Differences between platinum- and gold-doped silicon power devices

Both platinum and gold have been used to reduce lifetimes in fast recovery silicon power devices. There are substantial differences between the energy levels introduced by these impurities. Both impurities introduce acceptor levels which act to reduce hole lifetimes in n-type silicon; however, the gold acceptor is much deeper (Ec- 0.54 eV) than the corresponding platinum acceptor (Ec- 0.26 eV). In p-type material, on the other hand, the two impurities are quite similar; gold introduces a donor at Ev+ 0.35 eV, while the platinum donor is at Ev+ 0.32 eV. In terms of basic physics, this paper establishes guidelines to determine, for a given device type, which lifetime killer should be used to provide optimal performance. Platinum offers improved high-temperature properties and turn-on performance when compared to gold and is a better selection for devices which are switched so rapidly that the turn-off is governed mainly by the high injection lifetime. However, when the switching wave form involves low injection recombination tails, gold is a better choice than platinum.