Carrier Generation Lifetimes in 4H-SiC MOS Capacitors

The field of SiC electronics has progressed rapidly in recent years, but certain electronic properties remain poorly understood. For example, a consensus has not been reached as to the specific point defects which limit minority carrier recombination, and little is known about defects which limit generation lifetimes. This paper investigates generation lifetimes using the pulsed MOS capacitor technique and compares the results with defect densities, recombination lifetimes, and Schottky diode characteristics in the same material for the first time. Carrier generation lifetimes in 4H-SiC epilayers range from less than 1 ns to approximately 1 μs and depend strongly on measurement conditions and data interpretation. They are limited by dislocations only at densities higher than 10⁶ cm^-2.The only point defect that is theoretically capable of limiting generation lifetime to the levels currently observed in 4H-SiC is EH 6/7. However, this defect cannot account for the case where generation lifetimes are lower than recombination lifetimes in the same area. This is not seen in silicon and seems to be inconsistent with theory. Possible reasons for these perplexing results are discussed, and it is attempted to form a framework with which further understanding of the significance of carrier generation lifetime measurements in SiC can be achieved.