Light-triggering phenomena on thyristors with an n-emitter layer over the light-sensitive gate area

Turn-on phenomena of a light-activated thyristor are analyzed using a one-dimensional numerical model that consists of the full set of semiconductor device equations, including the optically generated current and the effect of the shorted emitter. Results indicate that the photocurrent Ipis induced by photovoltaic effects of the junction and that its flow is in the reverse direction of the anode current IA. Consequently, Ipcirculates through the p-base, the short path placed across the junction and the n-emitter resulting in a contribution to the light triggering, in addition to that of IAcaused by the conventional transistor action. In order to confirm the predicted behavior of the photocurrents, light-triggered 4-kV devices were fabricated. The experimental results thus obtained confirm the conclusions drawn from the model analysis.