Design and simulation of a near-infrared enhanced Si-based SPAD for an automotive LiDAR

A near-infrared (NIR)-enhanced single-photon avalanche diode (SPAD) with a retrograded NM/XP junction for an automotive LiDAR was designed based on CSMC 0.18 µm BCD technology. A 3 µm depth NM/XP junction embedded in a lightly doped deep p-well (DP) improves the absorption efficiency in the NIR regime; the photo-generated electrons generated in the depletion region are efficiently collected into the central multiplication region by a drift process, and then the impact ionization is triggered by the strong field, resulting in a high photon detection efficiency (PDE). Additionally, the deep NM/XP junction and the buried layer effectively isolate the dark noise originating from the interface and the substrate. The SPAD was initially simulated by numerical calculation, and then was evaluated with active quench/reset electronics in a circuit simulator. The results revealed that the SPAD with an active area of 314µm ² achieves a PDE of 16.2% at 905 nm and a dark count rate (DCR) of 1.46H z/µm ², with an excess bias of 5 V at room temperature. The designed SPAD is well suited for the low-cost, miniaturized automotive LiDAR.