Superconducting Ge thin films by molecular beam epitaxy for quantum information*

Extreme doping concentrations in group IV semiconductors has been shown to induce not only the expected metal-insulator transition [1] but also at high enough compositions (~5% or more), superconductivity is achieved [2]. However, all reports of such superconductors are grown through highly non-equilibrium growth methods such as laser or ion implantation with subsequent annealing. These methods suffer from difficulties in controlling resultant film thickness [2] or scalability [3]. Here, we will discuss our work on doped Ga:Ge films grown by molecular beam epitaxy (MBE) that show superconductivity. We report growth parameter phase space and the resulting film electronic properties. Our MBE-grown films display T_c ~ 0.8K-2K, B_c^oop ~ 0.05T-0.25T, and B_c^IP ~ 0.3T-1.3T, displaying significant reliance on film thickness. The key links between film growth parameters and resulting critical temperature and field will be discussed.

[1] C. Persson, et. al., Phys. Rev. B. 63, 205119 (2001).

[2] K. Sardashti, et. al., Appl. Phys. Lett. 118, 073102 (2021).

[3] D. Cammilleri, et. al., Thin Solid Films 517, 75-79 (2008).