Abstract: The Sun serves as the primary source of ultraviolet radiation on Earth. The UVC band, 200–280 nm, is strongly absorbed by atmospheric ozone, thereby establishing a naturally low-background-noise “solar-blind region.” Solar-blind UV photodetectors operating within this spectral range exhibit significant potential in applications such as flame detection, missile early warning systems, and ozone monitoring. With its ultra-wide bandgap of 4.7–4.9 eV, β-Ga₂O₃ has emerged as a highly promising material for the fabrication of such detectors. To further enhance device performance, this study introduces a dual-layer light-trapping architecture that incorporates surface nanopores and a bottom aluminum grating. Simulations conducted using the Finite Difference Time Domain (FDTD) method reveal that this composite structure achieves an absorption efficiency of 63.7% at a wavelength of 250 nm, representing a 247% improvement compared to unstructured devices. Additionally, the device’s responsivity increases from 0.55 A/W to 7.08 A/W, with more than 50% responsivity retained even at incident angles as large as 60°, demonstrating exceptional angular robustness. These simulation results confirm the synergistic interaction between light-scattering enhancement from nanopores and plasmonic resonance in metal gratings, offering a robust theoretical foundation for the design and fabrication of high-performance Ga₂O₃-based solar-blind ultraviolet detectors.