Quantum Transport in 2DEGs in Epitaxial GaN Quantum Wells on Superconducting NbN

The epitaxial integration of superconducting NbN with III-N semiconductors was previously demonstrated in our report [Yan et al, Nature 555, 183-189 (2018)]. We have investigated the magnetotransport properties in this superconductor/semiconductor heterostructure, of the two-dimensional electron gas (2DEG) in the GaN quantum well in magnetic fields up to 35 Tesla. The 2DEGs exhibited strong Shubnikov-de Haas (SdH) oscillations that showed indications of spin-splitting as well as Hall-effect resistance plateaus that approach the quantum Hall regime. By varying a gate voltage to sweep the Fermi level, we directly observe the change in carrier concentration through SdH measurements. The associated change in occupation of Landau levels allows us clear access down to the 3^rd Landau level. We report our observations of electron scattering processes due to dislocations near the gate-induced pinchoff point of the transistor and compare the scattering of N-polar and Ga-polar HEMTs. We comment on possibility of reaching the quantum Hall state in this material system, which would open a path towards realizing proximitized quantum Hall and superconducting states in a superconductor/semiconductor heterostructure.