Silicon based optoelectronics are compatible with CMOS technology, and with the help of mature microelectronic processing platforms, large-scale mass production can be achieved. It has the advantages of low cost, high integration, and high reliability. Among them, the application of silicon based semiconductor detectors in the visible light band has become more mature. However, the commonly used semiconductor materials for near-infrared band detectors have drawbacks such as difficulties in compatibility with existing CMOS processes and high prices. Therefore, expanding the operating frequency range of silicon based semiconductor detectors to the near-infrared band is of great significance. Due to the bandgap width of silicon, there are significant limitations in the absorption of electromagnetic waves by silicon based materials in the near-infrared band, posing serious challenges for the application of silicon based detectors in the near-infrared band.In order to break through the bandgap width limitation of silicon and improve the absorption performance of silicon materials in the near-infrared band, a silicon based structure based on gradient doping of nanometallic particles was proposed, based on the near-field enhancement effect generated by local surface plasmon resonance of nanometallic particles. The slow change in doping concentration can effectively solve the severe change in reflectivity caused by refractive index mutation. By applying the Maxwell Garnett equivalent medium theory, the absorption characteristics of composite silicon based structures in the visible and near-infrared bands were simulated, and the effects of two doping concentration changes and two doping metals on the absorption enhancement effect of silicon based materials were compared. The results indicate that the structure has a significant improvement in electromagnetic wave absorption in the near-infrared band. When the doped metal is silver, both decreasing and increasing doping can bring absorption improvement in the 640-1080 nm wavelength range. However, increasing doping can avoid the drastic change in reflectivity caused by refractive index mutations, and its effect is significantly better than decreasing doping(Fig.6). When comparing the effects of different metals, the absorption enhancement band brought by the doping of gold nanoparticles is wider than that of silver nanoparticles. So when choosing gradient increasing doping of gold nanoparticles, the effect is optimal, and the absorption performance can be improved in the 610-1450 nm wavelength range, with a maximum improvement of 10.7 dB(Fig.7).A silicon based structure that can break through the bandgap width limitation of silicon was proposed, near-infrared absorption enhancement was achieved, and the absorption enhancement effect under different conditions was simulated and analyzed. The proposed structure can effectively enhance the absorption efficiency of silicon based materials in the near-infrared band, which helps to improve the performance of silicon based devices. And by comparing different doping methods and metal selection, it is concluded that gradient increasing doping of gold nanoparticles is the optimal choice. The research results of this article provide important references for the application of silicon based semiconductor detectors in the near-infrared band.