Spreading velocity of the active area boundary in a thyristor

The modeling, measurement, and magnitude of the plasma-spreading velocity in a modern thyristor structure is discussed. A simple model based on lateral fields present in the p-base of the thyristor is derived. This model is compared with a diffusion model by examining the validity of their predictions. Data on the effects of variations in radial position, current density, temperature, base widths, cathode-emitter short density, and gold recombination site density are presented. Basically, the data show that the spreading velocity is l) independent of radial position 2) a linear function of the log of the current density, 3)increased with increasing temperature, 4) increased with decreasing p-base width, 5) decreased cathode emitter short density, and 6) decreased recombination site density. The derived model is shown to provide a reasonable explanation for these effects which is qualitative and in some cases quantitative.