Hot electron photodetectors (HEPDs) with wide spectrum responses are promising in the fields of image sensors and optical communications, etc. Metallic micro/nano-structures can efficiently generate hot carriers by exciting surface plasmons. It is helpful to realize low-cost and wide-spectrum response photodetectors when the heterostructures form by combining metallic micro/nano-structures with wide bandgap semiconductors. This approach can also be applied to improve the performance of HEPDs made of other semiconductors. This work contributes to the development of advanced plasmonic devices.During the fabrication, the wet-cleaned FTO glass substrates were first subjected to the surface plasma treatment for increasing the work function of FTO substrates. Then, TiO₂and Au films were prepared by radio frequency (RF) and direct current (DC) magnetron sputtering, respectively. In detail, a TiO₂ layer with a thickness of 20 nm was deposited onto the FTO substrate, followed by the deposition of an ultrathin Au film with its thickness varying from 2 nm to 8 nm. Then, the as-prepared multiplayer samples were annealed in air at 500 °C. The annealing process could, simultaneously, transform the ultrathin Au film into a layer of Au NPs, and transform the amorphous TiO₂ film into its polycrystalline anatase film structure with a rough profile. After that, another thin Au film was deposited onto the annealed samples by DC magnetron sputtering. Here, the thin Au film can act as the transparent electrode with its thickness fixed to 20 nm. The proposed hybrid plasmonic nanostructure based HEPD has an architecture as shown in Figure 1. Here, the TiO₂ layer formed a concave-convex nanostructure with a scale of about 100 nm after annealing process, the nanostructure constructed by the Au nanoparticle layer and the conformal Au film used as electrode is for exciting surface plasmons. With the assistance of the Au/TiO₂ composite nanostructure, the device has a wide spectrum absorption in the range of 400 nm to 900 nm, and the average absorption efficiency is 33.84%. Therefore, the proposed device can detect the incident photons outside the intrinsic absorption band of TiO₂. The responsivity and linear dynamic range of the device under the wavelength of 600 nm separately are 9.67 μA/W and 60 dB (Fig.2). Besides, the corresponding rise/fall response speed are 1.6 ms and 1.5 ms respectively. (Fig.3). The finite element method is also used for simulation calculation, and the electric field distribution diagrams verify that the rich surface plasmon resonances excited in the Au/TiO₂ composite nanostructure, which is the reason for realizing the wide spectrum and high efficiency detection (Fig.5). In summary, we demonstrated a TiO₂-based HEPD by incorporating a hybrid plasmonic nanostructure made of Au NPs together with a conformal Au film. Different from other similar approaches that were designed for high-efficiency hydrogen generation in the photocatalysts, a hybrid plasma nanostructure was used in photodetectors for realizing wide spectrum response. With the structural diversity of the hybrid plasmonic nanostructure, different surface plasmon resonances were excited, so that the device can respond to incident photons in a broadband wavelength range, covering UV-visible-NIR. The method of constructing hybrid plasmonic nanostructures has a guidance in developing high-performance optoelectronic devices.