Electronic structure of the all-epitaxial NbN/GaN interface

The all-epitaxial integration of the NbN superconductor with Group III-Nitride direct-band-gap semiconductors by molecular beam epitaxy has created an opportunity for scalable, integrated superconductor/semiconductor devices. Paramount to our understanding of this novel hybrid system is concrete identification of the electronic structure of both materials at their interface. While the electronic structure of III-Nitrides are well-understood, the electronic structure of NbN – an important superconductor due to its large critical temperature – has only been reported theoretically, eluding experimental verification.

We present a combined experimental and theoretical study of the electronic structure of the all-epitaxial NbN/GaN interface using soft-X-ray angle-resolved photoemission spectroscopy and first-principles calculations. Measuring the band structure of the NbN/GaN interface, we place the chemical potential safely in the GaN gap, with the chemical potential ~1 eV below the GaN conduction band. Using state-of-the-art first-principles theory we update the electronic structure picture of NbN, discuss its importance in the context of superconductivity in strained NbN, and its coupling to III-Nitride semiconductors.