Growth of Metastable α-Ga<sub>2</sub>O<sub>3</sub> Epitaxial Thin Film on Flexible Synthetic Mica by Insertion α-Fe<sub>2</sub>O<sub>3</sub> Buffer Layer

Metastable α-Ga2O3 thin films with a corundum structure were grown epitaxially on flexible synthetic mica. The κ-Ga2O3 thin films were grown in a temperature range of 450‒600 °C, without a buffer layer. In contrast, the α-Ga2O3 thin films were grown in a wider temperature range of 350‒600 °C, by inserting corundum-structured α-Fe2O3 buffer layers. X-ray diffraction (XRD) rocking curve measurements revealed that the α-Ga2O3 thin film grown at 425 °C had the highest degree of crystallinity. Cross-sectional transmission electron microscopy (TEM) observations and an XRD φ scan revealed that the epitaxial relationship between the thin film and the substrate via the buffer layer was (0001) α-Ga2O3 [11‒20] || (001) synthetic mica [100]. Furthermore, when TEM observation was performed close to the surface of the α-Ga2O3 thin film at a high magnification, a lattice image derived from the out-of-plane (0001)-plane orientation was observed. However, it was also revealed that the α-Ga2O3 thin films did not have a single crystal structure but rather an in-plane domain structure. By conducting selected area electron diffraction (SAED) at the interface area, it was determined that the α-Fe2O3 buffer layer was polycrystalline. This implies that α-Ga2O3 thin films were epitaxially grown while forming the in-plane domains on the polycrystalline buffer layers. The results of this study indicate the flexible applications of α-Ga2O3 thin films, which have significant potential for use as power sources and deep-ultraviolet devices.