Ag₂O/β-Ga₂O₃ Heterojunction-Based Self-Powered Solar Blind Photodetector with High Responsivity and Stability

Self-powered deep-ultraviolet photodetectors have received considerable attention in recent years because of their efficiency, reliability, and various applications in civilian and military fields. Herein, a Ag/Ag₂O layer is continuously deposited on a β-Ga₂O₃ epitaxial layer by a facing target sputtering system without opening the chamber, which has an advantage in time and cost. A p-n junction photodetector was constructed through the Ag₂O/β-Ga₂O₃ heterojunction and by varying the thickness of the Ag film, which was controlled by the sputtering time. The effect of top electrode thickness on the photoresponse characteristics of photodetectors was studied. Because thin Ag films have low surface roughness, indicating low optical loss and good interfacial conditions, photodetectors using a thin Ag film as the top electrode exhibit high photoresponsivity. However, Ag films that were thinner than the threshold thickness, which is the minimum thickness required to form a continuous, homogeneous surface film, exhibited rather low performance owing to the high reflection and scattering caused by the inhomogeneous surface morphology. The as-fabricated photodetector with a 20 nm Ag film presents a high on/off ratio of 3.43 × 10⁸, responsivity and detectivity of 25.65 mA/W and 6.10 × 10¹¹ Jones, respectively, and comparable rise and decay times of 108 and 80 ms, respectively. Additionally, even after three months of storage in an ambient environment, the photoresponse of the photodetector was maintained, indicating good stability in air. These results suggest that Ag₂O/β-Ga₂O₃ heterojunction-based photodetectors with thin Ag films can be used in various applications requiring deep-ultraviolet detection without an external power supply.