Highly Sensitive and Tunable Self-Powered UV Photodetectors Driven Jointly by p-n Junction and Ferroelectric Polarization

Ferroelectric (FE) materials are thought to be promising materials for self-powered ultraviolet (UV) photodetector applications because of their photovoltaic effects. However, FE-based photodetectors exhibited poor performance because of the weak photovoltaic effect of FE depolarization field (E_dp) on the separation of photo-generated carriers. In this work, self-powered photodetectors based on both E_dp and built-in electric field at the p-n junction (E_p-n) were designed to obtain enhanced device performance. A NiO/Pb_0.95La_0.05Zr_0.54Ti_0.46O₃ (PLZT) heterojunction-based device is constructed to take advantage of energy level alignments that favor electron extraction. The device exhibits a tunable performance upon varying the polarization direction of PLZT. The NiO/PLZT heterojunction-based device with the PLZT layer in the poling down state shows a higher responsivity [R = (1.8 ± 0.12) × 10^-4 A/W] and detectivity [D* = (3.69 ± 0.2) × 10⁹ Jones], a faster response speed (τ_r = 0.34 ± 0.03 s, τ_d = 0.36 ± 0.02 s), and a lower dark current [I_dark = (1.3 ± 0.19) × 10^-12 A] under zero bias than the PLZT-based device because of the synergistic effects of E_dp and E_p-n. Moreover, under weak-light illumination (0.1 mW/cm²), it exhibits even higher R [(6.3 ± 1.2) × 10^-4 A/W] and D* [(1.29 ± 0.26) × 10¹⁰ Jones] values, which surpass those of most previously reported FE-based self-powered photodetectors. Our work emphasizes the role of the coupling effect between E_p-n and E_dp in the photovoltaic process of NiO/PLZT heterojunction-based devices and provides an effective way to promote the self-powered UV photodetector applications.