High-temperature physical effects underlying the failure mechanism in thyristors under surge conditions

With the aim of assessing the role of various high-temperature physical effects in the transient electrothermal behavior of thyristors under surge current conditions, the distribution of carriers concentration in the bases of a thyristor at temperatures close to the threshold of the device destruction has been estimated in a quasi-static approach. It was found that the carriers concentration in almost the entire bases region is well below the level when the Auger recombination and carrier-carrier scattering are important. It is shown that the drastic fall of mobilities µ at elevated temperatures T is responsible for the removal of both Auger recombination and carrier-carrier scattering from the bases of devices. Becoming the dominant factor regulating the carriers dynamics in the bases, it is precisely the dependence \mu = f(T) which renders important the contribution of intrinsic carriers in the inhomogenous supply of bases with mobile carriers under strong power dissipation. These high-temperature physical aspects axe incorporated into an unitary presentation of phenomenology of thyristors failure under surge current conditions. The theoretical/experimental background confirming the validity of the failure model presented herein is also outlined in this work. It is shown that the advanced model allows for a computer-based prediction of the transient electrothermal behavior of power thyristors under various surge ratings.