Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Since superconductivity has been discovered one century ago, scientists search for new materials that show this fascinating ground state of matter. Recent investigations on superconductivity of elemental group-IV semiconductors like diamond [1] and silicon [2] lead to a new debate about the mechanism and technological potential of these unusual superconductors.
In our previous work, we have shown the possibility of creating highly Ga doped Ge layers via Ga-ion implantation and subsequent short-time annealing. As a consequence of the high doping level, these layers are intrinsically superconducting below 1 K [3]. Furthermore we investigated the feasibility of embedding superconducting layers in Si-SiO₂ heterostructures not via doping but by Ga precipitation reaching critical temperatures of 7 K [4] with equivalent processing steps.
From these investigations, the question arises if it is possible to combine highly doped semiconducting regions with intrinsic and extrinsic superconducting structures having different critical temperatures. We used again Ga implantation in Ge covered by a 30 nm SiO₂ layer and flash-lamp annealing to create a complex layer structure showing various transitions in different superconducting states. The first transition occurs at 7 K and can be attributed to Ga-rich precipitates at the Ge-SiO₂ interface. Due to the superconductivity of the underlying highly doped germanium layer, a second transition is observed at around 1 K. Recent results on the structural and electrical properties of the heterostructures will be presented.

[1] E. A. Ekimov et al., Nature (London) 428, 542 (2004).
[2] E. Bustarret et al., Nature 444, 465 (2006).
[3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102, 217003 (2009); V. Heera et al., Journal of Applied Physics 107, 053508 (2010).
[4] J. Fiedler et al., Phys. Rev. B 83, 214504 (2011); R. Skrotzki et al., Appl. Phys. Lett. 97 192505 (2010).