Low-dimensional ultrawide bandgap semiconductors demonstrate great potential in fabricating solar-blind ultraviolet photodetectors. However, the widespread use of detectors is still limited by the low responsivity, large noise, and dark current, and especially few detectors can fulfill the solarblind ultraviolet detection and the polarization dependence simultaneously. Herein, a polarization sensitive solar-blind ultraviolet photodetector based on ultrathin KNb 3 O 8 nanobelts synthesized via chemical vapor deposition growth, is reported. By selecting suitable substrate and tuning the growth temperature, the nonlayered KNb 3 O 8 crystal is grown into the quasi-1D ultrathin nanobelt with thickness in the range of 4.8-120 nm. Density functional theory calculations and experimental results indicate that the ultrathin KNb 3 O 8 nanobelt possesses an ultrawide bandgap (4.15 eV) as well as unusual in-plane structural anisotropy. Benefiting from the above features, the ultrathin KNb 3 O 8 nanobelt-based device exhibits superior photodetection performances with high responsivity (30 A W −1 ), high detectivity (5.95 × 10 11 Jones), and ultralow dark current (7.1 × 10 −15 A) in the solar-blind ultraviolet region (230-280 nm). In addition, the KNb 3 O 8 photodetector displays strong polarization sensitive photoresponse with a linear dichroic ratio of 1.62 at 254 nm. With these remarkable features, the ultrathin KNb 3 O 8 nanobelt provides great opportunities for designing the next-generation multifunctional solar-blind ultraviolet optoelectronic devices.

The intentionally designed band alignment of heterostructures and doping engineering are keys to implement device structure design and device performance optimization. According to the theoretical prediction of several typical materials among the transition metal dichalcogenides (TMDs) and group‐IV metal chalcogenides, MoS2 and SnSe2 present the largest staggered band offset. The large band offset is conducive to the separation of photogenerated carriers, thus MoS2/SnSe2 is a theoretically ideal candidate for fabricating photodetector, which is also verified in the experiment. Furthermore, in order to extend the photoresponse spectrum to solar‐blind ultraviolet (SBUV), doping engineering is adopted to form an additional electron state, which provides an extra carrier transition channel. In this work, pure MoS2/SnSe2 and doped MoS2/SnSe2 heterostructures are both fabricated. In terms of the photoelectric performance evaluation, the rejection ratio R254/R532 of the photodetector based on doped MoS2/SnSe2 is five orders of magnitude higher than that of pure MoS2/SnSe2, while the response time is obviously optimized by 3 orders. The results demonstrate that the combination of band alignment and doping engineering provides a new pathway for constructing SBUV photodetectors.