Carrier lifetime and turn-off current control by electron irradiation of MCT

Abstract

Lifetime control in power devices is an effective means of their speeding. To reduce the turn-off time of such devices, irradiation with fast electrons may be used. The main advantage of the electron irradiation as a means of lifetime control is the possibility to irradiate the devices after their packaging. Required characteristics of devices can be finally adjusted by varying the dose given to them. An MOS controlled thyristor (MCT) with a blocking voltage of 3000 V was used to demonstrate the possibilities offered by this method. Before irradiation, the turn-off time of the MCT was 30 μs . After irradiating the thyristor with 2 MeV electrons up to the dose 5×10 12 cm −2 , the turn-off time was reduced to 2.5 μs . The on-voltage was increased to 7.5 V at a highest controlled current density of 160 A/ cm 2 . The experiments showed that, using electron irradiation, it is possible to control the minority carrier lifetime in the range between 30 and 2 μs with acceptable increase in the on-voltage (from 2.8 to 7.5 V). The most interesting consequences of the above treatment were an increase in the current density which could be controlled by the thyristor (up to 160 A/ cm 2 ) and the possibility of device operation at a total current of 55 A. Thermal stability of the radiation-reduced changes was compared with the case of proton-irradiated MCT crystals.