Optimization of oxygen flow rate toward high-quality ε-Ga2O3 thin films grown on sapphire substrates and solar-blind ultraviolet photodetectors

Orthorhombic phase ε-Ga₂O₃ is crucial for the fabrication of high-sensitivity solar-blind ultraviolet (UV) photodetectors due to its ultra-wide bandgap. However, the narrow growth window of pure-phase ε-Ga₂O₃ and unclear exploration of growth parameters, such as oxygen flow and temperature, make it challenging to prepare high-performance solar-blind photodetectors. In this study, we use mist chemical vapor deposition technique (mist-CVD) to fabricate high-quality pure-phase ε-Ga₂O₃ thin films on c-plane sapphire substrates. The metal-semiconductor-metal (MSM) solar-blind photodetectors fabricated on ε-Ga₂O₃ thin films exhibiting excellent performance. Firstly, temperature optimization revealed a pure crystalline phase window between 540 °C and 640 °C, with films grown at 580 °C exhibiting the best crystalline quality. Subsequently, at 580 °C, regulating the oxygen flow rate reduced the full width at half maximum (FWHM) of the (002) rocking curve from 0.59° to 0.46°, indicating increased crystallinity due to compensation of oxygen vacancies (Vo). The root-mean-square (RMS) roughness of the ε-Ga₂O₃ thin film is as low as 3.31 nm. Based on the optimized films, high-performance MSM solar-blind photodetectors were fabricated, exhibiting a dark current as low as 2.11 × 10⁻¹¹ A, a responsivity as high as 4.53 A/W, and a detectivity of 8.73 × 10¹³ Jones. This work establishes a systematic framework for the oxygen flow optimization in devices performance and proposes a Vo mechanism to explain this phenomenon, providing valuable insights for fabricating ε-Ga₂O₃ thin films and achieving high-performance solar-blind detection applications.