Numerical investigation of the thyristor forward characteristic

Analytical solutions for the forward characteristic of thyristors have been limited to abrupt and constant doping profiles. Average values for the mobilities and the carrier lifetime had to be assumed for each region of the device. Results will be presented here which are based on an exact numerical solution of the transport, continuity, and Poisson equations for the one-dimensional thyristor. Doping, mobility, and lifetime can be varied from point to point. Thyristor structures are much wider and higher doped than the devices treated numerically in the literature. The dependency of the forward characteristic on various device parameters was examined, and the important results were verified experimentally. For high current and a base width that is large compared to the diffusion length, the dependency of mobility on the carrier concentration leads to a base voltage drop significantly lower than that expected from analytical theory. Furthermore, it is shown that for this case the parameters of the highly doped side regions (doping, width, and lifetime) have much less influence than predicted from Herlet's [3] theory.