Ga₂O₃ MISM photodiode arrays with an HfO₂ insulator achieving a 20 fA dark current for solar-blind imaging

Traditional Ga₂O₃ metal-semiconductor-metal (MSM) photodetectors suffer from high dark current, limiting their sensitivity for deep ultraviolet (DUV) imaging. This Letter reports a novel, to the best of our knowledge, metal-insulator-semiconductor-metal (MISM) photon-controlled diode with an ultrathin HfO₂ insulator. The device achieves an ultralow dark current of ~20 fA at 5 V, representing a two-order-of-magnitude reduction compared to conventional MSM counterparts. The MISM structure exhibits exceptional performance metrics: responsivity of 2188 A/W, noise equivalent power of 1.06 × 10^-16 W/Hz^1/2, and over 300-fold photo-to-dark current ratio enhancement. The engineered HfO₂ layer serves as a wide-bandgap energy barrier, suppressing electron leakage and passivating surface traps to enhance carrier collection efficiency. A 16 × 16 focal plane array demonstrates superior image contrast and spatial resolution under faint DUV illumination (100 nW/cm²). This MISM architecture offers a scalable approach for next-generation high-sensitivity DUV imaging systems.