Numerical simulation of avalanche photodiodes with guard ring

A numerical modelling of SAM-APDs which takes into account the effects of the guard ring on the electric field profile is presented. Starting from the knowledge of the technological parameters and from a one-dimensional model, for which Poisson´s and continuity equations have been treated, the authors calculate the gain, the dark current, and the cut-off frequency of the device, so that it is possible to deduce the limits of those parameters to avoid parasitic breakdowns at the centre of the diode, and to get structures with high gain-bandwidth products. A two-dimensional model based on numerical solution of Poisson´s equation to study the electric field profile under the guard ring is developed. Optimal conditions for implantation are deduced to avoid breakdown at the edge of the junction curvature. The results given by this modelling are compared with the experimental results concerning SAM-APDs with guard ring, which have been fabricated by CIT ALCATEL