2D transition metal dichalcogenides are promising candidates for high‐performance photodetectors. However, the relatively low response speed as well as the complex transfer process hinders their wide applications. Herein, for the first time, the fabrication of a few‐layer MoTe2/Si 2D–3D vertical heterojunction for high‐speed and broadband photodiodes by a pulsed laser deposition technique is reported. Owing to the high junction quality, ultrathin MoTe2 film thickness, and unique vertical n–n heterojunction structure, the photodiode exhibits excellent device performance in terms of a high responsivity of 0.19 A W−1 and a large detectivity of 6.8 × 1013 Jones. The device is also capable of detecting a broadband light with wavelength spanning from 300 to 1800 nm. More importantly, the device possesses an ultrahigh response speed up to 150 ns with a 3‐dB electrical bandwidth approaching 0.12 GHz. This work paves the way toward the fabrication of novel 2D–3D heterojunctions for high‐performance, ultrafast photodetectors.

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Bi nanoparticles are grown on BiOCl nanosheets via an in situ chemical reduction in a KBH 4 aqueous solution.Bi/BiOCl nanosheets with different contents of Bi nanoparticles can be achieved by changing the concentration of the KBH 4 solution. The structure, morphology, elemental composition and optical absorption performance are characterized using an X-ray diffraction diffractometer, a scanning electron microscope, a high resolution transmission electron microscope, an X-ray photoelectron spectrometer and a UV-Vis diffuse reflection spectrometer. The photocatalytic activities of the as-prepared photocatalysts are tested using the degradation of methyl orange under both UV light and visible light irradiation. Bi nanoparticles modified on BiOCl nanosheets not only enhance the photocatalytic activity under UV light irradiation, but also achieve visible light photocatalytic activity. The mechanism of the photocatalytic processes, such as optical absorption, charge transfer and surface reactions, for the Bi/BiOCl nanosheets are discussed in detail.