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Depth-resolved transport measurements and atom-probe tomography of heterogeneous, superconducting Ge:Ga films

: Heera, V.; Fiedler, J.; Naumann, M.; Skrotzki, R.; Kölling, S.; Wilde, L.; Herrmannsdörfer, T.; Skorupa, W.; Wosnitza, J.; Helm, M.


Superconductor Science and Technology 27 (2014), Nr.5, Art.055025, 6 S.
ISSN: 0953-2048
ISSN: 1361-6668
Deutsche Forschungsgemeinschaft DFG
HE 2604/7-1
Fraunhofer IPMS ()

Ge films with a mean Ga content of about 8 and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change in the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters of up to 10 000 atoms. Since no percolating Ga clusters exist, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.