Fabrication and Characterization of Superconducting Films for Superconductor-Topological Insulator Hybrid Devices

Proximation of s-wave superconductivity to topological materials is an effective way to realize Majorana modes in condensed matter physics. In order to fabricate a successful device, the superconducting material plays a crucial role since selection of material, growth method, applicable critical temperature, adequate critical magnetic field, transparent electrical contact, and thus proper work function, needs to be deliberately considered. Here, we report the fabrications and transport measurements for two types of superconducting thin films, tantalum (Ta) and niobium nitride (NbN), at various growth conditions. Both Ta and NbN films show applicable potentials as the superconducting electrodes. We also demonstrate the proximity effect induced supercurrent state in an InAs/GaSb bilayer device with superconducting Ta electrodes.