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Jeudi 12 Decembre 2014, 14h
Amphi Holweck, Esc C, 1ème etage
Superconducting Silicon and Josephson junctions
Francesca Chiodi
IEF Université Paris XI
Even though silicon is one of the most studied materials, superconductivity at ambient pressure in boron doped silicon has only been discovered in 2006 [1]. This is due to the extreme doping concentration required to trigger superconductivity in this system, more than three times the boron solubility limit in silicon. This concentration is impossible to reach using conventional micro-electronic techniques but epitaxial superconducting Si:B thin films can be achieved using Gas Immersion Laser Doping.
We show that superconductivity is only observed for boron concentration values exceeding a threshold value, which is inversely proportional to the thin layer thickness. The critical temperature then rapidly increases and is fully determined by the boron dose[2] .
Superconducting silicon also excites a great interest concerning its possible applications. The great asset of superconducting silicon is the possibility to take advantage from the silicon technology to elaborate built-in structures in a single Si crystal, avoiding the assembling step. Since Si:B doesn’t transit directly from the semiconducting state to the superconducting one, but first becomes metallic, it allows the fabrication of a large range of nanodevices, in which superconductors, metals and semiconductors can be coupled through extremely clean, epitaxially grown interfaces.
We demonstrate the possibility of nano-structuring the strongly boron-doped Si to realise superconducting nanodevices, and we show the first results on all Si:B Superconductor-Normal metal Josephson junctions.
[1] E. Bustarret et al., Nature 444, 465 (2006)
[2] A. Grockowiak et al., Phys. Rev. B 88, 064508 (2013)