Heteroepitaxy and Annealing Studies of Orthorhombic Gallium Oxide Films on Nanostructured AlN Templates

We report on the growth and characterization of kappa-Ga2O3 films grown at varying temperatures in the range of 450-700 degrees C by mist-CVD. All of the films are single-crystalline and phase-pure except for the two samples grown at 550 degrees C and 600 degrees C, which have ( (2) over bar 01)-oriented beta-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 kappa-Ga2O3 films at 700 degrees C in ambient air led to improved crystalline quality and reduced grain size.