A field controlled thyristor having its base doped more lightly near the gate than near the anode achieves a low forward voltage drop, high blocking gain, and fast switching speed at any given forward blocking voltage rating. Although the high resistivity region around the gate area allows the device...http://www.google.com/patents/US4937644?utm_source=gb-gplus-sharePatent US4937644 - Asymmetrical field controlled thyristor
