van der Waals epitaxy of ferroelectric ɛ-gallium oxide thin film on flexible synthetic mica

This study demonstrates the formation of the van der Waals epitaxy of the ɛ-gallium oxide (Ga₂O₃) thin film on cleaved synthetic mica via mist chemical vapor deposition. Orthorhombic ɛ-Ga₂O₃ (001) was epitaxially grown on synthetic mica (001). The analysis using transmission electron microscopy revealed an in-plane orientation of ɛ-Ga₂O₃ [010] ∣∣ synthetic mica [010]. However, the most thermodynamically stable β-Ga₂O₃ was grown at the film-substrate interface. The optical direct bandgap of the ɛ-Ga₂O₃ thin film grown by van der Waals epitaxy was estimated to be 5.0 eV, which was the same as for the heteroepitaxially grown ɛ-Ga₂O₃ thin film on other substrates. Besides, after ɛ-Ga₂O₃ thin film was grown on the synthetic mica substrates that are cleaved sufficiently thin, the sample could be bent or cut with scissors. These results denote that the epitaxial ɛ-Ga₂O₃ thin films grown by van der Waals epitaxy can be applied to flexible electronics.