Superconductivity in thin-film germanium in the temperature regime around 1 K

We report recent discoveries of superconductivity in p-type-doped germanium which has been fabricated by implantation of gallium ions into near-intrinsic cubic Ge. Depending on the detailed preparation and annealing conditions, we demonstrate that superconductivity can be generated and tailored in thin p-doped layers of the Ge host. By carefully adjusting the annealing parameters, we have been able to raise the onset temperature of superconductivity to about 1.4 K at a Ga peak concentration of ∼10 at.%. This progress and the large in-plane critical magnetic field of about the size of the Chandrasekhar–Clogston limit makes thin-film Ga-doped Ge (Ge:Ga) even more attractive for technological applications. There might be particular interest to utilize on-chip thin-film superconductivity in a semiconducting environment as our preparation method of Ge:Ga is fully compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining ‘islands of the periodic table of elements’ on which superconductivity has not been found so far.