Critical thickness in epitaxial CdTe/ZnTe

Cibert, J.; Gobil, Y.; Dang, Le Si; Tatarenko, S.; Feuillet, G.; Jouneau, P. H.; Saminadayar, K.

doi:10.1063/1.102812

Cited by 93 publications

(26 citation statements)

References 10 publications

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“…As the growth proceeds (h increases), the initial 2D-coherent growth mode changes into the 2D-MD one when the layer thickness h exceeds a critical value h c MD of about 5 monolayers (MLs). This is confirmed by the observation in situ of a streaky RHEED pattern as previously reported for CdTe/ZnTe (see for example Cibert et al [8]). Note that this behavior contrasts with the one predicted [17] and observed [18] for InAs/GaAs (001): in this case the transition which occurs first is the elastic one with the formation of coherent islands at a critical thickness h c SK of about 1.7 ML.…”

supporting

confidence: 89%

“…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.…”

mentioning

confidence: 61%

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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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supporting

confidence: 89%

mentioning

confidence: 61%

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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“…Lattice constants of free-standing wurtzite InAs and InP are a͑InAs͒ = 0.42 nm, c͑InAs͒ = 0.69 nm and a͑InP͒ = 0.40 nm, c͑InP͒ = 0.66 nm, respectively. Thickness of the InAs hexagonal tube, a few MLs, is less than the critical thickness for the onset of strain relaxation 11 and therefore the ultrathin InAs hexagonal tube is considered to be coherently strained in all directions and to be in nearly hydrostatic strain field. Model-solid theory by Van de Walle 12 explains that nearly hydrostatic strain field forms type-II band lineup.…”

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confidence: 99%

One- and two-dimensional spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires

et al. 2010

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Spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires ͑CMNs͒ and type-I excitons in an InAs/InP single quantum well ͑SQW͒ was studied by means of time-resolved and spectrally resolved photoluminescence. InP/InAs/InP CMNs in hexagonal symmetry are made of six facets and six edges which work as two-dimensional quantum wells and one-dimensional quantum wires, respectively. At 5 K type-II excitons lose their energy in two stages. In the first stage, two-dimensional spectral diffusion takes place in the type-II quantum well region in CMNs similar to spectral diffusion of type-I excitons in the InAs/InP SQW. In the second stage, slower one-dimensional spectral diffusion takes place in the quantum wire region in CMNs. Acoustic-phonon-mediated migration of excitons to lower-energy-localized states leads to the spectral diffusion in two dimensions and one dimension. Carrier localization in the disordered system depends highly on dimensionality and size. A sharp mobility edge is present for transport in three dimensions while is absent in two dimensions.1 Optical spectroscopy has revealed inhomogeneous broadening of excitons, exciton localization, exciton mobility edge, and exciton spectral diffusion in the disordered system. In fact, spectral diffusion of excitons is widely observed in inhomogeneously broadened exciton bands of quasi-two-dimensional quantum wells ͑QWs͒ ͑Refs. 2-4͒ and three-dimensional mixed crystals. 5,6 Exciton localization, delocalization, and mobility edge are reported in quasitwo-dimensional QW.7 Usually observed features are ͑1͒ photoluminescence ͑PL͒ decay becomes gradually slower with decrease in the photon energy and ͑2͒ time-resolved PL spectrum is gradually shifted toward lower energy as time proceeds. Spectral diffusion is believed to take place by the acoustic-phonon-mediated spatial transfer of excitons localized in the fluctuated potential.It is expected that spectral diffusion highly depends on the dimensionality. In three dimensions, spatial transfer of excitons localized in the fluctuated potential is not difficult, because localized excitons can find the nearby sites with very small energy mismatch. On the other hand, in one dimension, it is difficult because of the limited path for the spatial transfer. Dimensionality-dependent spectral diffusion is predicted theoretically 8 but has not been studied experimentally. Quantum structures having both two-dimensional QWs and onedimensional quantum wires ͑QWRs͒ are idealistic system for the study of the dimensionality-dependent spectral diffusion. In this work, we study type-II exciton dynamics in wurtzite InP/InAs/InP core-multishell nanowires ͑CMNs͒ composed of two-dimensional QWs and one-dimensional QWRs and type-I exciton dynamics in an InAs/InP single QW ͑SQW͒ by using time-resolved and spectrally resolved PL. It is also needed to understand the similarity or difference in the spectral diffusion of type-I excitons and type-II excitons. The scope of the study is to observe two-dimensional and onedimensional spe...

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“…First, a thick ZnTe or Zn 0.7 Mg 0.3 Te buffer layer is grown at 360°C on a (001)-ZnTe substrate. Secondly, a highly strained two-dimensional CdTe layer is grown at 300°C at a thickness just below the onset of plastic relaxation: 4.2 and 7.2 ML on ZnTe [9] and on Zn 0.7 Mg 0.3 Te, respectively. At this stage of the growth the RHEED pattern is still streaky.…”

Section: Growth and Experimentsmentioning

confidence: 99%

Influence of Mg on the temperature‐dependent optical properties of CdTe quantum dots embedded in Zn _0.7 Mg _0.3 Te

Tinjod¹,

Moehl²,

Kheng³

et al. 2004

phys. stat. sol. (c)

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We compare the temperature-dependent optical properties of CdTe quantum dots with and without Mg in their Zn(Mg)Te barriers. The difficulty of forming CdTe dots on Zn 0.7 Mg 0.3 Te barriers (due to the decrease of the lattice mismatch) has been overcome by using a new technique based on an efficient reduction of the surface energy. Mg incorporation in the barriers leads to a better heavy-hole confinement along the growth axis, which is manifested in PL studies by both an extension of the radiative regime temperature range and a strong increase of the activation energy for the non-radiative mechanisms. However, the in-plane confinement is less enhanced, which leads to progressive inter-dot carrier transfers with increasing temperature, as evidenced directly by the analysis of photoluminescence intensities for different single dots. Our temperature-dependent data (time-resolved and micro-photoluminescence) indicate that this transfer consists of a thermally activated process via the two-dimensional wetting-layer states.1 Introduction In recent years much attention has been paid to the fabrication of semiconductor quantum dots (QDs) and to their specific optical properties. In particular, optical studies at low temperatures (typically below few tens of Kelvins) provide very interesting information on the basic physics of confined excitons. They also show the potential of quantum dots as active media for opto-electronic devices such as, for instance, single photon emitters. However, to go further, one has to demonstrate the feasibility of such devices at higher temperature. For this purpose, it is important (i) to use materials that have a large exciton binding energy, and (ii) to understand and control the mechanisms responsible for the thermal escape of excitons from 0D confined states towards non-radiative channels.The strong Coulomb interaction in II-VI QDs as compared to most III-Vs (except GaN dots) makes them very attractive for single photon generation as demonstrated recently at intermediate temperature with CdSe QDs [1]. For CdTe/ZnTe QDs however, emission at room temperature has not yet been observed, neither for an ensemble of QDs [2,3], nor for a spatially selected individual dot [4]. This can be attributed to the very small unstrained valence band offset (VBO) of the CdTe/ZnTe system [5,6].This limitation may be overcome however, by incorporating Mg into ZnTe barriers. Calculations have predicted a VBO of 63% for ZnTe/MgTe [6] (because of the lack of Mg d-orbitals) and VBOs as large as 30% and 87% have been found experimentally for telluride (CdTe/CdMgTe QW) [7] and selenide (ZnSe/ZnMgSe QW) [8] systems, respectively. Thus, incorporating Mg into ZnTe barriers is expected to increase the potential confinement for the heavy hole, and so to significantly strengthen the excitonic emission.In this paper, we compare the temperature-dependent optical properties of CdTe self-assembled quantum dots embedded in either pure ZnTe or Zn 0.7 Mg 0.3 Te barriers and we show the improvement brought

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Critical thickness in epitaxial CdTe/ZnTe

Cited by 93 publications

References 10 publications

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

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

One- and two-dimensional spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires

Influence of Mg on the temperature‐dependent optical properties of CdTe quantum dots embedded in Zn _0.7 Mg _0.3 Te

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Critical thickness in epitaxial CdTe/ZnTe

Cited by 93 publications

References 10 publications

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

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

One- and two-dimensional spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires

Influence of Mg on the temperature‐dependent optical properties of CdTe quantum dots embedded in Zn 0.7 Mg 0.3 Te

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Influence of Mg on the temperature‐dependent optical properties of CdTe quantum dots embedded in Zn _0.7 Mg _0.3 Te