Optical Activity and Phase Transformations in γ/β Ga₂O₃ Bilayers Under Annealing

Abstract Gallium oxide (Ga₂O₃) can be crystallized in several polymorphs exhibiting different physical properties. In this work, polymorphic structures consisting of the cubic defective spinel (γ) film on the top of the monoclinic (β) substrate are fabricated by disorder‐induced ordering, known to be a practical way to stack these polymorphs together. Such bilayer structures are annealed to investigate optical properties and phase transformations. Specifically, photoluminescence and diffuse reflectance spectroscopy are combined with transmission electron microscopy, Rutherford backscattering/channeling spectrometry and X‐ray diffraction to monitor the evolutions. As a result, a two‐stage annealing kinetics is observed in γ/β Ga₂O₃ bilayers associated with the epitaxial γ‐to‐β regrowth at the interface at temperatures below 700 °C and a non‐planar γ‐to‐β phase transformation starting at higher temperatures. Thus, the present data enhance understanding of the polymorphism in Ga₂O₃, interconnecting the phase transformation kinetics with the evolution of the optical properties.