We demonstrate high-quality monocrystalline NbN films deposited by DC magnetron sputtering on a GaN/AlN waveguiding heterostructure. NbN layers with a thickness of 8 nm are grown along the [111] direction, and show two orientation domains with NbN(111) [2-1-1]//AlN (0001) [10-10] and NbN(111) [2-1-1]//AlN(0001) [01-10] epitaxial relationships. Our NbN films display a critical temperature of 13.2 K, with the superconducting transition taking place in a temperature range of only 0.7 K.
