In situ atomic-resolution study of transformations in double polymorph /-Ga₂O₃ structures

Disorder-induced formation of metastable Ga2O3 polymorphs as well as the recovery of the stable state upon annealing attract attention because of the fundamental novelty and rapidly increasing interest in the use of Ga2O3 in practical applications. In this study, double polymorph gamma/beta-Ga2O3 structures fabricated by the radiation-induced disorder approach were used as a starting point for systematic in situ annealing electron microscopy experiments. We show that, under the conditions of the TEM in situ annealing, double gamma/beta-Ga2O3 polymorph structures remained stable up to 300(degrees)C, when onsets of the gamma-to-beta transformation become traceable, leading to a prominent gamma- and beta-mixture already at 500 C-degrees. Interestingly, the recrystallization of the beta-Ga2O3 occurs throughout the whole gamma-film and the preferential alignments at the newly emerging gamma/beta-interfaces are different from that of the initial gamma/beta-interface formed as a result of the disorder-induced ordering. The alignments of the two polymorphs are maintained as a function of temperature - with a reduction in the volumetric ratio of gamma-domains for increasing annealing temperature. Finally, at 1100 C-degrees, gamma-Ga2O3 fully transforms into beta-Ga2O3 , without dominating crystallographic relationships or preferred orientations, indicating that energy barriers are not any longer implied limiting factors, because of a sufficiently high thermal energy supply. Thus, these TEM in situ measurements enable a new level of accuracy for assessing polymorphic transformations in Ga2O3 .