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Oueslati, M.; Zouaghi, M.K.; Pistol, Mats Erik; Samuelson, Lars; Grimmeiss, H. G.; Bałkanski, M.

doi:10.1103/physrevb.32.8220

Cited by 82 publications

(18 citation statements)

References 11 publications

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“…The transition between the two drift processes (localized to delocalized states) is referred in the literature as the mobility edge. 19,20 In conclusion, we compute by means of MC simulations the speed of bound excitons in an energy gradient. We show that the mean speed of excitons is strongly dependent to temperature and Bohr radius.…”

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confidence: 99%

Hopping process of bound excitons under an energy gradient

Jacopin

Shahmohammadi

Ganière

et al. 2014

Applied Physics Letters

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We report on the mechanism of hopping for bound excitons under an energy gradient. By means of a Monte-Carlo simulation, we show that this mechanism explains the movement of bound excitons observed experimentally. We show that the speed of the excitons decreases quickly with temperature. Thanks to an effective medium approximation, we deduce an analytical model to estimate the average speed at T ¼ 0 K. Finally, we compare our simulations results to the speed observed in bent ZnO wires and find a good agreement between theory and experiments. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4863319] The ability to tune the strain in different structures is interesting for many applications such as the enhancement of the mobility in transistors 1 or the engineering of the optical polarization properties of heterostructures.2,3 Recently, it has been shown that it is possible to design nano/microstructures to obtain a strain gradient and control the motion of excitons. 4,5 In particular, bent nanowires have gained considerable attention because of the possibility to tune the bandgap without plastic relaxation.6-8 For instance, it has been recently demonstrated that excitons can move because of the strain gradient induced by the bending of a wire. However, at T ¼ 10 K at which the experiments are performed, the photoluminescence of ZnO wires is dominated by the emission coming from the donor bound exciton (D X). Thus, experimental evidence indicates that donor bound excitons are drifted by the strain gradient, against simple views implied by their name: "donor bound exciton."The motion of bound excitons has already been observed in inhomogeneous materials such as GaAsP:N, 10,11 InGaN, 12 and MgZnO alloys. 13 In these random alloys, the transfer of such excitons from one donor to another is driven by the tunneling of exciton to lower states. The same mechanism has been observed and successfully described by a stochastic model of exciton transfer in homogeneous GaP with well-defined impurities levels.14 However, in such samples, the random distribution of lowest states makes it difficult to obtain an accurate estimation of the characteristic time for the exciton to jump from one donor to the other.The strain-induced energy gradient in bent micro/nanowires directly builds a "donor ladder" as observed in the scheme of Figure 1. Indeed, because of the continuous change of bandgap energy, the relative positions of donors are sorted by energy along the strain gradient. This arrangement of donors gives the possibility to get an accurate estimation of the hopping rate of excitons, unlike in the case of inhomogeneous materials.In this Letter, we propose a model for the hopping process of donor bound excitons in the presence of an energy gradient. We compute the exciton dynamics by means of Monte-Carlo (MC) simulations taking into account the probability for the transfer of an exciton from a donor to another. We compare the case of zero temperature to the case of a nonzero temperature and show that the mean speed shoul...

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confidence: 99%

Hopping process of bound excitons under an energy gradient

Jacopin

Shahmohammadi

Ganière

et al. 2014

Applied Physics Letters

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“…[21,22] The observation of DALA modes in In x Al 1−x As layers is allowed owing to the breakdown of the wave-vector conservation law induced by the disorder. [23] This also means that phonons with nonzero qvectors which are activated by the disorder contribute to the scattering process. [22,24] From Fig.…”

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confidence: 99%

Raman study of V/III flux ratio effect in InP/InAlAs/InP heterostructures grown by MOCVD

Sayari¹,

Yahyaoui²,

Oueslati³

et al. 2009

J Raman Spectroscopy

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Micro-Raman measurements have been carried out in order to study the V/III flux ratio effect in InP/InAlAs/InP heterostructures grown by metal-organic chemical vapor deposition (MOCVD). Photoluminescence (PL) studies in InP/InAlAs/InP heterostructures [1,2] show a strong dependence of the PL band linewidth on V/III molar ratio. In addition to the observation of the two-mode behavior and the disorder activated modes in InAlAs alloy, an analysis of Raman spectra shows a line shape broadening and wavenumber shift of Raman peaks for various V/III molar ratios, with minimum linewidth and lattice mismatch occurring at V/III = 50. Also, a strong dependence on the composition modulation of the AlAs-like longitudinal optic (LO AlAs−like ) phonon was observed due to clustering. Calculation of the in-plane strain shows that the lattice mismatch between the epilayer and the substrate is relatively insensitive to flux ratio variation within the range investigated. Therefore, the high arsenic overpressures used have an insignificant adverse effect on the quality of the hetero-interfaces.

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“…At low temperatures we observe two discrete thermal activation energies of 5 meV and 17 meV at T < 30 K and T < 120 K, respectively. This thermally activated behaviour provides additional evidence of effect of localized excitons [11]. The activation energy of 79 meV at high temperatures may be associated with thermionic emission of holes from the well.…”

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confidence: 93%

Time‐resolved photoluminescence and steady‐state optical studies of GaInNAs and GaInAs single quantum wells

Sun

Lombez

Braun

et al. 2007

Phys. Status Solidi (c)

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Time-resolved photoluminescence spectroscopy is used to investigate carrier dynamics of Ga 1-x In x N y As 1-y (x ~ 0.33, y ~ 0.01) single quantum well (QW) structures. PL spectra measured as a function of temperature together with the PL decay times at wavelengths around and below the PL peak energy are used to determine de-trapping activation energies and time constants. The results are interpreted in terms of simultaneous thermal excitation of deep localized excitons to shallow localized states. According to the model, with increasing temperatures, localized excitons gain enough thermal energy to populate the free exciton states in quantum well with shorter lifetimes due to coherent nature of free excitons. In addition, at temperatures around and above 80 K, more non-radiative channels become available to compete with the radiative processes leading to shorter time constants. 1 Introduction Dilute nitride alloys (GaAsN, InGaAsN and GaAsSbN) have recently attracted considerable attention as promising materials for long wavelength laser diodes as well as high efficient multijunction solar cells. The incorporation of a low content of nitrogen (< 2%) in the host material induces dramatic changes in the optical and electronic properties [1][2][3]. However, the compositional nonuniformity of nitrogen and indium induces a spatial distribution of different sized clusters hence to the associated states [4,5]. These cluster states reflect potential fluctuations that are inherent in the disordered systems resulting in the creation of intrinsic regions of strong localization. Strongly localized states dominate radiative recombination dynamics at low temperatures. In this contribution, we report on the time resolved photoluminescence (TRPL) studies of sequentially grown GaInNAs/GaAs and GaInAs/GaAs single quantum wells. We interpret our results in terms of localized excitons in nitrogen containing quantum well but free exciton recombination in nitrogen free well.

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Photoluminescence study of localization effects induced by the fluctuating random alloy potential in indirect band-gapGaAs1−x

Cited by 82 publications

References 11 publications

Hopping process of bound excitons under an energy gradient

Hopping process of bound excitons under an energy gradient

Raman study of V/III flux ratio effect in InP/InAlAs/InP heterostructures grown by MOCVD

Time‐resolved photoluminescence and steady‐state optical studies of GaInNAs and GaInAs single quantum wells

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