Superconductivity of p-Type Doped Ge

We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using Ga as dopant, we have produced a series of GeGa_x samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 14%, i.e. a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with T_c up to 0.39 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field re ecting the two-dimensional character of the superconducting state in the thin GeGa_x layer having an effective depth of only 20 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors.