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

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 x 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 x 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 (R-310/R-400) 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.

Automated summary

In this work, pine-branch-like photodetectors based on SnO2/ZnO heterostructure are fabricated, showing significantly reduced dark current and ultrahigh on/off ratio, which hold great promise for application in visible-blind image sensors.