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- ItemDC conductivity and Seebeck coefficient of nonstoichiometric MgCuZn ferrites(Warsaw : De Gruyter Open, 2017-2-8) Madhuri, W.; Kiran, S. Roopas; Reddy, M. Penchal; Reddy, N. Ramamanohar; Kumar, K.V. SivaNonstoichiometric series of Mg0.5-xCuxZn0.5Fe1.9O4-δ where x = 0.0, 0.1, 0.15, 0.2 and 0.25 has been synthesized by conventional solid state reaction route. The single phase spinel structure of the double sintered ferrites was confirmed by X-ray diffraction patterns (XRD). The ferrite series was studied in terms of DC electrical conductivity and thermoelectric power in the temperature ranging from room temperature to 300 °C and 400 °C, respectively. It was observed that DC electrical conductivity and Seebeck coefficient α decreased with the increase in x. DC electrical conductivity was found to decrease by about 4 orders. All the compositions showed a negative Seebeck coefficient exhibiting n-type semiconducting nature. From the above experimental results, activation energy and mobility of all the samples were estimated. Small polaron hopping conduction mechanism was suggested for the series of ferrites. Owing to their low conductivity the nonstoichiometric MgCuZn ferrites are the best materials for transformer core and high definition television deflection yokes. © 2017 Wroclaw University of Science and Technology.
- ItemShallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology(Weinheim : Wiley-VCH, 2019) Sammak, Amir; Sabbagh, Diego; Hendrickx, Nico W.; Lodari, Mario; Wuetz, Brian Paquelet; Tosato, Alberto; Yeoh, LaReine; Bollani, Monica; Virgilio, Michele; Schubert, Markus Andreas; Zaumseil, Peter; Capellini, Giovanni; Veldhorst, Menno; Scappucci, GiordanoBuried-channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 10 5 cm 2 V −1 s −1 ) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top-gate of a dopant-less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 10 11 cm −2 , light effective mass (0.09m e ), and high effective g-factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim