Enhancing Performance of Ultraviolet C Photodetectors Through Single‐Domain Epitaxy of Monoclinic β‐Ga₂O₃ Films and Tailored Anti‐Reflection Coating

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga₂ O₃ films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga₂ O₃ films on a hexagonal sapphire substrate. Unlike 3D β-Ga₂ O₃ films with twin domains, 2D β-Ga₂ O₃ films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga₂ O₃ films and the application of ARC for the development of high-performance UVC PDs.