Band alignment and excitonic localization of ZnO/Cd0.08Zn0.92O quantum wells

Matsui, Hiroaki; Osone, Takamasa; Tabata, Hitoshi

doi:10.1063/1.3359720

Cited by 13 publications

(10 citation statements)

References 28 publications

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“…However, for the thicker samples measurements were difficult due to the low PL intensity. Matsui et al also observed blue-shifts of the QW emission of up to 19 meV [5]. Though, they investigated samples with larger QW thicknesses in comparison to our samples in which the blue-shift is expected to be significantly larger -at least under the presence of the QCSE.…”

mentioning

confidence: 45%

“…Sadofev et al [2] have up to now exclusively proved the occurrence of the QCSE, by obtaining emission significantly below the respective thin film emission energies. Matsui et al concluded the occurrence of the QCSE as they obtain excitation-power dependent QW energies and a decrease of the degree of localization and the thermal activation energy of the PL-intensity quenching with increasing QW thickness [5]. However, they were not able to tune the emission energy significantly below that of the thin film.…”

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confidence: 99%

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Visible emission from ZnCdO/ZnO multiple quantum wells

Lange

Dietrich

Brachwitz

et al. 2011

Physica Rapid Research Ltrs

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Due to the large demand for optoelectronic devices covering the spectral range from green to ultraviolet, extensive research has been triggered into wide-bandgap group III-nitride semiconductors. Since InGaN-based devices exhibit a strong decrease in efficiency advancing the green spectral region [1], ZnO-based devices are a promising alternative.An emission energy in the visible spectral range was obtained in e.g. Zn 1-x Cd x O/ZnO quantum wells (QWs) or double heterostructures [2,3]. Large Cd contents up to ≈0.50 with emission energies down to 1.8 eV were obtained in wurtzite Zn 1-x Cd x O thin films [4], making a wide spectral range accessible. However, up to now only few publications exist that report on Zn 1-x Cd x O/ZnO QWs exhibiting emission energies far below theZnO bandgap resulting from difficulties to obtain large Cd contents in the QWs due to the low solubility of Cd in ZnO.For PLD-grown samples the lowest reported QW emission energy is as high as 2.76 eV. QW energies down to 2.2 eV are accessible for molecular beem epitaxy-grown samples, supported by the occurrence of the Quantum Confined Stark Effect (QCSE) [1], that is expected to occur in samples with a polar growth direction. Sadofev et al. [2] have up to now exclusively proved the occurrence of the QCSE, by obtaining emission significantly below the respective thin film emission energies. Matsui et al. concluded the occurrence of the QCSE as they obtain excitation-power dependent QW energies and a decrease of the degree of localization and the thermal activation energy of the PL-intensity quenching with increasing QW thickness [5]. However, they were not able to tune the emission energy significantly below that of the thin film. The absence of the QCSE in the other studies can be understood following the argumentation of Brandt et al. [6], who explained it for PLD-grown ZnO/Mg x Zn 1-x O QWs with reduced interface abruptness.In this Letter, optical properties of Zn 0.75 Cd 0.25 O/ZnO MQWs with small QW thicknesses are studied. They were deposited at low temperatures in order to achieve a high Cd content. MQWs were deposited to enhance the luminescence intensity and precisely determine the QW thickness by using X-ray diffraction (XRD). Due to the high Cd content, the MQW emission energy was tuned from 2.5 eV to 3.1 eV by varying the QW thickness.The MQW structures were grown on a-plane sapphire substrates using PLD. Sintered ceramic targets of highly Polar c-axis oriented Zn 0.75 Cd 0.25 O/ZnO multiple quantum wells (MQWs), grown by pulsed-laser deposition (PLD), emitting in the visible spectral range are reported. By applying a low growth temperature of ≈ 300 °C a large Cd content of 0.25 and abrupt interfaces could be achieved using PLD. The emission energy was tuned from the green to the violet spectral range (2.5 eV to 3.1 eV) by tuning the quantum well thickness. It is determined by the quantum confinement effect and the quantum-confined Stark effect.Intensity (arb. units) 2.0 2.5 3.0 Energy (eV) increasing well width

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confidence: 45%

mentioning

confidence: 99%

Visible emission from ZnCdO/ZnO multiple quantum wells

Lange

Dietrich

Brachwitz

et al. 2011

Physica Rapid Research Ltrs

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“…25) and quantum-confinement stark effect (QCSE) in ZnO quantum structures. 26,27 These phenomena are also related to the magnitude of the band-offset between well and barrier layers, which is related to band engineering. In contrast to Zn 1Àx Mg x O, it is further necessary to investigate the magnetic activity in Zn 1Àx Co x O while controlling the spontaneous polarization and band gap.…”

Section: Introductionmentioning

confidence: 99%

Lattice, band, and spin engineering in Zn1−xCoxO

Matsui

Tabata

2013

Journal of Applied Physics

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This work was conducted to investigate lattice, band, and spin engineering of magnetic Zn 1Àx Co x O layers towards quantum barriers in ZnO. Lattice distortions by doping with Co ions caused a flat tetrahedron in the host, leading to an increase of spontaneous polarization in Zn 1Àx Co x O compared to ZnO based on the point-charge model. The band-gap energy increased linearly with the Co concentrations, which was very similar to the band-gap widening in Zn 1Àx Mg x O derived from sp hybridization. The Co (3d) states were located in the mid-gap, which remained unchanged following changes in Co concentrations. Large magneto-optical effects were induced at the band edge due to sp-d exchange interactions. However, magneto-optical activity was reduced in heavily doping concentrations above x ¼ 0.16 because of antiferromagnetic coupling between nearest-neighbor Co ions. The high magnetic activity at x ¼ 0.10 is related to competition between the complex Co-related configurations, such as singles, pairs, open and closed triples, in Co-doped ZnO layers. Magnetic Zn 1Àx Co x O therefore has an effective layer composition for applications of quantum barriers. V C 2013 AIP Publishing LLC. [http://dx.

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“…For In x Ga 1-x N and Cd x Zn 1-x O alloys, it is known that electronic states in QWs are present either in the form of bound electron-hole pairs (localized excitons) or free electrons and holes (free excitons), as realized by carrier localization or delocalization, respectively. These electronic states give an influence to the quantum efficiency of In x Ga 1-x N and Cd x Zn 1-x O QWs, which is further dependent on temperature [21][22][23]. High quantum efficiency is based on excitonic localization at defect sites such as interface disorders and atom fluctuations.…”

Section: Recently Energy Coupling Between Qws and Sps Has Been Studimentioning

confidence: 99%

Exciton-Plasmon Interactions in Quantum Well Structures Near Silver Nanoparticles

Matsui¹

2018

Noble and Precious Metals - Properties, Nanoscale Effects and Applications

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The chapter reports photoluminescence (PL) and an energy transfer dynamic in a hybrid heterostructure consisting of an Ag nanoparticle (NP) layer and Cd 0.08 Zn 0.92 O/ZnO quantum well (QW). The observed PL quenching was closely related to electronic states of excitons confined in the QW. The PL quenching of the QW emission was only observed at low temperatures which excited carriers were radiatively recombined due to excitonic localization derived from fluctuated energy potentials in the QW. In contrast, delocalization of excitons from the QW with increasing temperature resulted in disappearance of the PL quenching. Time-resolved PL measurements revealed a decay rate of PL from the QW emission through the presence of energy transfer from the QW to Ag NP layer. The temperature-dependent energy-transfer rate was similar to that of the radiative recombination rate. The Ag NP layer surface showed a visible light absorption caused by localized surface plasmons (LSPs), which was very close to the PL peak energy of the QW. These results indicated that the excitonic recombination energy in the QW was nonradiatively transferred to Ag NP layer owing to energy resonance between the LSP and the QW. These phenomena could be explained by a surface energy transfer mechanism.

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Band alignment and excitonic localization of ZnO/Cd0.08Zn0.92O quantum wells

Cited by 13 publications

References 28 publications

Visible emission from ZnCdO/ZnO multiple quantum wells

Visible emission from ZnCdO/ZnO multiple quantum wells

Lattice, band, and spin engineering in Zn1−xCoxO

Exciton-Plasmon Interactions in Quantum Well Structures Near Silver Nanoparticles

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