Simple ( <scp>YG</scp> a) ₂ <scp>O</scp> ₃ /F‐ <scp>S</scp> n <scp>O</scp> ₂ Heterojunction‐Based Solar‐Blind Ultraviolet Photodetector Operable in Two Modes With Superb Performance

Gallium oxide (Ga 2 O 3 ), with its wide direct bandgap (~4.9 eV) and high stability, holds great potential for applications in solar‐blind ultraviolet (SBUV) photodetectors. In this work, simple vertical‐structured SBUV photodetectors based on (YGa) 2 O 3 /F‐SnO 2 (YGO/FTO) heterojunctions were designed and fabricated for the first time. Owing to the wider bandgap of Y 2 O 3 (~5.9 eV) compared to Ga 2 O 3 and the stronger Y–O bonding relative to Ga–O, the YGO alloy films exhibit an expanded bandgap (~5.2 eV) with fewer oxygen vacancies than pure Ga 2 O 3 . This results in SBUV photodetectors with an extremely low dark current and fast photoresponse. Moreover, the YGO/FTO‐based photodetectors demonstrate excellent performance in both biased and self‐driven modes. At 0 V bias, the photodetector with a YGO layer thickness of 246 nm exhibits an exceptionally low dark current of 0.145 pA, a short photoresponse time of 15 ms, high responsivity of 12.2 mA W −1 , and a detectivity of 2.84 × 10 12 Jones. At a bias of −10 V, the device with a 425 nm‐thick YGO layer achieves a high photocurrent/dark current ( I photo / I dark ) ratio of 10 6 , UV/visible rejection ratio of 10 5 , and remarkably high responsivity of 12.3 A W −1 with a detectivity of 1.08 × 10 15 Jones. These results highlight the great promise of YGO alloys in developing simple vertical‐structured YGO/FTO high‐performance photodetectors for ultraweak SBUV detection.