2-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 life time, SiC/SiO2 interface recombination velocity and interface charge, dopant ionization energy, electric permittivity, impact ionization rat es, saturation velocity and field-dependent mobility on the holding cu rrent, switching current, and breakover voltage at different applied g ate currents for an interdigitated 4H-SiC thyristor with two-dimension al steady-state numerical simulations. We observed that free-carrier l ifetimes, interface charge and recombination velocity, and impurity io nization 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 di fferential resistance region. Comparing interface charge and recombina tion velocity, we demonstrated that recombination velocity has a large r effect on the holding current, but interface charge has a larger eff ect on the breakover voltage. Also, deeper acceptors increase the hold ing current, while deeper donors decrease the holding current. Our res ults demonstrate that mapping the negative differential resistance reg ion by plotting the breakover voltage for different applied gate curre nts can give valuable information on the device and material propertie s. The experimentally observed nonuniform changes in the breakover vol tage and switching current for uniform gate current steps are explaine d. The results indicate that interface properties must be included whe n simulating turn-on and turn-off by gate control. The results also in dicate that the free-carrier lifetime variations that occur across a w afer can lead to large differences in the performance of two devices t hat are expected to have undergone identical processing. (C) 1998 Amer ican Institute of Physics. [S0021-8979(98)03220-4]