Microscopic spatial distribution of bound excitons in high-quality ZnO

Bertram, F.; Förster, D.; Christen, J.; Oleynik, N.; Dadgar, A.; Krost, A.

doi:10.1016/j.jcrysgro.2004.08.036

Cited by 4 publications

(4 citation statements)

References 14 publications

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“…This analysis, based on the correlation between monochromatic CL images and TEM images, shows that the emissions at 220 nm and 227 nm are related to these structural defects: grain boundaries and dislocations. Such a spatial localization of the emitted light has already been observed in the luminescence from excitons bound to defects or impurities in III-V or II-VI semiconductors [21,22,23]. In our case, the CL images filtered at 220 nm and 227 nm display the same spatial light distribution.…”

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confidence: 83%

Origin of the excitonic recombinations in hexagonal boron nitride by spatially resolved cathodoluminescence spectroscopy

Jaffrennou

Barjon

Lauret

et al. 2007

Journal of Applied Physics

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The excitonic recombinations in hexagonal boron nitride (hBN) are investigated with spatially resolved cathodoluminescence spectroscopy in the UV range. Cathodoluminescence images of an individual hBN crystallite reveals that the 215 nm free excitonic line is quite homogeneously emitted along the crystallite whereas the 220 nm and 227 nm excitonic emissions are located in specific regions of the crystallite. Transmission electron microscopy images show that these regions contain a high density of crystalline defects. This suggests that both the 220 nm and 227 nm emissions are produced by the recombination of excitons bound to structural defects.Hexagonal Boron Nitride (hBN) is a wide band gap semiconductor [1,2,3,4] isostructural with graphite. For a few years, much interest has been devoted to BN materials since hBN and more specifically BN nanotubes [5,6,7,8,9,10,11,12,13] are expected to be promising materials for optoelectronic applications. Recently, experimental and theoretical studies have been undertaken in order to investigate the optical properties of hBN. Using luminescence experiments, the near band-edge emission has been observed in the UV region [14,15,16,17,18]. Theoretical groups have interpreted this UV emission as due to unusually strong excitonic effects [3,4]. They propose that excitons in hBN are closer to Frenkel-type excitons with large binding energy (0.7 eV) than to the usual Wannier-like excitons of classical III-N semiconductors.The hBN near-band edge emission consists in several peaks at 215 nm (5.77 eV), 220 nm (5.63 eV) and 227 nm (5.46 eV) [15]. Watanabe et al. [16] recently observed that this UV band shows drastic changes after deformation of a single crystal [16,17]. By pressing a hBN single crystal between two fingers, the authors show that the relative intensities of the 215 nm and 227 nm bands are reversed. After deformation, the CL intensity of the 215 nm band becomes negligible as compared to the 227 nm band which is then predominant. According to recent calculations [3], the 215 nm luminescence band has been attributed to Frenkel-type free excitonic recombinations and Watanabe et al. tentatively assign the 227 nm band, which appears predominantly after deformation, to exci- * Electronic address: francois.ducastelle@onera.fr tons bound to stacking faults or to the shearing of lattice planes [16].In this work, we present a detailed investigation of the excitonic luminescence in hBN. By combining spatially resolved cathodoluminescence (SR-CL) spectroscopy with a structural analysis of the crystal by means of Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses, we investigate the nature of the 220 nm and 227 nm excitonic recombinations in terms of excitons bound to well identified structural defects.In these experiments, commercial Aldrich hBN powders are used. The samples were dispersed in ethanol and deposited on carbon coated TEM copper grids in order to isolate individual hBN crystallites. Commercial Starck hBN powders were also inve...

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confidence: 83%

Origin of the excitonic recombinations in hexagonal boron nitride by spatially resolved cathodoluminescence spectroscopy

Jaffrennou

Barjon

Lauret

et al. 2007

Journal of Applied Physics

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“…Evidence has been seen in many cases for inhomogeneities in the emission, and the I 0 /I 1 line has been shown to be strongest at grain boundaries in heteroepitaxial thin films, though its origin remains unclear. The peak wavelengths of the (Ga-related) I 8 line and other emissions have been shown to depend on the local strain in these samples and show greatest spectral shifts close to the substrate-film interface and also at grain boundaries where crystallites have coalesced during growth [9,10]. For homoepitaxial thin films the dominant I 6 (Al-related) emission is reported to be quite homogeneously distributed in the sample [8].…”

Section: Introductionmentioning

confidence: 86%

“…Different dopants including N, P (p-type) and Ga, Al (ntype) are commonly used. The distribution of dopants within ZnO thin films has been studied by various authors using micro-photoluminescence (μ-PL), cathodoluminescence (CL) spectroscopy and scanning probe electrical techniques [8][9][10]. Evidence has been seen in many cases for inhomogeneities in the emission, and the I 0 /I 1 line has been shown to be strongest at grain boundaries in heteroepitaxial thin films, though its origin remains unclear.…”

Section: Introductionmentioning

confidence: 99%

Spatial inhomogeneity of donor bound exciton emission from ZnO nanostructures grown on Si

Biswas¹,

Kwack²,

Dang³

et al. 2009

Nanotechnology

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We report low temperature cathodoluminescence spectroscopy measurements of the band edge emission from ZnO nanostructures grown by vapour phase transport on Si. A range of donor bound exciton emission lines are found and the Al-related emission at 3.3605 eV in particular shows a marked inhomogeneity in its distribution throughout the sample. Increased 3.3605 eV emission is seen at a range of locations in nanorods and nanosheets where different nanostructures cross or coalesce, suggesting aggregation of Al donors in ZnO in regions of crystal structure disruption. However, localized crystal structure disruption appears to be a necessary rather than a sufficient condition for Al aggregation, since increased 3.3605 eV emission is seen only in such regions, but not all such regions show increased emission, implying that the microscopic nature of such regions is important in determining Al aggregation. Supporting data are presented from well-aligned, non-crossing, nanorods on a-sapphire.

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“…By varying the accelerating voltage and current of the electron beam, one can control the penetration depth and the density of injected carriers [10]. Many researches on the CL of ZnO have been reported, while the UV luminescence efficiency is associated with only the crystalline quality in most cases [9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Therefore, only the green luminescence band has attracted interests for ZnO:Zn in CL as well as in photoluminescence (PL) where the UV luminescence is hard to be observed at room temperature [8,[26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Nano-scale distribution of ZnO free exciton luminescence in ZnO:Zn microcrystals and its modification under electron beam excitation

Ichimiya

Horii

Hirai

et al. 2006

J. Phys.: Condens. Matter

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The dependences of cathodoluminescence (CL) from ZnO:Zn phosphor powder upon local space, accelerating voltage and beam current have been investigated at room temperature. Ultraviolet (UV) luminescence, which is hard to be observed in photoluminescence (PL) at room temperature, has been clearly observed in CL as well as green luminescence. The intensity ratio of the UV luminescence to the green one varies from point to point. From the comparison with PL, the UV luminescence is attributed to the recombination of ZnO free excitons. The UV luminescence is little observed at low accelerating voltage where, similar to the excitation light for PL measurement, the electron beam penetrates into only the surface depletion layer where free excitons are unstable due to the surface electric field. However, the UV luminescence from the depletion layer becomes observable at large beam current because of the suppression of the electric field in the depletion layer caused by injected electrons.

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Microscopic spatial distribution of bound excitons in high-quality ZnO

Cited by 4 publications

References 14 publications

Origin of the excitonic recombinations in hexagonal boron nitride by spatially resolved cathodoluminescence spectroscopy

Origin of the excitonic recombinations in hexagonal boron nitride by spatially resolved cathodoluminescence spectroscopy

Spatial inhomogeneity of donor bound exciton emission from ZnO nanostructures grown on Si

Nano-scale distribution of ZnO free exciton luminescence in ZnO:Zn microcrystals and its modification under electron beam excitation

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