Fast recovery radiation enhanced diffusion (RED) diode: Palladium versus platinum

Modern power switches require the complementary diodes which are robust at the turn-off of ever higher currents at higher di/dts and supply voltages. A new technology to increase the ruggedness of free-wheeling and clamping diodes, which is based on the radiation enhanced diffusion (RED) of palladium, has been recently developed. In this work, the RED technology of palladium is confronted with that of the platinum. Silicon P-i-N diodes (V_br = 2500 V, Area = 2 cm², positive bevel, press pack contact) were subjected to the RED of Pd and Pt in the temperature range between 500 and 800 0C to locally control the carrier lifetime and doping profile, if possible. The devices are compared in static (leakage, voltage drop) and dynamic parameters (unclamped low inductance reverse recovery). The RED of Pd is shown to create a low doped P-layer that postpones the dynamic avalanche towards higher line voltages and increases the static breakdown voltage. Platinum does not provide this feature and the lifetime reduction is smaller. While the dynamic parameters of the palladium RED diodes are greatly improved, those of the Pt have much higher maximal recovery current and poor SOA. In spite of the qualitatively similar electronic properties of the Pt and Pd deep levels, the accumulation of Pt in the region with radiation defects is found to differ quantitatively during the RED process in the temperature range 500-650 0C. The RED of Pt is therefore evaluated as unsuitable for the local lifetime control using the existing RED process.