Research on the leakage current at sidewall of mesa Ge/Si avalanche photodiode

The effects of surface defects at the sidewall of absorption and multiplication layers on the sidewall leakage current in separate-absorption-charge-multiplication Ge/Si avalanche photodiodes with a mesa structure are investigated. It is found that high-density surface defects and a strong electric field at the sidewall are the reasons for the large sidewall leakage current. In addition, the influence of the width of the guard ring on the sidewall leakage current is also studied. It is found that increasing the width of the guard ring is beneficial to the reduction of the sidewall leakage current by reducing the sidewall electric field and the reduction is not significant when the guard-ring width is greater than 2 µm.