Influence of passivation, doping and geometrical parameters on the avalanche breakdown of GaN SBDs

The breakdown of GaN-based Schottky barrier diodes associated with impact ionization events initiated by electrons injected by tunneling is physically analyzed by means of a Monte Carlo simulator self-consistently coupled with a two-dimensional solution of the Poisson equation. Simulations of a realistic topology where different geometrical parameters are modified allow to identify their influence on the breakdown voltage. The correct physical modeling of two-dimensional effects is essential for a proper prediction of the breakdown. Epilayer doping and thickness, dielectric used for the passivation and lateral extension of the epilayer are analyzed. As expected, the lower the doping and the thicker the epilayer, the higher the value found for the breakdown voltage, but, interestingly, the results also indicate that the peak electric field present at the edge of the Schottky contact, which may be reduced by means of high-k dielectric passivation and a short lateral extension of the epilayer, plays a key role in the breakdown.