  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.
