Silicon materials are widely used in the field of photoelectric detection because of their excellent optoelectronic properties. Theoretically, the long wave response limit of intrinsic silicon is about 1100 nm. However, it is found in experiments that silicon-based devices will also produce out-of-band response output under the irradiation of 1319 nm laser, which indicates that the photoelectric response characteristics of silicon materials deviate from the theoretical situation, which will cause significant interference to high-precision detection. The out-of-band responses of silicon-based devices indicate that the energy band structure of silicon materials has changed. Since intrinsic point defects can change the energy levels of silicon materials, it is necessary to study the effects of intrinsic point defects in different states on the photoelectric response characteristics of silicon materials. The theoretical analysis results can provide a reference for the subsequent application and development of silicon-based optoelectronic devices in the field of high-precision detection.

The intrinsic point defects in single crystal silicon can change the band structures of silicon materials, thereby affecting the quality of materials and the performance of devices. Therefore, according to the intrinsic point defects of vacancies and self-interstitial atoms in single crystal silicon, cell models with defects in different states are established based on the first principles. The influence of intrinsic point defects on the band structure of silicon materials and the change in the optical properties of silicon materials under the influence of defects are analyzed. On this basis, the response output characteristics of silicon materials with intrinsic point defects under the irradiation of 532 nm and 1319 nm are calculated.

The vacancy defects and self-interstitial atomic defects in different states will introduce defect energy levels into the energy level distribution of silicon, leading to the decrease or even disappearance of the band gap of silicon materials. These intrinsic point defects make the density of states move towards the low-energy direction as a whole (Fig. 2) and mainly affect the value of the density of states near the Fermi level, indicating that the number of energy levels within the energy range near the Fermi level increases significantly. Among several typical point defect states, the out-of-band response of silicon is mainly due to the influence of the tetrahedral interstitial defect. Under the irradiation of 1319 nm, the intrinsic silicon hardly absorbs photons, but the tetrahedral interstitial defect makes the absorption coefficient of silicon material as high as 50391 cm^-1 [Fig. 3(b)], and the quantum efficiency increases to 0.2901 [Fig. 5(b)]. Thus, the silicon material can produce a strong response output to the irradiation of 1319 nm laser, making the output saturation threshold of the silicon-based photosensitive unit the minimum in several defect states, which is 0.0015 W·cm^-2 [Fig. 7(b)].

For the intrinsic point defects inherent in silicon materials like vacancies and self-interstitial atoms, cell models with defects in different states are established based on the first principles, and the effects of different types of vacancy defects and self-interstitial atomic defects on the energy level structure of silicon materials are analyzed. The response output characteristics of silicon materials under the irradiation of 532 nm and 1319 nm lasers are calculated in detail, and the effects of different vacancies and self-interstitial atomic defects on the actual output are compared. The results show that both vacancy defects and self-interstitial atomic defects will introduce defect levels into the band gap, thus changing the band structure of silicon materials and enhancing the response of silicon in visible and infrared bands. For the in-band laser of 532 nm, the saturation thresholds of the silicon-based photosensitive unit decrease to different degrees under the effects of different states of intrinsic point defects. For the out-of-band laser of 1319 nm which does not respond theoretically, the properties of silicon materials affected by the tetrahedral interstitial defect have the most obvious changes under the same concentration. In other words, the out-of-band response of silicon materials under the irradiation of 1319 nm laser is mainly caused by tetrahedral interstitial defects present in silicon. In this case, the Fermi energy level enters into the conduction band, making the band gap of silicon disappear. The absorption coefficient reaches 50391 cm^-1, and the refractive index decreases by 25.99% compared with the intrinsic silicon, making the quantum efficiency increase to 0.2901. Therefore, the silicon material can produce a strong response at this wavelength, resulting in a low output saturation threshold of 0.0015 W·cm^-2. The theoretical analysis results can provide a reference for the subsequent application and development of silicon-based optoelectronic devices in the field of high-precision detection.