Energy- and time-dependent dynamics of trap occupation in 4H-SiC MOSFETs

A methodology for characterizing the transient response of 4H-SiC MOSFETs has been developed. The method combines new physical models, simulation techniques, and experiment to provide insight into the details of MOSFET time-dependent dynamics. A new physical model for generation-recombination between interface traps and channel electrons was derived, facilitating the analysis of trap dynamics in the energy, space, and time domains. A set of algorithms was developed, which enabled these rates to be incorporated into the drift-diffusion model so that their effect on the switching of 4H-SiC MOSFETs could be numerically evaluated. The correlation of simulated and experimental dc and transient drain current allowed the extraction of the density and the effective capture cross sections of interface traps. It was found that states near the band edge would become occupied much more quickly and had a much larger effective capture cross section than those that were several tenths of an electronvolt away from the band edge. This has led to the conclusion that the fast traps with large capture cross sections are likely to be interface states, whereas the traps with the smaller capture cross sections are a combination of midgap interface states and oxide traps. The observation of trap dynamics suggests that improvements in long-term device stability can be achieved by reducing oxide traps, whereas short-term stability can be improved by the reduction of interface traps.