In this study the responsivity and quantum efficiency of p-Si/i-β-FeSi2/n-Si double-heterostructure photodiodes and p-Si/i-Si/n-Si photodiodes are investigated by self-developed analytical methods. The dark current densities of both β-FeSi2 and Si p–i–n photodiodes under the reverse bias condition are calculated by solving the diffusion current densities of minority carriers. The photocurrent densities of both p–i–n photodiodes under illumination with reverse bias are mainly calculated by solving the drift current densities in the depletion regions. When the β-FeSi2 p–i–n photodiode incident wavelength, λ, is less than 0.6 µm, the magnitudes of responsivity and quantum efficiency are almost zero for different intrinsic thicknesses. The maximum responsivity, R = 0.65 A/W, and quantum efficiency, η = 65%, are both at λ = 1.2 µm and the intrinsic β-FeSi2 layer thickness is 100 µm. The calculated responsivity of the Si p–i–n photodiode is consistent with the reported studies. Therefore, the analysis methods and results are valid in this work. These results indicate the high applicability of β-FeSi2 to near-infrared photodiodes integrated with Si. Therefore, the p-Si/i-β-FeSi2/n-Si photodiode is a new high-efficiency light sensor device applicable to optical fiber communications.