Pine‐Branch‐Like SnO₂/ZnO Heterostructure with Suppressed Dark Current and Enhanced On/Off Ratio for Visible‐Blind UV Imaging

Abstract In general, wide bandgap semiconductors (Eg > 3.0 eV) are sensitive to visible‐blind ultraviolet (UV) radiation. However, a large dark current makes it difficult to implement efficient visible‐blind sensing, which impedes their application in visible‐blind UV image. In this work, pine‐branch‐like photodetectors (PDs) based on SnO₂/ZnO heterostructure are successfully fabricated. Compared with the high dark current (1.5 × 10^‐8 A) and low on/off ratio (42) of SnO₂ PD, the designed SnO₂/ZnO/4 (S/Z/4) PD shows a significantly reduced dark current (1.3 × 10^‐12 A), ultrahigh on/off ratio (16 405) under 300 nm UV illumination at 1 V bias. In addition, the UV/visible rejection ratio (R₃₁₀/R₄₀₀) of S/Z/4 PD is 1193, which is almost 48‐times of that of SnO₂ PD (25). This shows great promise for application in visible‐blind image sensors. The enhancement in performance is attributed to the formation of the type‐II energy band structure, the low conductivity of ZnO layer, and the light trapping effect of pine‐branch‐like structure. Moreover, the SnO₂/ZnO/4 PD also exhibits fast response speed with a rising time of 0.48 ms and decay time of 2.07 ms, which exceeds most of the metal oxide‐based PDs. The fabrication approach of pine‐branch‐like heterojunction can be extended to other one‐dimensional materials for high‐performance optoelectronic devices.