Heteroepitaxy and annealing studies of orthorhombic gallium oxide films on nanostructured AlN templates

We report on the growth and characterization of κ-Ga₂O₃ films grown at varying temperatures in the range of 450-700 ˚C by mist-CVD. All of the films are single-crystalline and phase-pure except for the two samples grown at 550 ˚C and 600 ˚C, which have (2̅ 01)-oriented β-Ga₂O₃ incorporated in them. Unlike the phase-pure films which exhibit hexagonal-shaped grains, the mixed-phase samples have rough and partially coalesced films with irregular-shaped grains due to the presence of two Ga₂O₃ phases growing along two different crystallographic orientations. Moreover, we found that annealing the κ-Ga₂O₃ films at 700 ˚C in ambient air led to improved crystalline quality and reduced grain size.