Effect of oxygen partial pressure on amorphous Ga₂O₃-based solar-blind ultraviolet photodetectors

Solar-blind photodetectors(SBPDs) exhibit advantages such as high sensitivity, high communication accuracy, and high signal-to-noise ratio, making them highly desirable for applications in ozone hole monitoring, corona detection, missile warning, and other military and civil fields. Among the materials utilized for SBPDs, Ga₂O₃ is particularly attractive due to its bandgap that inherently corresponds to a solar-blind spectrum without any alloy and dopant. Generally, crystalline Ga₂O₃ exists in various polymorphs, including α, β, γ, ε, and δ. Among these, β-Ga₂O₃ possesses the most stable structure. Therefore, β-Ga₂O₃ in the form of thin films, nano-structures, and single crystals has been widely explored for detection applications. In 2018, Kanika et al. reported the growth of β-Ga₂O₃ thin films on silicon substrates using a high-temperature seed layer and successfully constructed a solar-blind UV photodetector. The device demonstrated excellent performance under extremely weak ultraviolet signals (44 nW/cm²) with a responsivity of 96.13 AW⁻¹ and an external quantum efficiency of 4.76×10⁴. In 2019, Wang et al. prepared a high-quality β-Ga₂O₃ film on a sapphire substrate via magnetron sputtering followed by post-deposition annealing. Furthermore, a metal-semiconductor-metal(MSM) structure photodetector was successfully prepared. This device exhibited a photo-to-dark current ratio greater than 10³, a response time of 0.31 s, and a decay time of 0.05 s. However, the high-temperature growth conditions required for β-Ga₂O₃ can increase the cost and complexity of the process, potentially hindering its widespread applications.

The amorphous Ga₂O₃ (a-Ga₂O₃), with its uniform structure, is getting popular among researchers worldwide, as it is fabricated through a simple process at low temperatures. As previously reported, a-Ga₂O₃-based photodetectors can obtain performance comparable to that of β-Ga₂O₃ photodetectors. Currently, radio frequency(RF) magnetron sputtering has been widely applied to prepare a-Ga₂O₃ thin films, which has the advantages of a fast growth rate, simplicity of operation, and low cost. However, despite the high responsivity of a-Ga₂O₃ solar-blind photodetectors prepared by RF magnetron sputtering, this high responsivity is often accompanied by a slow response speed. The reason for this is the presence of a large number of oxygen vacancies in the a-Ga₂O₃ films deposited via magnetron sputtering. In this paper, we optimized the oxygen partial pressure during magnetron sputtering to control the concentration of oxygen vacancies in the film. We prepared MSM photodetectors to investigate the effect of different oxygen partial pressures on the performance of the solar-blind photodetectors. The results demonstrate that the oxygen partial pressure can effectively regulate the oxygen vacancies in a-Ga₂O₃ thin films, and an optimized oxygen partial pressure allows the photodetector to achieve a balance between responsivity and response speed.