A polarization-insensitive plasmonic cavity photodetector is presented using a two-dimensional nanoscale gold cylindrical array as a plasma electrode. The two-dimensional symmetry of the cylinder makes the plasma electrode insensitive to the polarization angle of the incident light. By forming a metal-semiconductor-metal cavity between a subwavelength metal cylinder and a metal reflector, effective enhancement of light absorption in the ultrathin region can be achieved. The optical and electrical responses of the photodetector were calculated using the time-domain finite difference method and the finite element method, and the effects of the geometric parameters on the performance of the gold nanocylinders were analyzed. The results show that after optimizing the parameters, the overall light absorption rate of the device is 94.7%, and the light absorption rate in GaAs semiconductor can reach 81.1%, and the responsivity of the device can reach 0.37 A/W at 5 V bias voltage and 10 mW incident light power. The device exhibits extremely low polarization-dependent characteristics, where changes in polarization angle do not cause changes in absorption in the device semiconductor, and the absorption response can be effectively preserved without changes in the position of the absorption peak when the angle of incidence changes.

Surface-enhanced Raman Scattering (SERS) is a rapid and highly sensitive molecular detection technology. Having a highly sensitive and uniform Raman signal is a necessary factor in spectroscopy. Raman substrate structures often face complex processes and high costs. To achieve high-performance SERS, Au-Ag composite nanostructures were prepared by multilayer Au-Ag alternate deposition, annealing and dealloying technology in this research, the method can be used for large-area preparation and facile preparation process. By annealing at a suitable temperature, a large number of nanopores are distributed on the surface of Au-Ag composite nanostructures, which can be firmly distributed on the surface to provide hot spots. The Finite-difference Time-domain (FDTD) method is used to simulate the electric field distribution, and the results show that the Au-Ag composite nanostructure surface can induce great local field enhancement. The experiment results exhibit excellent uniformity and high sensitivity of the SERS detection. The enhancement factor of the Rhodamine 6G (R6G) molecules detected by SERS substrate reaches 2.4×10⁵, and the Relative Standard Deviation (RSD) is as low as 6.9%. The minimum detection concentration of R6G molecules by the Au-Ag composite nanostructures can reach 10⁻¹¹ mol/L. The proposed Au-Ag composite nanostructures and the fabrication process have great potential in preparation of high sensitivity and excellent uniformity SERS substrate.