Photodetection properties of populated Fe3O4@TiO2 core–shell/Si heterojunction prepared by laser ablation in water

In this work, we demonstrated the first study on the preparation and characterization of the populated Fe3O4@TiO2 core–shell/Si photodetector by laser ablation in liquid. The structural and optical properties of Fe3O4 nanoparticles and Fe3O4@TiO2 core–shell nanoparticles were studied by X-ray diffraction, transmission electron microscope, and UV–Vis absorption. X-ray diffraction findings suggest the formation of a populated crystalline Fe3O4@TiO2 core–shell through the existence of XRD peaks related to TiO2 and Fe3O4. The optical properties revealed that the optical energy gap of Fe3O4@TiO2 was 3 eV, while the optical energy gap of Fe3O4 was 2.8 eV. Raman studies reveal the presence of vibration modes centered at 91 cm−1 (Eg), 144 cm−1 (Eg), 396 cm−1 (B1g), 512 cm−1 (B1g), 541 cm−1 (B1g + A1g), and 609 cm−1 (Eg) which are belong to the TiO2. The vibration modes related to the magnetite Fe3O4 are observed at 145–1 (T2g), 302 cm−1 (T2g), and 554 cm−1 (T1g). Transmission electron microscope results suggest the presence of a core–shell morphology with an average size of 60 nm. The current–voltage characteristics of Fe3O4/p-Si and Fe3O4@TiO2 core–shell/p-Si photodetectors are measured in the dark and under illumination conditions. The maximum responsivity of the Fe3O4@TiO2/Si photodetector was 0.5A/W at 400 nm, while the maximum responsivity of Fe3O4/p-Si photodetector was 0.4A/W at 500 nm. The specific detectivity and external quantum efficiency of the Fe3O4@TiO2/p-Si photodetector are larger than those of Fe3O4/p-Si photodetector.