Simulation of silicon n+np+, p+pn+ and Schottky TRAPATT diodes
Keywords: simulation, avalanche diodes, diffusion, minority carrier storage
AbstractThe plasma formation and extraction processes in silicon n+np+, p+pn+, and Schottky TRAPATT (TRApped Plasma Avalanche Triggered Transit) diodes were simulated. The drift-diffusion model was chosen for the simulation of the processes. We show that the minority carrier storage depends on the TRAPATT diode structure. The most intensive minority carrier storage takes place in the n+np+ diode, where holes accumulate in the n+ region and electrons in the p+ region. The extraction of electrons from the p+ region is more rapid due to higher electron mobility compared to holes. Thus, the initial current for the next oscillation period is the hole current. In the p+pn+ diode the accumulation of holes in the n+ region is inferior to that in the n+np+ diode due to a higher electric field in the pn+ interface. The initial current in p+pn+ diodes is lower and the voltage oscillation is almost periodic. The most efficient structure in respect to low minority carrier storage is a pm-type Schottky diode. In this structure the initial conditions in all voltage oscillation periods are the same and there is a quite periodic oscillation in a very wide region of the diode total current density. We show that periodic oscillation can be achieved even in the n+np+ diode with optical generation of the carriers during the plasma formation and extraction period.