Evolution of -Ga₂O₃ to -Ga₂O₃ solid-solution epitaxial films after high-temperature annealing

Atomic resolution scanning/transmission electron microscopy (S/TEM) and energy-dispersive x-ray (EDX) analysis were used to determine the effects of annealing at 800-1000 degrees C in air on Ga2O3 films grown on (100) MgAl2O4 at 650 degrees C via metal-organic chemical vapor deposition. Annealing resulted in the diffusion of Mg and Al into the films concomitantly with the transformation of beta-Ga2O3 to gamma-Ga2O3 solid solutions. The minimum atomic percent of Al + Mg that corresponded with the transformation was similar to 4.6 at. %. Analyses of atomic-scale STEM images and EDX profiles revealed that the Al and Mg atoms in the gamma-Ga2O3 solid solutions occupied octahedral sites; whereas the Ga atoms occupied tetrahedral sites. These site preferences may account for the stabilization of the gamma-Ga2O3 solid solutions.