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Albrecht, Otto E.

doi:10.1093/gmo/9781561592630.article.06108

Cited by 7 publications

(15 citation statements)

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“…The GaN crystals grown by HPSG method are of high structural quality as determined by X-ray diffraction (XRD) [27], transmission electron microscopy (TEM) [12,28] and defect selective wet etching (etch pit density -EPD) techniques. The XRD data are summarized in Fig.…”

Section: Physical Properties Of Pressure Grown Gan Crystalsmentioning

confidence: 99%

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Near Defect Free GaN Substrates

Porowski

1999

MRS Internet j. nitride semicond. res.

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The current status of GaN crystallization under high nitrogen pressure will be presented. Both conductive and semi-insulating GaN crystals will be characterized.In particular the influence of Mg on the growth mechanisms will be discussed. The influence of Mg doping on morphology of Mg-doped crystals grown under pressure and Mg-doped homoepitaxial layers will be shown. It will be also shown that the addition of about 1 at.% of Mg into the solution improves significantly the structural quality of crystals reducing dislocation density at least by 3 orders of magnitude comparing to the crystals grown without an intentional doping. As it was estimated by selective wet etching and transmission electron microscopy the dislocation densities in the Mg-doped GaN is as low as 10 cm−1. The introduction of Mg also lowers the optical absorption coefficients for energies below fundamental edge by 2 to 3 orders of magnitude what is explained by disappearance of defect related states in the gap.The procedures for preparation of atomically flat epi-ready (000 1 ) surfaces without subsurface damage will be described. It will be shown that high quality homoepitaxial layers growing by monoatomic steps are possible on these substrates.

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Section: Physical Properties Of Pressure Grown Gan Crystalsmentioning

confidence: 99%

“…A number of GaN crystals have been studied by TEM [12,13,28] especially the samples used for optimization of surface preparation procedures and epitaxial growth of layers and structures. In most observations the crystals were completely free of dislocations.…”

Section: Physical Properties Of Pressure Grown Gan Crystalsmentioning

confidence: 99%

Near Defect Free GaN Substrates

Porowski

1999

MRS Internet j. nitride semicond. res.

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“…Our following study of the V / Ru system is partially motivated by recent experimental evidence for the formation of ultrathin close-packed fcc or hcp V films in epitaxial V / Ru multilayers. 18 In this system, structural stabilities similar to Cr/ Ru ͑0001͒ thin films and superlattices 6 were observed. When the thickness of V is below three monolayers, V atoms adopt the hexagonal symmetry of the Ru ͑0001͒ substrate and show some indication of a ferromagnetic order with a small magnetic moment.…”

Section: Introductionmentioning

confidence: 68%

“…This suggests the possibility of stabilizing ultrathin hcp V films in V / Ru superlattices, as indicated in recent experiments. 18 The change of the magnetic property is also noticeable. For both V 3 ͑fcc͒Ru 5 and V 3 ͑bcc͒Ru 5 , the total magnetic moment of the whole cell is close to zero and each V atom becomes nonmagnetic as well.…”

Section: Superlattice Propertiesmentioning

confidence: 98%

“…When the V layers get thicker, V atoms spontaneously switch to the bcc structure revealing no magnetic moment. 18 The purpose of the present study is primarily to investigate theoretically the possible formation of stable magnetic moments of V in the close-packed structures of bulk formats or ultrathin multilayers. Therefore, in this paper, we report on systematic density functional calculations of thin V films on hcp ͑0001͒ Ru and also superlattice structures formed of V and Ru atomic layer stackings perpendicular to the hcp ͑0001͒ surface.…”

Section: Introductionmentioning

confidence: 99%

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Density-functional theory calculation of electronic and magnetic properties of hexagonalV∕Ruthin films and superlattices

Zhang

Guo

2005

Phys. Rev. B

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Stimulated by recent experimental evidence for the formation of ultrathin close-packed films of vanadium ͑V͒ and also indication of ferromagnetic order in epitaxial V / Ru multilayers, we have performed firstprinciples electronic structure and total energy calculations to study the stability and magnetism of the metastable hcp and fcc structures of V and also the effects of the surface and interface on these properties. The systems include ultrathin films of a few monolayers of V grown on hcp ͑0001͒ ruthenium ͑Ru͒ substrates and V / Ru superlattices as well as bulk bcc, fcc, and hcp structures. Our investigations are based on densityfunctional theory with local density approximation plus generalized gradient corrections. Both the frozen-core projector augmented-wave approach and the all-electron full-potential linearized augmented-plane-wave method are utilized. First, our calculations show that all three bulk structures are nonmagnetic at their respective minimal energy lattice constants. However, all the three structures transit first to a low-spin ferromagnetic phase and then to a high-spin phase as the lattices expand. Second, we find that thin films on hcp ͑0001͒ Ru with one monolayer of V in either hcp or fcc stacking sequence have a magnetic moment of the order of 1 B . A thin film of three monolayers of V in fcc stacking sequence is weakly ferromagnetic, though the other thin films with more than one monolayer of V are essentially nonmagnetic. A free-standing film of three V monolayers in hcp stacking sequence is also ferromagnetic with sizable magnetic moments. We also find that the V 2 ͑hcp͒ /Ru 6 ͑hcp͒ and V 3 ͑hcp͒ /Ru 5 ͑hcp͒ superlattices exhibit ferromagnetism with a small total magnetic moment of a few tenths of B . Lattice relaxation has the trend of decreasing the magnitude of the magnetic moments. All the other V n /Ru m ͑hcp͒ superlattices ͑n =1,4,5 and m =5,6 as well as n = 3 with fcc or bcc stacking sequence͒ are essentially nonmagnetic. Finally, our calculations show that the stacking sequence has significant effects on the formation of stable atomic magnetic moments of V and is also important for the energetic stability of these systems.

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Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

Buth

2006

The Journal of Chemical Physics

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We study the quasiparticle band structure of isolated, infinite (HF)∞ and (HCl)∞ bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods local molecular orbital algebraic diagrammatic construction (ADC) scheme and local crystal orbital ADC (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.

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Cited by 7 publications

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Near Defect Free GaN Substrates

Near Defect Free GaN Substrates

Density-functional theory calculation of electronic and magnetic properties of hexagonalV∕Ruthin films and superlattices

Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

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