Ultraviolet photodetectors with high photosensitivity based on type-II ZnS/SnO₂ core/shell heterostructured ribbons

Semiconducting heterostructures with type-II band structure have attracted much attention due to their novel physical properties and wide applications in optoelectronics. Herein, we report, for the first time, a controlled synthesis of type-II ZnS/SnO₂ heterostructured ribbon composed of SnO₂ nanoparticles that uniformly cover the surface of ZnS ribbon via a simple and versatile thermal evaporation approach. Structural analysis indicated that the majority of SnO₂ nanoparticles have an equivalent zone axis, i.e., <-313> of rutile SnO₂, which is perpendicular to ±(2-1-10) facets (top/down surfaces) of ZnS ribbon. For those SnO₂ nanoparticles decorated on ±(01-10) facets (side surfaces) of ZnS ribbon, an epitaxial relationship of (01-10)_ZnO//(020)_SnO2 and [2-1-10]_ZnO//[001]_SnO2 was identified. To explore their electronic and optoelectronic properties, we constructed field-effect transistors from as-prepared new heterostructures, which exhibited an n-type characteristic with an on/off ratio of ∼10³ and a fast carrier mobility of ∼33.2 cm² V^-1 s^-1. Owing to the spatial separation of photogenerated electron-hole pairs from type-II band alignment together with the good contacts between electrodes and ribbon, the resultant photodetector showed excellent photoresponse properties, including large photocurrent, high sensitivity (external quantum efficiency as high as ∼2.4 × 10⁷%), good stability and reproducibility, and relatively fast response speed. Our results suggest great potential of ZnS/SnO₂ heterostructures for efficient UV light sensing, and, more importantly, signify the advantages of type-II semiconducting heterostructures for construction of high-performance nano-photodetectors.