Silicon p-i-n diodes with different i-region widths are fabricated and tested.It is found that the current shows the non-monotonic behavior as a function of i-region width at a bias voltage of 1.0 V.In this paper,an analytical model is presented to explain the non-monotonic behavior,which mainly takes into account the diffusion current and recombination current contributing to the total current.The calculation results indicate that the concentration ratio of p-region to n-regionplays a crucial role in the non-monotonic behavior,and the carrier lifetime also has a great influence on this abnormal phenomenon.