Superconducting layers in semiconductors – Ready for the quantum interference?

Superconductivity is a fascinating ground state of matter and has been discovered one century ago. A new debate about the fundamental physical background and technological potential of superconducting group-IV semiconductors occurred, since superconductivity at ambient pressure conditions was shown for boron doped diamond [1] and silicon [2]. These unusual superconductors open the way towards new microelectronic devices and applications.
In our previous work, we used Ga-ion implantation and subsequent short-time annealing for creating highly Ga doped layers in Ge. [3] These layers show an intrinsic superconducting transition at temperatures below 1 K because of the high doping level. [4] In a next step we could show the feasibility to stabilize Ga-rich layers at SiO₂/Si [5,6] and SiO₂/Ge [7] interfaces by using a 30 nm SiO₂ cover layer during implantation and annealing.
The presented structural investigations by means of Rutherford Backscattering Spectrometry (RBS) and cross-sectional Transmission Electron Microscopy (XTEM) reveal the presence of a 10 nm thin, superconducting layer at the interfaces containing Ga-rich precipitates. In both cases the critical temperature increases to 7 K which is comparable to amorphous Ga and therefore enables the detailed investigation of the influence of superconducting precipitates on the superconducting properties of doped semiconductor layers.
However, the previous investigations were done on 1 x 1 cm² size samples. The possibility of fabricating superconducting microstructures in Si with standard microelectronic lithography will be shown. Theses microstructures still undergo a superconducting transition below 7 K. High critical magnetic fields in the range of 10 T and high critical current densities of 50 kA/cm² were achieved. For applications in superconducting microelectronics a Josephson-Junction has to be implemented. [8] We plan to use a Focused Ion Beam (FIB) for this task. Details about the sample processing, layer microstructure and processing of superconducting microstructures will be presented.

[1] E. A. Ekimov et al., Nature (London) 428 (2004) 542.
[2] E. Bustarret et al., Nature 444 (2006) 465.
[3] V. Heera et al., J. Appl. Phys. 107 (2010) 053508.
[4] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003.
[5] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505.
[6] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.
[7] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530.
[8] J. Q. You et al., Nature 474 (2011) 589.