CMOS-based Ge-on-Si SPAD featuring a modified Ge structure for ultra-low-noise performance

SWIR detection applications have recently attracted significant attention, particularly for high-sensitivity photodetectors compatible with CMOS technology. In this work, we propose and simulate a modified charge-focusing structure integrated with a SACM SPAD based on TSMC's 0.18 μm HV CMOS technology. Benefiting from the charge-focusing mechanism in combination with the SACM architecture, the higher doping concentration in the Ge layer and a reduced doping concentration in the charge sheet layer significantly suppresses avalanche current at the corners and edges of the Ge trench and mitigates excess current flowing through the Ge region. These enhancements contribute to a lower probability of afterpulsing and reduced leakage current.