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- Gogova, D., et al.
(author)
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Investigation of the structural and optical properties of free-standing GaN grown by HVPE
- 2005
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 38:14, s. 2332-2337
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Journal article (peer-reviewed)abstract
- The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 νm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm-3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized. © 2005 IOP Publishing Ltd.
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| 3. |
- Gogova, Daniela, et al.
(author)
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Large-area free-standing GaN substrate grown by hydride vapor phase epitaxy on epitaxial lateral overgrown GaN template
- 2006
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In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 371:1, s. 133-139
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Journal article (peer-reviewed)abstract
- In this paper, the potential of the high growth rate hydride vapor phase epitaxy technique and laser lift-off for the fabrication of large-area (2?) free-standing GaN substrates is revealed. Structural and optical properties of 250-µm-thick GaN layer grown on a MOVPE epitaxial lateral overgrown GaN template have been investigated employing different analytical experimental techniques. A low value of dislocation density of ~1×107 cm-2 on the Ga-terminated face of the free-standing material was determined from AFM images. X-ray diffraction (XRD), Raman scattering measurements, and low-temperature photoluminescence (PL) were exploited to assess the structural and optical quality of the GaN. The full-width at half-maximum value of XRD ?-scans of the free-standing GaN material was determined to be 264 arcsec for the (101¯4) reflection. The XRD and low-temperature PL mapping measurements consistently proved the good crystalline quality and lateral homogeneity and small residual stress inside the material. Hence, the free-standing GaN achieved is highly advantageous for a lattice-constant and thermal-expansion-coefficient matched substrate for additional strain-free homoepitaxy of III-nitrides-based device heterostructures. © 2005 Elsevier B.V. All rights reserved.
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| 4. |
- Samsel-Czekala, M, et al.
(author)
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The electronic structure of UCoGe by ab initio calculations and XPS experiment
- 2010
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:1, s. 015503-
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Journal article (peer-reviewed)abstract
- The crystal and electronic structures of the orthorhombic compound UCoGe are presented and discussed. It has been either refined by the x-ray diffraction on a single crystal or computed within the local spin density functional theory, employing the fully relativistic version of the full-potential local-orbital band structure code, respectively. We particularly give our attention to investigating the Fermi surface and de Haas-van Alphen quantities of UCoGe. The calculated electronic density is then examined by x-ray photoelectron spectroscopy (XPS). Fairly good agreement is achieved between theoretical and experimental XPS results in the paramagnetic state. A small difference in the position (in energy scale) of the U 5f bands is caused by the electron localization effect observed in the experimental XPS. There is also some discrepancy for the Co 3d electron contributions below E-F. The Fermi surface in the non-magnetic state is of a semimetallic type while that in the ferromagnetic state, with the ordered moment of -0.47 mu(B)/f.u. along the c axis, is more metallic, with nesting properties that may favour superconductivity.
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