Upconversion under Photon Trapping in ZnO/BN Nanoarray: An Ultrahigh Responsivity Solar-Blind Photodetecting Paper

Solar-blind photodetectors (PDs) are widely applicable in special, military, medical, environmental, and commercial fields. However, high performance and flexible PD for deep ultraviolet (UV) range is still a challenge. Here, it is demonstrated that an upconversion of photon absorption beyond the energy bandgap is achieved in the ZnO nanoarray/h-BN heterostructure, which enables the ultrahigh responsivity of a solar-blind photodetecting paper. The direct growth of ultralong ZnO nanoarray on polycrystalline copper paper induced by h-BN 2D interlayer is obtained. Meanwhile, strong photon trapping takes place within the ZnO nanoarray forest through the cyclic state transition of surface oxygen ions, resulting in an extremely high absorption efficiency (> 99.5%). A flexible photodetecting paper is fabricated for switchable detections between near UV and deep UV signals by critical external bias. The device shows robust reliability, ultrahigh responsivity up to 700 A W-1 @ 265-276 nm, and high photoconductive gain of approximate to 2 x 10(3). A negative differential resistance effect is revealed for driving the rapid transfer of up-converted electrons between adjacent energy valleys (Gamma to A) above the critical bias (3.9 V). The discovered rationale and device structure are expected to bring high-efficiency deep UV detecting and future wearable applications.

Automated summary

This study demonstrates the phenomenon of upconversion of photon absorption in the ZnO nanoarray/h-BN heterostructure, achieving ultrahigh responsivity in a solar-blind photodetecting paper. The ultralong ZnO nanoarray is directly grown on polycrystalline copper paper induced by h-BN 2D interlayer. Strong photon trapping occurs within the ZnO nanoarray forest through surface oxygen ion cyclic state transition, resulting in extremely high absorption efficiency.