Simulation study of on-state losses as function of carrier life-time for a GaN/SiC high power HBT design

SiC has several properties that makes it more suitable than silicon for high power devices. One problem with SiC bipolar devices is the short carrier life times, and this problem becomes more severe when designing devices for high voltage applications since the dimensions are larger. This work investigates how the Shockley-Read-Hall lifetime influences the on-state characteristics of a HBT or BJT switch in 4H-SiC. The on-state characteristics were simulated with varying SRH lifetimes in the base and drift region. Comparisons were made at 100A/cm(2) collector current density, J(C), and at the base current density, J(B), where the total on-state power loss of the design is at minimum. The SRH lifetime in the drift region is the dominant parameter for on-state performance, whereas the SRH lifetime in the base is of much less importance, The simulations showed that to reach an acceptable J(C)/J(B)-ratio of 100 at power minimum a SRH. lifetime of at least 100 mu s in the drift region was needed for the HBT design This lifetime is far from the experimental values reported for 4H-SiC. The advantages of the heterojunction in comparison to ordinary BJTs decreases with shorter SRH lifetimes, but an improvement could always be seen.