolved optical spectroscopy applied to single non-magnetic and magnetic II-VI semiconductor quantum dots allows one to study optical, electronic and magnetic properties of single quantum objects. A controlled population of the quantum dot eigenstates by single particles can be obtained by laser excitation, in part combined with electrical current injection. This gives access to intrinsic properties of excitons and biexcitons, like phonon or exchange interaction or coupling to the radiation field. It is demonstrated that the eigenstates in single quantum dots can be manipulated in a well-controlled way simply by applying external electric and magnetic fields. This gives insight into the charge distribution and the g-factor of the particles within the dot. Introducing Mn 2+ ions into the crystal matrix results in an efficient spin-spin interaction between carriers and magnetic ions. We discuss giant magneto-optical effects like huge effective g-factors and the formation of quasi-zero-dimensional magnetic polarons and demonstrate how the optical response of a magnetic single quantum dot can be used to monitor nano-scale fluctuations of the magnetization.

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Section: Introductionmentioning

confidence: 92%

Optical Spectroscopy on Epitaxially Grown II--VI Single Quantum Dots

Bacher

2003

Topics in Applied Physics

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“…3,4,6,7,15 We studied several QDs in the depletion region of our device and surprisingly find that the polarization orientation with respect to the crystal axis is not identical for each QD, similar to that reported for CdTe/ ZnTe QDs. 17 Nevertheless, values for the FSS between 5 and 30 eV at zero applied bias were observed. Figure 5 displays the FSS for three QDs as a function of Stark shift.…”

Section: Figmentioning

confidence: 99%

Manipulating exciton fine structure in quantum dots with a lateral electric field

Gerardot

Seidl

Dalgarno

et al. 2007

Applied Physics Letters

211

165

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The fine structure of the neutral exciton in a single self-assembled InGaAs quantum dot is investigated under the effect of a lateral electric field. Stark shifts up to 1.5 meV, an increase in linewidth, and a decrease in photoluminescence intensity were observed due to the electric field. The authors show that the lateral electric field strongly affects the exciton fine-structure splitting due to active manipulation of the single particle wave functions. Remarkably, the splitting can be tuned over large values and through zero. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2431758͔There is currently great interest in producing entangled photons on demand for applications in quantum information processing. 1 One proposal which spurred much research is using radiative biexciton-exciton cascade in semiconductor quantum dots ͑QDs͒ to produce pairs of polarization entangled photons. 2 In an idealized QD, the bright exciton states ͑M = ±1͒ are degenerate. In this case the two decay paths from the biexciton to the vacuum state via the intermediate single exciton are indistinguishable in energy; thus photons emitted in the radiative cascade are polarization entangled. However, in practice, the rotational symmetry of a self-assembled QD is broken and the electron-hole exchange interaction mixes the bright exciton states into a nondegenerate doublet ͓referred to as a fine-structure splitting ͑FSS͔͒. This leads to an energetically distinguishable recombination path for the biexciton-exciton cascade. Polarization correlations are observed in the linear basis but polarization entanglement is destroyed due to the FSS. 3,4 For photons to be polarization entangled using this scheme, the requirement that the FSS be less than the homogeneous linewidth must be met. The FSS is typically 10-100 eV, while the homogeneous linewidth of self-assembled InGaAs QDs is ϳ1 eV. 5 Techniques used to actively tune the FSS include an inplane electric 6 or magnetic 7 field and an in situ uniaxial stress. 8 Also, QDs which are smaller due to the growth process 9 or subsequent annealing 10 have a smaller FSS. Unfortunately, such QDs are higher in energy and the QD photons become difficult to distinguish from those produced in the wetting layer. Recently, polarization entangled photons have been reported from specific QDs with energetically overlapping bright exciton states 11 and initially nondegenerate states tuned via a magnetic field. 12 However, a robust approach that would allow one to actively tune the FSS from a large value to zero for each QD is still necessary to realize an event ready entangled photon pair source. To this end we further explore the effect of a lateral electric field on the FSS.There are three basic characteristics of an exciton in a lateral electric field attributed to the quantum confined Stark effect, as has been investigated for quantum wells 13 and QDs: 14 a redshift in recombination energy, decreased oscillator strength, and an increase in nonradiative carrier tunneling probability. Additionally, electric fi...

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“…They are preferentially oriented along the [1 -1 0] axis as illustrated in the figure. This anisotropy accounts for the splitting of individual emission lines of capped QDs studied by linearly polarized micro-photoluminescence (µPL) [21] as also reported for InAs and CdSe QDs [25]. Note that the high-energy position of these lines (as compared to the energy gap of bulk CdTe) reveal some interdiffusion into the dots as already shown by high-resolution transmission electron microscopy studies [21,26].…”

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confidence: 72%

“…2b). ii) By using II-VIs' atomic layer epitaxy (ALE) [20,21]: ALE allows indeed to establish, after each flux sequence (successively Cd and then Te or Se), an equilibrium corresponding to a given surface reconstruction which minimizes the surface energy and so favors the SK transition as observed for CdTe by RHEED [22]. iii) Or by annealing for twenty minutes at 340°C under Se flux a CdSe layer, which also leads to a 3D RHEED pattern [23].…”

mentioning

confidence: 99%

Self‐assembled quantum dot formation induced by surface energy change of a strained two‐dimensional layer

Tinjod

Mariette

2004

Physica Status Solidi (b)

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To account for the occurrence (or not) of the Stranski-Krastanow (SK) transition (two-dimensional to 3D change of surface morphology) during the epitaxial growth of various lattice-mismatched semiconductor systems, we present a simple equilibrium model taking into account not only the lattice mismatch, but also the dislocation formation energy and the surface energy. It demonstrates the importance of these parameters especially for II-VI systems such as CdTe/ZnTe and CdSe/ZnSe. For II-VIs indeed, as misfit dislocations are easier to form than in III-Vs (such as InAs/GaAs) or IV systems (Ge/Si), the 3D elastic transition is short-circuited by the plastic one. Nevertheless, by lowering surface energy, telluride and selenide quantum dots can also be grown as predicted by our model and as evidenced experimentally by reflection high-energy electron diffraction (RHEED), atomic force microscopy and optical measurements.1 Introduction Some combinations of lattice-mismatched semiconductors can exhibit, under specific epitaxial growth conditions, a sharp transition from a layer-by-layer 2D growth to the formation of 3D islands. This Stranski-Krastanow (SK) growth mode [1] allows the relaxation of highly strained 2D layers trough the strain-free facets of 3D islands instead of generating misfit dislocations (MD) [2]. These islands are expected to be dislocation-free and are thus of high structural quality. Usually their typical sizes are on the scale of a few nanometers, so that these self-assembled quantum dots (QDs) are attractive nanostructures for the study of zero dimensional effects.The formation, above a critical film thickness, of such QDs by molecular beam epitaxy (MBE) is now well established for III-V semiconductors such as InAs/GaAs [3]. The large lattice mismatch (∆a/a ≈ 7%) between these two semiconductors is seen as the driving force which induces the 2D-3D change of the surface morphology with the formation of SK islands. However, in the case of II-VI systems, which can exhibit mismatch as large as 6% for CdTe/ZnTe or CdSe/ZnSe, the 2D-3D transition is much less obvious: no clear 3D RHEED pattern has been reported during growth although zero-dimensional behavior was obtained [4][5][6][7]. In II-VIs indeed, above critical thickness, MD form easier than in III-Vs as clearly observed for CdTe/ZnTe by Cibert et al. [8], which corresponds to a plastic relaxation as first considered by Frank and van der Merwe [2]. On the other hand, there are systems such as GaN/AlN [9] or SiGe/Si [10,11], with lower misfit (respectively 2.4% and less than 4%), which are known for exhibiting a clear SK transition with the formation of coherent islands.There are therefore other parameters than the lattice mismatch in order to account for the 2D-3D transition. In this paper a simple equilibrium model taking into account not only the lattice mismatch but also the dislocation formation energy and the surface energy, is presented to explain the occurrence (or not) of this 2D-3D transition for various semiconductor systems.

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Zero-dimensional excitons in CdTe/ZnTe nanostructures

Cited by 61 publications

References 46 publications

Optical Spectroscopy on Epitaxially Grown II--VI Single Quantum Dots

Optical Spectroscopy on Epitaxially Grown II--VI Single Quantum Dots

Manipulating exciton fine structure in quantum dots with a lateral electric field

Self‐assembled quantum dot formation induced by surface energy change of a strained two‐dimensional layer

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