Effects of nuclear radiation on a high-reliability silicon power diode—4. Analysis of reverse bias characteristics

Abstract

We present device characteristics obtained from two-dimensional numerical simulations of asymmetric 4H-SiC gate turn-off (GTO) thyristor structures. Material parameters are discussed, and a good comparison with measured results is demonstrated. Current vs voltage characteristics indicate that typical structures have quite good electron injection from the cathode, but hole injection from the anode is weak unless the n-base layer is doped less than 1×1018 cm−3. On the other hand, lowering electron injection at the cathode/p-base junction is important to improve the turn-off gain. The 2000 V blocking structure simulated with lifetimes of τn:τp=100:50 ns does not reach its on-state for current densities less than 6000 A/cm2, but for lifetimes of 400:200 ns, this minimum is reduced to 1 A/cm2. Blocking voltages increased approximately 400 V for a 3 μm increase in the drift region length. Clamped inductive load mixed-mode simulations with a 4H-SiC flyback diode indicate that the peak power during turn-on is only slightly higher than during turn-off when switching a 4 Ω, 5 mH load. Because turn-on times are much shorter than turn-off times, much less power is dissipated during turn-on for both 27°C and 200°C ambient temperature operations.