SPICE Model of SPAD Transient Intrinsic Response Validated using Mixed-Mode TCAD Simulations

This work presents a SPICE compact macro-model for the transient intrinsic response of a Single-Photon Avalanche Diode (SPAD) pixel to a light pulse. The physical phenomena and related parameters are evaluated by performing mixed-mode TCAD simulations. The model is composed of three equivalent diode sub-circuits with their respective junction capacitance adapted to describe the successive mechanisms conditioning the intrinsic transient photo-response of the SPAD. After considering a light pulse, the SPICE model fairly reproduces the TCAD fast current pulse with a peak of about 2mA and a time constant of about 3ps, followed by a diffusion current response with a time constant of 35ps. It results in a self-sustaining current of about 8µA with a diode cathode voltage of 6.3V. Finally, it models the slow recharge through the quenching resistor with a time constant of 264ns. The proposed model facilitates the design of a compatible read-out circuit, e.g., with active recharge, by accurately reproducing physical current and voltage responses.