Epitaxial Junction of Inversion Symmetry Breaking AlN and Centrosymmetric NbN: A Polarity Control of Wide-Bandgap AlN

The polarity control of AlN by epitaxial growth can enable the fabrication of wavelength conversion devices and innovative electronic devices based on nitride semiconductors. Conventional techniques for controlling the AlN polarity are based on oxygen-mediated growth mechanisms. In contrast, this study reports a technique to invert the polarity of wurtzite-type AlN using lattice-matched centrosymmetric NbN. The surface of AlN grown by sputtering on NbN/Al-polar AlN was atomically flat and highly crystalline. Structural analysis with scanning transmission electron microscopy revealed that the AlN grown on NbN/Al-polar AlN was N-polar. The proposed all-nitride epitaxial N-polar AlN/NbN/Al-polar AlN heterostructure did not contain oxide materials, which typically degrade the optical and electrical properties of AlN. Furthermore, the stability of the N-polar AlN/NbN interface was clarified by density functional theory calculations. These findings can contribute to the fabrication of structural defect-free vertical- and lateral-polarity structures based on AlN.