The dynamics of the thyristor turn-on process

The study of the thyristor turn-on process has been an area of on-going study both theoretically and experimentally. The importance of the turn-on process occurs because of the desireability of achieving (at specific gate drive) a uniform turn-on line within a predictable turn-on delay and at a specific rate of increase of anode current. In spite of its importance, there is little information about the details of the turn-on process, particularly the early stages of the process, until the anode current begins to flow. The problem is that it is extremely difficult to monitor carrier levels within the device before they reach levels about 10¹⁶cm^-3, using any of the infrared emission or absorption techniques. At this point, however, the delay phase is over and the spread of the carrier plasma is well underway. In order to investigate the early phases of operation, a theoretical investigation was undertaken. For this paper, the four layer thyristor structure will be analyzed using exact numerical solutions of the full set of semiconductor device equations in two dimensions and time. Details of the model are available elsewhere (1). It will be shown that the turn-on process consists of an initial turn-on phase, a N base delay phase, a P base delay phase, and finally the anode current build up phase.