Why is fast recovery diode plasma-engineering with ion-irradiation superior to that with emitter efficiency reduction?

This paper presents the comparison of two 4.5 kV diodes with expanded safe operating area (SOA) in terms of an expansion to higher line voltages. In order to improve the reverse recovery characteristic the excess carrier concentration close to the anode during the on-state has to be reduced. To control the injection efficiency of the anode two state of the art technologies, the reduction of the emitter doping and the ion irradiation in the p-doping region, are compared in this paper. The local lifetime control technique is shown to have major advantages compared to the emitter doping reduction technique in terms of up to 50% lower switching losses at recovering from low forward current densities (e.g., 2 A/cm/sup 2/). This improvement was obtained on devices with identical on-state characteristic. Additionally, a softer switching behavior is observed for the ion-irradiated diodes. An explanation for this experimentally found behavior is provided by calibrated computer simulations.