Radiation-Enhanced Diffusion of Palladium for a Local Lifetime Control in Power Devices

Palladium (Pd) diffusion from a surface layer enhanced by defects from a helium (He) irradiation is shown to provide a local lifetime control in a power p-i-n diode annealed between 350degC and 700degC. An open-circuit voltage decay lifetime measurement is used to identify temperature ranges in which one of two lifetime control mechanisms takes part. Spreading resistance measurements show the doping compensation at the anode junction caused by defects after the Pd diffusion below 725degC. Locally modified doping profiles by introduced defects cause significantly lowered dynamic avalanche (DA) during fast reverse recovery compared to the standard He irradiation as confirmed also by device simulation. Advanced shaping of a shallow doping profile, reducing avalanche generation in the area of peaking electric field under a reverse bias, is suggested as an additional method to suppress the DA in power devices. The diffusion at 650degC gives the best static and dynamic parameters. Breakdown voltage and leakage current are those of untreated diode. Turn-off losses close to the SOA limit are also much lower than in the standard He irradiation, and thermal characteristics are better than after the traditional high-temperature diffusion.