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search.filters.applied.f.access: openAccess × End date: 2019 × Start date: 2018 × DDC: 540 × DDC: 660 × WGL Institute: IKZ ×

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    REScO3 Substrates—Purveyors of Strain Engineering
    (Weinheim : Wiley-VCH, 2019) Klimm, Detlef; Guguschev, Christo; Ganschow, Steffen; Bickermann, Matthias; Schlom, Darrell G.
    The thermodynamic and crystallographic background for the development of substrate crystals that are suitable for the epitaxial deposition of biaxially strained functional perovskite layers is reviewed. In such strained layers the elastic energy delivers an additional contribution to the Gibbs free energy, which allows the tuning of physical properties and phase transition temperatures to desired values. For some oxide systems metastable phases can even be accessed. Rare-earth scandates, REScO3, are well suited as substrate crystals because they combine mechanical and chemical stability in the epitaxy process with an adjustable range of pseudo-cubic lattice parameters in the 3.95 to 4.02 Å range. To further tune the lattice parameters, chemical substitution for the RE or Sc is possible. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Growth and Properties of Intentionally Carbon-Doped GaN Layers
    (Weinheim : Wiley-VCH, 2019) Richter, Eberhard; Beyer, Franziska C.; Zimmermann, Friederike; Gärtner, Günter; Irmscher, Klaus; Gamov, Ivan; Heitmann, Johannes; Weyers, Markus; Tränkle, Günther
    Carbon-doping of GaN layers with thickness in the mm-range is performed by hydride vapor phase epitaxy. Characterization by optical and electrical measurements reveals semi-insulating behavior with a maximum of specific resistivity of 2 × 1010 Ω cm at room temperature found for a carbon concentration of 8.8 × 1018 cm−3. For higher carbon levels up to 3.5 × 1019 cm−3, a slight increase of the conductivity is observed and related to self-compensation and passivation of the acceptor. The acceptor can be identified as CN with an electrical activation energy of 0.94 eV and partial passivation by interstitial hydrogen. In addition, two differently oriented tri-carbon defects, CN-a-CGa-a-CN and CN-a-CGa-c-CN, are identified which probably compensate about two-thirds of the carbon which is incorporated in excess of 2 × 1018 cm−3. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Lithium metal penetration induced by electrodeposition through solid electrolytes: Example in single-crystal Li6La3ZrTaO12 garnet
    (Pennington, NJ : Electrochemical Society, 2018) Swamy, Tushar; Park, Richard; Sheldon, Brian W.; Rettenwander, Daniel; Porz, Lukas; Berendts, Stefan; Uecker, Reinhard; Carter, W. Craig; Chiang, Yet-Ming
    Solid electrolytes potentially enable rechargeable batteries with lithium metal anodes possessing higher energy densities than today’s lithium ion batteries. To do so the solid electrolyte must suppress instabilities that lead to poor coulombic efficiency and short circuits. In this work, lithium electrodeposition was performed on single-crystal Li6La3ZrTaO12 garnets to investigate factors governing lithium penetration through brittle electrolytes. In single crystals, grain boundaries are excluded as paths for lithium metal propagation. Vickers microindentation was used to introduce surface flaws of known size. However, operando optical microscopy revealed that lithium metal penetration propagates preferentially from a different, second class of flaws. At the perimeter of surface current collectors smaller in size than the lithium source electrode, an enhanced electrodeposition current density causes lithium filled cracks to initiate and grow to penetration, even when large Vickers defects are in proximity. Modeling the electric field distribution in the experimental cell revealed that a 5-fold enhancement in field occurs within 10 micrometers of the electrode edge and generates high local electrochemomechanical stress. This may determine the initiation sites for lithium propagation, overriding the presence of larger defects elsewhere.
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    Static Dielectric Constant of β-Ga2O3 Perpendicular to the Principal Planes (100), (010), and (001)
    (Pennington, NJ : ECS, 2019) Fiedler, A.; Schewski, R.; Galazka, Z.; Irmscher, K.
    The relative static dielectric constant ℇr of β-Ga2O3 perpendicular to the planes (100), (010), and (001) is determined in the temperature range from 25 K to 500 K by measuring the AC capacitance of correspondingly oriented plate capacitor structures using test frequencies of up to 1 MHz. This allows a direct quantification of the static dielectric constant and a unique direction assignment of the obtained values. At room temperature, ℇr perpendicular to the planes (100), (010), and (001) amounts to 10.2 ± 0.2, 10.87 ± 0.08, and 12.4 ± 0.4, respectively, which clearly evidence the anisotropy expected for β-Ga2O3 due to its monoclinic crystal structure. An increase of ℇr by about 0.5 with increasing temperature from 25 K to 450 K was found for all orientations. Our ℇr data resolve the inconsistencies in the previously available literature data with regard to absolute values and their directional assignment and therefore provide a reliable basis for the simulation and design of devices. © The Author(s) 2019.