Low-temperature transport properties of Si and Ge films with Ga-rich nanoprecipitates

Ga-rich (~ 10 at.%) Si and Ge films were fabricated by high-fluence Ga+ ion implantation through a SiO2 capping layer. The structure and the electrical transport properties of these films have been studied after flash-lamp [1-3] and rapid thermal annealing [4, 5]. Amorphous, Ga-rich nanoprecipitates are embedded in a heavily p-type doped semiconductor matrix [3, 4]. These nanoprecipitates become superconducting below critical temperatures up to 7 K. They can interact due to the proximity effect in the degenerately doped semiconductor matrix and form a random network of Josephson junctions. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. In particular, Ga-rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance [6, 7] . The possibility to prepare and modify Ga-rich Si and Ge films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [1] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, et al., Phys. Rev. Lett.,2009, 102, 217003. [2] R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, et. al., Low Temp. Phys., 2011, 37, 1098. [3] V. Heera, J. Fiedler, M. Naumann, R. Skrotzki, et al., Supercond. Sci. Technol., 2014, 27, 055025. [4] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2011, 83, 214504. [5] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2012, 85, 134530. [6] V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, et al., Appl. Phys. Lett., 2012, 100, 262602 [7] V. Heera, J. Fiedler, R. Hübner, B. Schmidt, et al., New. J. Phys., 2013, 15, 083022