Lateral redistribution of excitons in CdSe/ZnSe quantum dots

Straßburg, M.; Dworzak, M.; Born, H.; Heitz, R.; Hoffmann, A.; Bartels, M.; Lischka, K.; Schikora, D.; Christen, J.

doi:10.1063/1.1432743

Cited by 54 publications

(39 citation statements)

References 16 publications

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“…By raising temperature the energy position of E ME decreases faster than the maximum of the PL band (E PL ), which follows the Varshni law (with parameters a = 5.405 Â 10 À4 eV/K, b = 204). Signs of the red shift of the mobility edge when temperature increases (but similar to the band gap shift) has been also observed recently by other authors in CdSe/ZnSe nanostructures [4]. The inset shows the almost lineal variation of E ME À E PL when temperature increases.…”

Section: Samples and Experimentssupporting

confidence: 55%

Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells

Rudamas

Martínez‐Pastor

González³

et al. 2003

phys. stat. sol. (c)

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Continuous wave and time-resolved photoluminescence studies as a function of temperature have been performed on disordered In x Ga 1Àx P/GaAs quantum wells. Simulations of stationary and transient spectra, by using a two-exciton kinetic model, allow the observation of a red shift of the effective mobility edge when temperature increases. From the temperature dependence of the radiative lifetime it can be also deduced that independent localization of electrons and holes seems to be the most likely mechanism for exciton localization in our samples. On the other hand, values ranging from 0.8 to 5.6 ps have been obtained for the radiative lifetime at k k = 0. . The co-existence of localized and free excitons reflected in the two-class exciton kinetic model presented in a previous work [3] seems to describe the experimental results obtained by continuous-wave-(PL) and time-resolved-photoluminescence (TRPL) measurements as a function of temperature in In x Ga 1Àx P/GaAs quantum wells. An effective mobility edge (E ME ) defined by a Fermi function was introduced in that model. In this paper, we present an study of the variation of E ME when temperature increases and, by considering two limiting cases, we try to make a deeper view inside of the exciton in-plane localization nature.

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Section: Samples and Experimentssupporting

confidence: 55%

Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells

Rudamas

Martínez‐Pastor

González³

et al. 2003

phys. stat. sol. (c)

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“…For quantum dot systems a rate equation approach has been used [6]. In these systems, the shift has been interpreted in terms of an inter-island relaxation [7]. Interpretation of optical spectra has, however, indicated the fractal nature of the island shape [8,9].…”

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Temperature dependent excitonic relaxation in CdSe/ZnSe quantum islands: experiment and computer simulation

Don

Koháry

Tsitsischvili

et al. 2003

phys. stat. sol. (c)

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In this contribution, a Monte-Carlo computer simulation of phonon-assisted relaxation processes of excitons in CdSe/ZnSe quantum islands is presented. With the same set of parameters, it was possible to reproduce both the temperature dependence of the energy position and of the full width at half maximum (FWHM) of the luminescence emitted from a ZnCdSe quantum film containing 5 to 10 nm wide Cd-rich islands. With help of the model, the energy dependence of the distribution of the localized states is shown to be weaker than Gaussian. Furthermore, the obtained fitting parameters give evidence for an intra-island excitonic relaxation. Finally, our results, based on a realistic description of the exciton kinetics, are compared with those of a rate equation model. 1 Introduction In localized systems, and among them in quantum-dot systems, thermally activated excitons can transfer to adjacent states with the help of phonon-assisted processes. As a result, the energy position of the photoluminescence (PL) maximum exhibits a "red-blue-red"-shift with increasing temperature [1]. This anormalous shift is well known for various quantum-well systems, where it was observed experimentally [2-4] and described theoretically [5]. For quantum dot systems a rate equation approach has been used [6]. In these systems, the shift has been interpreted in terms of an inter-island relaxation [7]. Interpretation of optical spectra has, however, indicated the fractal nature of the island shape [8,9]. In the resulting potential, intra-island hopping relaxation of excitons would be possible.In this paper, the scenario of an intra-island spatial relaxation is tested. Experimental results for the anomalous PL shift are compared with a Monte-Carlo simulation of phonon-assisted hopping [10]. After a description of the sample and of the experimental data, the operating principle of the simulation and its application to our experimental data are presented. Then the obtained parameter sets and their meaning for the distribution of localization centers for hopping processes will be discussed. Finally, the model is compared with the results of a calculation based on rate equations.

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“…SK grown islands lead to a pronounced redshift of the emission wavelength with increasing temperature. As it was shown by temperature dependent and time delayed photoluminescence (PL) spectroscopy [3,4], this redshift is caused by a lateral redistribution of excitons to deeper localisation sites.…”

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Analysis of Quantum Dot Formation and Exciton Localisation in the (Zn, Cd) (S, Se) System

Straßburg

Christen

Dworzak

et al. 2002

phys. stat. sol. (b)

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The formation process and exciton localisation properties of CdSe/ZnSe quantum dot structures were studied. Pseudomorphically strained structures were exposed to a stationary sulphur vapour after the formation process of three-dimensional (3D) islands. Temperature dependent photoluminescence investigations confirm the increasing 2D-like character with increasing sulphur exposure times. The sulphur exposure had no impact on the island formation in partially relaxed structures.Introduction The growth of self-assembled quantum dots (QDs) using molecular beam epitaxy (MBE) or metal-organic chemical vapour deposition (MOCVD) is of considerable interest as it offers the possibility for low-threshold-current opto-electronic devices for the green spectral range. Furthermore, such structures have the potential to study basic phenomena of quantum information processing. However, reliable data necessary for a controlled formation of well ordered arrays of CdSe QDs are difficult to obtain and not fully available presently.As reported earlier [1], two distinctly different types of CdSe islands are formed in succession during the deposition of about 3 monolayers (ML) CdSe on ZnSe (001). From kinetic analysis we have concluded that above a critical threshold of about 2.1 ML the islands are formed by the Stranski-Krastanov (SK) growth process, which is thermodynamically controlled. To proof that, in this paper, we demonstrate for the first time the reversible nature of this particular growth mode transition. A similar approach has been reported earlier for the behaviour of InAs islands on GaAs [2]. The presence of deep localisation sites as provided by e.g. SK grown islands lead to a pronounced redshift of the emission wavelength with increasing temperature. As it was shown by temperature dependent and time delayed photoluminescence (PL) spectroscopy [3,4], this redshift is caused by a lateral redistribution of excitons to deeper localisation sites.

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Lateral redistribution of excitons in CdSe/ZnSe quantum dots

Cited by 54 publications

References 16 publications

Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells

Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells

Temperature dependent excitonic relaxation in CdSe/ZnSe quantum islands: experiment and computer simulation

Analysis of Quantum Dot Formation and Exciton Localisation in the (Zn, Cd) (S, Se) System

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Lateral redistribution of excitons in CdSe/ZnSe quantum dots

Cited by 54 publications

References 16 publications

Exciton kinetics and luminescence in disordered In x Ga 1− x P/GaAs quantum wells

Exciton kinetics and luminescence in disordered In x Ga 1− x P/GaAs quantum wells

Temperature dependent excitonic relaxation in CdSe/ZnSe quantum islands: experiment and computer simulation

Analysis of Quantum Dot Formation and Exciton Localisation in the (Zn, Cd) (S, Se) System

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Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells

Exciton kinetics and luminescence in disordered In _x Ga _{1−
x} P/GaAs quantum wells