Thin-film Superconductivity in Ga-doped Germanium

We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga-doping levels up to 6%, not accessible to any other preparation method so far. The superconducting critical parameters strongly depend on the annealing conditions. Transport measurements reveal Tc up to 0.5 K and anisotropic Bc(T) with a linear temperature dependence reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], this work reports another unexpected observation of superconductivity in doped elemental semiconductors. Our fabrication techniques are compatible to industrial semiconductor processing and allow for on-chip superconductivity in integrated circuits.