The impact of heavy Ga doping on superconductivity in germanium
Сверхпроводимость и сверхтекучесть
DOI (Low Temperature Physics):
https://doi.org/10.1063/1.3671590Ключові слова:
superconducting semiconductors, heavily gallium-doped germanium, thin films.Анотація
We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at.%. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channelling, secondaryion- mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·1020 to 5.3·1020 cm–3 (0.4 to 1.2 at.%) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at.%. Higher concentrations lead to an increase of Tc from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m2 point to a large impact of the microstructure.
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Опубліковано
2011-08-22
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R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, A. Mücklich, M. Helm, and J. Wosnitza, The impact of heavy Ga doping on superconductivity in germanium: Сверхпроводимость и сверхтекучесть, Low Temp. Phys. 37, (2011) [Fiz. Nizk. Temp. 37, 1098-1106, (2011)] DOI: https://doi.org/10.1063/1.3671590.
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