The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes(PDs) was studied.Due to a two-step growth method,there are high defect densities in low-temperature buffer Ge layer.It is shown that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field,leading to the increase of the total dark current for p-Ge/i-Ge/n-Si PDs,whereas these defects have no influence on the dark current for n-Ge/i-Ge/p-Ge PDs.As a complement,a three-dimensional simulation of the total current under illumination was also performed. The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge / i-Ge / n-Si and n-Ge / i-Ge / p-Ge photodiodes (PDs) was studied. Due to a two-step growth method, there are high defect densities in low-temperature buffer Ge layer. It shows that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field, leading to the increase of the total dark current for p- Ge / i-Ge / n-Si PDs, these these have no influence on the dark current for n-Ge / i-Ge / p-Ge PDs. A complement, a three- dimensional simulation of the total current under illumination was also performed.