Superconducting Tunnel Junctions (STJs) are fascinating devices that rely on the Josephson effect for a variety of possible applications, including photon detection. At their most basic, they consist of an insulating material sandwiched between two superconducting plates. Quantum tunneling allows electrons to flow through the insulating material, while the absorption of photons in the superconducting layer can break Cooper pairs, freeing more excess carriers to pass the junction. In this work, the Authors describe the fabrication and photo-response of an STJ with niobium nitride (NbN) as the superconductor, and gallium nitride (GaN) as the insulator. Due to the precisely controlled epitaxial growth of the superconductor on the semiconductor, the defect density in the interface could be tuned. The presence of the coherence peaks in the tunneling conductivity demonstrated the quality of the interface created with this fabrication technique. To further demonstrate the capabilities of their device, the Authors also show power dependent photo-response from the junction, highlighting the potential for photon energy resolution in future devices. This work shows us a path to being able to design STJs that can be tuned (through the doping of the semiconductor barrier) for a specific application and fabricated using large scale processes.
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