Specific features of switch-on processes in high-voltage (18 kV class) optically triggered 4H-SiC thyristors

A computer simulation has been carried out to analyze and explain the specific features of the switch-on process in super-high-voltage (18 kV class) optically triggered 4H-SiC thyristors. It is shown that the previously experimentally observed two-stage character of the switch-on processes can be understood in a one-dimensional approach. The two-stage turn-on of the 18 kV structures is accounted for by the rather slow current rise in the structure with a very wide (160 µm) blocking base. In full agreement with the experimental results, a simulation in the frame of the same approximations demonstrated that, in the 12 kV class thyristor structures with a blocking base thickness of 90 µm, the current increases monotonically during the switch-on process. (paper)