Fig. 1. (Color online) (a) TiO₂@GaO_xN_y-Ag heterojunction preparation process. SEM image of (b) FTO, (c) TiO₂, (d) TiO₂@GaO_xN_y and (e) TiO₂@GaO_xN_y-Ag. (f) The TEM image of TiO₂@GaO_xN_y-Ag. (g) corresponds to the HRTEM image of TiO₂ in Fig. 1(f). (h) corresponds to the GaN and GaO_xN_y in the ʻeʼ, ʻfʼ, and ʻgʼ regions in Fig. 1(f). (i) corresponds to the HRTEM image of the Ag nanoparticle.

Fig. 2. (Color online) (a) XPS survey spectrum. High-resolution spectra of (b) Ga 3d, (c) O 1s, (d) N 1s and (e) Ag 3d. (f) The O 1s peak and inelastic scattering loss for TiO₂@GaO_xN_y-Ag heterojunction.

Fig. 3. (Color online) (a) The schematic of the structure of the TiO₂@GaO_xN_y-Ag photodetector. (b) The optical image of the fabricated photodetector. (c) Photocurrent change relationship of TiO₂, TiO₂@GaO_xN_y, and TiO₂@GaO_xN_y-Ag devices at various wavelengths; the bias voltage is 1 V, the optical power density is 5.0 mW/cm². (d) TiO₂@GaO_xN_y-Ag photocurrent change graph at 380, 480, and 580 nm wavelengths, bias voltage of -1 V to 1 V, optical power density of 5.0 mW/cm². (e) The current-time relationship diagram of the switch state under the aforementioned test conditions. (f)–(h) Light response time test diagrams at various wavelengths under the aforementioned test conditions. (i) Comparison of TiO₂@GaO_xN_y-Ag photodetector’s performance in comparison to the reported TiO₂ and Ga₂O₃ heterojunction-based photodetector in the literature.

Fig. 4. (Color online) (a) UV-Vis absorption spectrum. (b) The relationship between (αhν)² and (hν). (c) Projected electronic density of states for the TiO₂@GaO_xN_y structure with the Fermi energy set to 0 eV.

Fig. 5. (Color online) (a) Schematic illustration of the FDTD simulation setup used for the extinction power calculation and local electric field distribution of the TiO₂@GaO_xN_y-Ag heterojunction. (b) Calculated extinction power for the pure TiO₂, TiO₂@GaO_xN_y, and TiO₂@GaO_xN_y-Ag. The electric field distributions corresponding to the FDTD simulation of the TiO₂@GaO_xN_y-Ag heterojunction under different wavelengths of illumination (c) 380 nm; (d) 480 nm; (e) 580 nm.

Fig. 6. (Color online) (a) Schematic band diagram of TiO₂@GaO_xN_y-Ag demonstrating the behaviour of charge transport. (b) The energy band diagram illustrating the transport properties of the TiO₂@GaO_xN_y-Ag heterojunction.