Ferroelectric Depolarization-Field-Enhanced Ag/ZnO/Si:Ga2O3/BFMO/FTO Multijunction Self-Driven Photodetector with Ultrahigh Performance

We demonstrate herein a novel ferroelectric depolarization-field (E_dp)-enhanced Ag/ZnO/Si:Ga₂O₃/BFMO/FTO multijunction photodetector, which delivers ultrahigh self-driven detection performance in terms of responsivity (R) and detectivity (D*) toward ultraviolet (UV) band (200–300 nm) signals. Owing to the superposition of various interfacial electric fields (i.e., E_ZnO/Si:Ga2O3, E_{Si:Ga2O3/BFMO}, and E_BFMO/FTO), the unpoled Ag/ZnO/Si:Ga₂O₃/BFMO/FTO multijunction device exhibits much higher R (46.6 mA/W) and D* (1.02 × 10¹² Jones) than the Ag/Si:Ga₂O₃/BFMO/FTO dual-junction device (R = 25.3 mA/W; D* = 6.20 × 10¹¹ Jones) and the Ag/Si:Ga₂O₃/FTO single-junction device (R = 12.5 mA/W; D* = 3.33 × 10¹¹ Jones). Moreover, the Ag/ZnO/Si:Ga₂O₃/BFMO/FTO device, when upward poled, shows 9 and 9.8% further enhancement in R (50.8 mA/W) and D* (1.12 × 10¹² Jones), respectively, compared to the unpoled state. The device exhibits short rise/decay (τ_r/τ_d) response times of 4.4/17.3 ms due to the multiple electric-field-derived rapid separation of photogenerated carriers. The device shows even higher photodetection performance with an R of 103.9 mA/W and a D* of 2.29 × 10¹² Jones under weak light illumination (P_260 nm = 0.001 mW/cm²). These parameters surpass those of the most previously reported Ga₂O₃-based self-driven photodetectors. The present work indicates that the strategy of introducing multiple built-in electric fields to synergistically separate photogenerated carriers offers an effective approach for the development of high-performance optoelectronic devices including Ga₂O₃-based self-driven photodetectors.