Momentum-resolved electronic band structure and offsets in an epitaxial NbN/GaN superconductor/semiconductor heterojunction

TL;DR

This study uses advanced spectroscopy and calculations to analyze the electronic band structure and offsets at a NbN/GaN heterointerface, revealing key insights into their electronic alignment and potential for device applications.

Contribution

It provides the first momentum-resolved measurement of the electronic band structure and interfacial band offset in a NbN/GaN heterostructure, combining experimental and theoretical approaches.

Findings

Fermi states in NbN are aligned against GaN band gap, preventing electronic cross-talk.

The Schottky barrier height is confirmed by transport and optical measurements.

Momentum-resolved electronic properties are elucidated, advancing interface understanding.

Abstract

The electronic structure of heterointerfaces play a pivotal role in their device functionality. Recently, highly crystalline ultrathin films of superconducting NbN have been integrated by molecular beam epitaxy with the semiconducting GaN. We use soft X-ray angle-resolved photoelectron spectroscopy to directly measure the momentum-resolved electronic band structures for both NbN and GaN constituents of this Schottky heterointerface, and determine their momentum-dependent interfacial band offset as well as the band-bending profile into GaN. We find, in particular, that the Fermi states in NbN are aligned against the band gap in GaN, which excludes any significant electronic cross-talk of the superconducting states in NbN through the interface to GaN. We support the experimental findings with first-principles calculations for bulk NbN and GaN. The Schottky barrier height obtained from photoemission is corroborated by electronic transport and optical measurements. The momentum-resolved understanding of electronic properties elucidated by the combined materials advances and experimental methods in our work opens up new possibilities in systems where interfacial states play a defining role.