Minimisation of current crowding during turn-off of power GTO devices

The maximum controllable anode current is influenced by the current crowding phenomenon observed in GTO thyristors during turn-off. This phenomenon initiates: (1) formation of the current filament with a density much higher than its surrounding and leads to the localised thermal instability; and (2) conductivity modulation at the conduction channel causing a nonuniform electric field distribution within the depletion layer and resulting in an early punchthrough breakdown. In this paper, device parameters are optimised by detailed two-dimensional device simulations to minimise the current crowding and at the same time to maintain a low forward voltage drop and short turn-off time. By doing so, the localised thermal stress can be reduced and a more uniform electric field distribution is obtained