Properties of epitaxial superconductor/semiconductor heterostuctures

The possibility of creating lattice-matched heterostructures of superconductors and semiconductors olds the promise of combining the best of both electronic phases of matter. In this work, we report the physical properties of epitaxial niobium nitride/gallium nitride superconductor/semiconductor heterojunctions. We measure the energy band offsets by transport and capacitance measurements, as well as the individual bandstructures by photoelectron spectroscopy. By determining the band offsets, we identify the required semiconductor composition that is required to form a transparent barrier. We also discuss the injection of supercurrent into the semiconductor and its transport in the semiconductor.