Filamentation and blow-up ignition in p-n-p-n devices

We analyze a symmetric double-gated thyristor, in which electrons and holes are admitted to behave symmetrically on the corresponding sides of the central junction plane. By further imposing that the carrier transit times depend on the drift field, we arrive at a non linear partial differential equation that describes the transverse behaviour and admits blow-up type solutions leading to current filamentation, a possible explanation for hot spots. Results obtained by the solution of the continuity and Poisson equations by finite difference come in support of this theory. We also predict the shortening of the bases during thyristor switching, associated with high drift fields expanding from the central junction towards the cathodic junction. These results could provide a simple interpretation for experimental data in GTOs published by other authors.