Sputter epitaxy of transition metal nitrides for ferroelectric and superconducting applications

Transition metal nitrides such as NbN and ScAlN are promising for integrating superconducting and ferroelectric functionalities into nitride semiconductor platforms. We studied the sputter epitaxy of NbN and ScAlN films on AlN- and GaN-based substrates. NbN exhibited a phase transition from cubic to hexagonal structures depending on the growth temperature and enabled polarity inversion of AlN, relevant for nonlinear optical applications. ScAlN films on GaN heterostructures showed coherent wurtzite epitaxy with smooth surfaces. Electrical measurements revealed that higher growth temperatures increased sheet carrier concentration and mobility, indicating potential as a GaN HEMT barrier. Ferroelectricity in ScAlN was confirmed using metal–ferroelectric–semiconductor structures on n-type GaN, showing clear polarization switching. Leakage current behavior varied with growth conditions and Sc content. These results highlight the potential of sputtered transition metal nitrides for next-generation electronic and quantum devices.