# A Simulator for Investigation of Breakdown Characteristics of SiC MOSFETs
## 3 Results and Discussion
### Evaluation of the Device Geometry  
Since the lattice temperature has less impact on the BV, following simulation, we fixed the lattice temperature constant at 300 K. Figure 7 plots the BV curves for devices with different radii of the curvature at the base corner (RBase corner), as shown in Figure 2. The results show that a significant increase in the ON-state current occurring as the bottom of the P base region changes from a right angle to an arc. As the curvature of the arc increases, there is no significant change in the ON-state current. Alongside that, BV decreases  
Figure 5: (**a**) Breakdown characteristic curves (inset: output characteristics of Vds between 0 and 100 V at Vgs = 10 V) and (**b**) transfer characteristic curves with different lattice temperatures. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Temperature (K)** & **Vth (V)** & **SS (mV/dec)** \\ \hline
300 & 4.57 & 112.04 \\
473 & 4.32 & 172.85 \\
573 & 4.22 & 206.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Vth and SS values under different lattice temperatures. significantly as the radius of curvature at the base corner increases when Vgs = 10 V and T = 300 K. Specifically, the BV with a radius of 5 \(\upmu\)m undergoes a 21% decrease compared to that with a radius of 0 \(\upmu\)m. The increase in curvature causes a higher current density, which increases the impact ionization rate, as shown in Equation (5), which in turn reduces the breakdown voltage. Figure 8 illustrates the impact ionization rate distribution for different corner curvature radius at the base region. Figure 8a,b presents the impact ionization rate before and after breakdown for a radius of 0 \(\upmu\)m, respectively. The peak impact ionization rate occurs near the top interface between the P base and N drift region, with peaks of 3.6 \(\times\) 10\({}^{20}\) cm\({}^{-3}\)/s and 7.7 \(\times\) 10\({}^{23}\) cm\({}^{-3}\)/s, respectively. The variation in the distribution of the impact ionization rate clearly elucidates the breakdown process as Vds increases from 2.4 kV to 2.5 kV at Vgs = 10 V. The contour where the impact ionization rate reaches 10\({}^{23}\) cm\({}^{-3}\)/s, as demonstrated in Figure 8b, corresponds to the current flowing from the N+ region to the N+ substrate, as shown in Figure 6b. Figure 8c presents the impact ionization rate distribution with a corner curvature of 5 \(\upmu\)m. Notably, the contour range with a value of 10\({}^{23}\) cm\({}^{-3}\)/s (dashed line in Figure 8b,c) is significantly broader than that in Figure 8b, indicating that increasing the curvature of the base region corner leads to the electrons being more concentrated on the lower side of the base region, thereby reducing the BV. Figure 9 presents both the current density distribution associated with corner curvature radii of 5 \(\upmu\)m and 1.2 \(\upmu\)m at the base region, as well as the distribution of the electric field at y = 20 \(\upmu\)m. An evident observation is the substantial widening of the current flow path in Figure 9a,b, in contrast to the case with a radius of 0 \(\upmu\)m, as depicted in  
Figure 6: Distributions of current density at (**a**) Vds = 2.4 kV and (**b**) Vds = 2.5 kV and Vgs = 10 V when T = 300 K.  
Figure 7: Breakdown characteristic curves with different radii of the corner curvature at the base region at T = 300 K and Vgs = 10 V. (insets: schematic cross-sections with R of 0 \(\upmu\)m and 5 \(\upmu\)m). Figure 6b. Comparing the dashed lines in Figure 9a,b, a wider current density in the region of 15-17.5 \(\upmu\)m can be seen when radius = 5 \(\upmu\)m. This observation further explains the difference in BV when the radius exceeds 0 \(\upmu\)m, as illustrated in Figure 7. The electric field distribution in Figure 9c indicates that the electric field strength does not decrease significantly as the radius increases.