Lattice relaxation mechanism of ZnO thin films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy

Park, S. H.; Hanada, Takashi; Oh, D. C.; Minegishi, Tsutomu; Goto, Hiroki; Fujimoto, Gakuyo; Park, J. S.; Im, Il; Chang, Jae-Soo; Cho, M. W.; Yao, Takafumi; Inaba, Kazuaki

doi:10.1063/1.2813021

Cited by 50 publications

(23 citation statements)

References 9 publications

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“…Following these reports, several authors adopted this interpretation for different ZnO samples. 15,20,[34][35][36][37] However, a convergent picture concerning the defect identification and the electronic properties of the 3.333 eV line has not yet emerged as evidenced by the large variety of contradicting explanations for this emission in recent years. Even less is known about the often weaker lines between 3.33 and 3.35 eV which sporadically appear in combination with the Y 0 transition.…”

Section: Introductionmentioning

confidence: 95%

Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers

et al. 2011

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ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons (Y lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the Y 0 transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers (I lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all Y lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II-VI and III-V semiconductors.

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Section: Introductionmentioning

confidence: 95%

Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers

et al. 2011

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“…22,23 The extracted values of ∆E strain at the DX state in Fig. 3(d) could be further compared with the analytical expression under the strained Hamiltonian by presuming that the underlying mechanism of the strain effect upon spectrally shifting the DX peak is similar to that for the F X peak, 32 as verified by near-field scanning optical microscopy measurements from strained ZnO NWs:…”

Section: Resultsmentioning

confidence: 99%

“…Considering the thinner buffer layer compared to the strain relaxation range over approximately 200 nm, 22,23 a depth-dependent strain variation and the subsequent carrier localization in traps along the growth axis are expected, followed by the QSE in the tapered region. In order to spatially trace the influences of these effects in ZnO NNs, the PL was measured along the growth axis as a function of the incident angle θ of a laser beam, which was varied from 0…”

Section: Methodsmentioning

confidence: 99%

Distinctive mapping of strain and quantum size effects using depth-resolved photoluminescence in ZnO nanoneedles

Hwang

Baek

et al. 2016

AIP Advances

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In order to locate the spatially resolved influence of the strain, carrier localization, and quantum size effect (QSE) in tapered ZnO nanoneedles (NNs), the photoluminescence (PL) was measured as a function of the incident laser angle θ from 0• (normal to a surface) to 85• . With increasing θ, the excitation point is spatially restricted along the axis of the NNs and varies from the ZnO buffer/sapphire interface to the tips of the NNs. In this way, we identified a strain-induced blue-shift of 25.3 meV at the ZnO buffer/sapphire interface, which corresponds to a tensile strain of 0.319%. The influence of strain and the concomitant indications of carrier localization decreased as the excitation point moved to a higher location along the NNs with increasing θ whereas the QSE revealed an abrupt blue-shift near the tips of the NNs. Furthermore, timeresolved PL measurement as a function of the excitation angle was used to distinguish the strain effect from the QSE. We observed two spatially competing tendencies: (1) the decay times are influenced by the increase in the interfacial strain and (2) the decay times are influenced by the decrease in the diameter-dependent QSE near the tips of the tapered ZnO NNs. C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

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“…Additionally, being nanoparticles grown in a wet-chemical process, their crystal structure is not affected by strain with a growth substrate. For films less than 200 nm compressive strain in the lattice can exist [20]. Hydrogen being able to be an interstitial or substitutional donor, crystal strain could play a role in the energetics of the hydrogen incorporation into the lattice.…”

Section: Discussionmentioning

confidence: 99%

Robust conductivity changes in ZnO and MgZnO nanoparticle films from annealing in hydrogen ambient

Chava

Young

Sanchez

et al. 2011

2011 11th IEEE International Conference on Nanotechnology

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We report changes observed in the I-V characteristics of ZnO and MgZnO nanoparticle thin films after annealing in H 2 at sufficiently high temperatures. The nanoparticles were grown on insulating silicon substrates and had an average diameter of 30 nm. The devices were of a two terminal design, where the terminals consisted of two 25 μm diameter gold wires laid parallel to each other on the nanoparticle film to measure the current passing through the film. When exposed to H 2 gas at room temperature, no significant changes in the current-voltage behavior of the nanoparticles were observed relative to measurements done in vacuum. Annealing in H 2 below 100 ˚C also resulted in no significant change in the current. When annealed above 100 ˚C, we observed an increase of about a factor of twenty that was semi-permanent. The origin of the change in I-V characteristics of ZnO and MgZnO nanoparticles when annealed in H 2 will be discussed.Index Terms -ZnO and MgZnO nanoparticles, hydrogen ambient, nanoparticle conductivity.

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Lattice relaxation mechanism of ZnO thin films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy

Cited by 50 publications

References 9 publications

Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers

Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers

Distinctive mapping of strain and quantum size effects using depth-resolved photoluminescence in ZnO nanoneedles

Robust conductivity changes in ZnO and MgZnO nanoparticle films from annealing in hydrogen ambient

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