A NEW INTERMEDIATE STATE MODEL FOR THE GTO - RELATION TO THE TURN-OFFPROCESS

An intermediate state of the GTO is treated, that is characterized sim ultaneously, by a negative gate current, high anode current, and rever se biases on parts of both the n+p and pn-junctions. This state provid es insight into the processes occurring during the storage and fall st ages of turn-off. The intermediate state exists when a negative gate c urrent is present that is insufficient to cause turn-off. Under these circumstances there exists a boundary layer between the squeezed highl y conducting on-region and the fully depleted off-region. It is this b oundary layer that provides most of the holes for the gate current. an d during the fall stage only this region is present. The mathematical approach is based upon quasistationary equations and a quasi-one-dimen sional approximation. The storage time, fall time and the width of the boundary region are obtained for both high and low-injection regimes This treatment is the first to clearly define the fall stage of turn-o ff.