Time Dependent Trapping and Generation-Recombination of Interface Charges: Modeling and Characterization for 4H-SiC MOSFETs

SiC MOSFETs have very large interface trap densities which degrade device performance. The effect of traps on inversion layer mobility and inversion charge concentration has been studied, and mobility models suitable for inclusion in Drift-Diffusion simulators have been developed for steady state operation of SiC MOSFET devices. Here, we attempt to model the transient behavior of SiC MOSFETs, and at the same time, extract the time constants for the filling and emptying of interface traps. As compared to the inversion layer, interface traps in SiC MOSFETs are slow in reacting to change in gate bias. So, at the positive edge of a gate pulse, we see a large current in the MOSFET, which then decays slowly to the steady state value as the interface traps fill up. We have developed a generation/recombination model for minority carriers in a SiC MOSFET based on the Shockley-Read-Hall recombination model for electrons and holes. In our model, the generation/recombination takes place between minority carriers in the inversion layer, and the traps at the SiC-SiO2 interface. Comparing our simulated current vs. time curves to experiment, we have been able to extract time constants for the filling and emptying of traps at the SiC-SiO2 interface.