A Review of ε-Ga₂O₃ Films: Fabrications and Photoelectric Properties

Gallium oxide (Ga₂O₃), as an ultra-wide bandgap semiconducting material, has attracted extensive research interest in recent years. Owing to its outstanding electrical and optical properties, as well as its high reliability, Ga₂O₃ shows great potential in power electronics, optoelectronics, memory devices, and so on. Among all the different polymorphs, ε-Ga₂O₃ is the second most thermally stable phase. It has a hexagonal crystal structure, which contributes to its isotropic physical properties and its suitable growth on low-cost commercial substrates, such as Al₂O₃, Si (111). However, there are far fewer research works on ε-Ga₂O₃ in comparison with the most thermally stable β phase. Aiming to provide a comprehensive view on the current works of ε-Ga₂O₃ and support future research, this review conducts detailed summarizations for the fabrication processes of ε-Ga₂O₃ thin films and the photoelectrical properties of ε-Ga₂O₃-based photodetectors. The effects of different deposition parameters on film phases and qualities are discussed. The forming mechanisms of ε phase prepared by chemical vapor depositions (CVDs) and physical vapor depositions (PVDs) are analyzed, respectively. Conclusions are made concerning the relationships between film microstructures and properties. In addition, strategies for further improving ε-Ga₂O₃ film performance are briefly summarized.