Characterization of Ga-face/Ga-face and N-face/N-face interfaces with antiparallel polarizations fabricated by surface-activated bonding of freestanding GaN wafers

Electrical properties of heterojunctions of group-III nitrides are largely sensitive to interface charges due to the discontinuity of polarizations. By means of surface-activated bonding of double-side polished freestanding GaN (0001) wafers, we fabricate Ga-face/Ga-face and N-face/N-face interfaces with antiparallel spontaneous polarizations, i.e. interfaces with the greatest discontinuity of polarizations, to investigate their electrical and nanostructural properties. Built-in potential of N-face/N-face interface is smaller than that of Ga-face/Ga-face interface after a post-bonding annealing at 600 °C. The difference in built-in potentials between the two antiparallel polarized interfaces is analyzed in the framework of charge-neutrality-level model with effects of antiparallel polarizations incorporated, and the density of interface states is roughly estimated. The leak is enhanced in both Ga-face/Ga-face and N-face/N-face interfaces by annealing at higher temperatures. Contribution of defects observed in the vicinity of bonding interfaces is suggested.