Internal electric field in wurtzite<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Zn</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mo>∕</mml:mo><mml:msub><mml:mi mathvariant="normal">Zn</mml:mi><mml:mn>0.78</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">Mg</mml:mi><mml:mn>0.22</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>quantum wells

Morhain, C.; Bretagnon, Thierry; Lefèbvre, Pierre; Tang, Xiaodong; Valvin, Pierre; Guillet, Thierry; Gil, Bernard; Taliercio, Thierry; Teisseire-Doninelli, M.; Vinter, B.; Deparis, C.

doi:10.1103/physrevb.72.241305

Cited by 212 publications

(149 citation statements)

References 31 publications

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“…For relatively wide QWs, with widths larger than 3 nm, the exciton transition energies are lower than those of the ZnO bulk and decrease linearly with the well width while at the same time the lifetime increases exponentially. In order to determine the internal electric field from the experimental results, we have calculated the energy of the fundamental transition, the binding energy, and the oscillator strength of the ground-state exciton by a variational method [30,31] that includes the electric field. The numerical parameters used in the calculation are m e = 0.24 and m h = 0.78 for electron and hole on-axis effective masses and ε b = 6.4 for the dielectric constant, in both well and barrier materials.…”

Section: Energy (Ev) Intens Ty (Arb Un Ts)mentioning

confidence: 99%

Optical properties of ZnO/(Zn, Mg)O quantum wells

Bretagnon

2014

Turk J Phys

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This paper reviews the optical properties of ZnO/(Zn, Mg)O single quantum wells grown by molecular beam epitaxy. Both heteroepitaxial quantum well growth along the polar c-direction and homoepitaxial quantum well growth on the nonpolar M plane cases are considered. The optical properties of these quantum wells are investigated by using reflectance, continuous wave photoluminescence, and time-resolved photoluminescence spectroscopies. The quantum-confined Stark effect dominates the properties of the excitons for polar quantum wells. The magnitude of the internal electric field that is induced by both spontaneous and piezoelectric polarizations is determined by comparing the experimental results with a variational calculation of excitonic energies and lifetimes. For nonpolar quantum wells, the optical spectra reveal strong in-plane optical anisotropies, as predicted by the group theory. Moreover, the radiative recombination of free excitons is dominating the quantum well photoluminescence even at room temperature.

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Section: Energy (Ev) Intens Ty (Arb Un Ts)mentioning

confidence: 99%

Optical properties of ZnO/(Zn, Mg)O quantum wells

Bretagnon

2014

Turk J Phys

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“…1a. The charges on the interfaces between ZnO and MgZnO result in a built-in electric field in the structure, which is stronger for polar samples [4,23]. The built-in electric field pulls the electron and the hole toward opposite borders of the QW, resulting in the spatial separation required for an IX.…”

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confidence: 99%

“…IXs were realized in wide single quantum wells (WSQW) [1][2][3][4] and in coupled quantum wells (CQW) [5][6][7][8] [2-4, 6, 7]. Their long lifetimes allow IXs to travel over large distances before recombination, providing the opportunity to study exciton transport by optical imaging [9][10][11][12][13][14][15] and explore excitonic circuit devices based on exciton transport, see [16] and references therein.…”

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confidence: 99%

Transport of indirect excitons in ZnO quantum wells

et al. 2015

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We report on spatially-and time-resolved emission measurements and observation of transport of indirect excitons in ZnO/MgZnO wide single quantum wells.An indirect exciton (IX) in a semiconductor quantum well (QW) structure is composed of an electron and a hole confined to spatially separated QW layers. IXs were realized in wide single quantum wells (WSQW) [1][2][3][4] and in coupled quantum wells (CQW) [5][6][7][8] [2-4, 6, 7]. Their long lifetimes allow IXs to travel over large distances before recombination, providing the opportunity to study exciton transport by optical imaging [9][10][11][12][13][14][15] and explore excitonic circuit devices based on exciton transport, see [16] and references therein.Materials with a high IX binding energy allow extending the operation of the excitonic devices to high temperatures [17][18][19]. Furthermore, such materials can allow the realization of high-temperature coherent states of IXs [19]. These properties make materials with robust IXs particularly interesting. However, so far, studies of IX transport mainly concerned GaAs-based CQW. In this paper, we probe transport of IXs in ZnO/MgZnO WSQW structures. IXs in these structures are much more robust than in GaAs structures: their binding energy ∼ 30 meV [4] is considerably higher than that in GaAs/AlGaAs and GaAs/AlAs CQW (∼ 4 and ∼ 10 meV, respectively [7,20]). The binding energy of IXs is smaller than that of excitons in bulk ZnO (∼ 60 meV), however it is large enough to make the IXs stable at room temperature. At the same time, the measurements reported in this work show that transport lengths of IXs in WSQW ZnO structures reach ∼ 4 µm. In comparison, for excitons in bulk ZnO and direct excitons in ZnO structures, transport lengths are within ∼ 0.2 µm [21,22].In this work, we study polar and semipolar ZnO/MgZnO QW structures. The samples were grown by molecular beam epitaxy as in Refs. [4,23] Fig. 1a. The charges on the interfaces between ZnO and MgZnO result in a built-in electric field in the structure, which is stronger for polar samples [4,23]. The built-in electric field pulls the electron and the hole toward opposite borders of the QW, resulting in the spatial separation required for an IX.

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“…The carrier separation is achieved through the use of type II heterojunctions [1,2], or through the introduction of internal electric fields via doping or compositional gradients. In the case of polar materials, such as wurtzite III-nitride or II-oxide semiconductors [3,4], internal electric fields appear spontaneously in heterostructures due to the polarization difference between binary compounds [5]. In particular, adding up spontaneous and piezoelectric polarization, AlN/GaN quantum wells present an internal electric field on the order of 10 MV/cm [6], which leads to efficient electron-hole separation along the polar 0001 axis, and considerably increases the band-to-band radiative recombination time [7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Long-lived excitons in GaN/AlN nanowire heterostructures

et al. 2015

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GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts.

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Internal electric field in wurtziteZnO∕Zn0.78Mg0.22Oquantum wells

Cited by 212 publications

References 31 publications

Optical properties of ZnO/(Zn, Mg)O quantum wells

Optical properties of ZnO/(Zn, Mg)O quantum wells

Transport of indirect excitons in ZnO quantum wells

Long-lived excitons in GaN/AlN nanowire heterostructures

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