Two-dimensional numerical investigation of the impact of material-parameter uncertainty on the steady-state performance of passivated 4H-SiC thyristors

We calculated the impact of inaccurate values of the free-carrier lifetime, SiC/SiO2 interface recombination velocity and interface charge, dopant ionization energy, electric permittivity, impact ionization rates, saturation velocity and field-dependent mobility on the holding current, switching current, and breakover voltage at different applied gate currents for an interdigitated 4H-SiC thyristor with two-dimensional steady-state numerical simulations. We observed that free-carrier lifetimes, interface charge and recombination velocity, and impurity ionization energy have the greatest impact on thyristor performance. As the carrier lifetime increases, the holding current decreases and the results logarithmically approach a single I-V curve in the negative differential resistance region. Comparing interface charge and recombination velocity, we demonstrated that recombination velocity has a larger effect on the holding current, but interface charge has a larger effect on the breakover voltage. Also, deeper acceptors increase the holding current, while deeper donors decrease the holding current. Our results demonstrate that mapping the negative differential resistance region by plotting the breakover voltage for different applied gate currents can give valuable information on the device and material properties. The experimentally observed nonuniform changes in the breakover voltage and switching current for uniform gate current steps are explained. The results indicate that interface properties must be included when simulating turn-on and turn-off by gate control. The results also indicate that the free-carrier lifetime variations that occur across a wafer can lead to large differences in the performance of two devices that are expected to have undergone identical processing. (C) 1998 American Institute of Physics. [S0021-8979(98)03220-4]