PHYSICS AND NUMERICAL-SIMULATION OF SINGLE-PHOTON AVALANCHE-DIODES

We present results of the numerical simulation of the transient behavi or of shallow junction single photon avalanche diodes (SPAD's). We dev eloped a bidimensional model for above breakdown simulations and show that the initially photogenerated charge density builds up locally by an avalanche multiplication process and then spreads over the entire d etector area by a diffusion-assisted process. To model real geometries , we developed a simplified model based on the obtained results. The i mportance of the photon-assisted spreading mechanism is evaluated and compared with the diffusive one. The contribution of the photon-assist ed mechanism is minor in these geometries. The model is compared with the experimental data on the avalanche leading edge and the timing res olution; the agreement is good. We conclude that the model can be cons idered to be a useful tool for the design of improved structures.