the effective doping profile of a finished thyristor is altered with helium ions radiated into a region provided for triggering the thyristor in such a way that the breakover voltage for overhead ignition is increased or reduced . doping profile changes made in the cathode side half of the anode side base provide effective results , e . g . in the vicinity of the pn junction between the anode side and the cathode side base . the helium ions generate acceptor - type states that lower the effective n doping .