Turn-on phenomena in optically and electrically fired thyristors

An analytical solution of the time-dependent transport equation including surface recombination and optical injection for a diffused thyristor base is presented. By means of the classical two-transistor model, the turn-on transient may be predicted. Apart from the influence of technological parameters like base width, doping profile, and diffusion length, the effect of optical versus electrical injection as well as surface recombination are discussed. Surface recombination may significantly influence the optical turn-on threshold. Despite the rigorous simplicity of the model, the dynamic turn-on behavior of an optically fired high-voltage thyristor is in very good agreement with the experiment. The data, being presented for a wide range of parameters, are useful for practical design.