Momentum-resolved electronic structure and band offsets in an epitaxial NbN/GaN superconductor/semiconductor heterojunction
Tianlun Yu, John Wright, Guru Khalsa, Betül Pamuk, Celesta S. Chang, Yu. Matveyev, Xiaoqiang Wang, Thorsten Schmitt, Donglai Feng, David A. Muller, Huili Grace Xing, Debdeep Jena, Vladimir N. Strocov
Abstract
The electronic structure of heterointerfaces is a pivotal factor for their device functionality. We use soft x-ray angle-resolved photoelectron spectroscopy to directly measure the momentum-resolved electronic band structures on both sides of the Schottky heterointerface formed by epitaxial films of the superconducting NbN on semiconducting GaN, and determine their momentum-dependent interfacial band offset as well as the band-bending profile. We find, in particular, that the Fermi states in NbN are well separated in energy and momentum from the states in GaN, excluding any notable electronic cross-talk of the superconducting states in NbN 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 of interfaces elucidated in our work opens up new frontiers for the quantum materials where interfacial states play a defining role.