On the Need for Accurate Experimental Determination of the Impact Ionization Coefficients Along <1120> Direction in 4H-SiC

We analyze the sensitivity of breakdown voltage of 4H-SiC superjunction (SJ) devices for variations in the impact ionization coefficients (IICs) along the $\lt 11 \overline{2} 0\gt$ direction. While there are several works that provide experimentally determined IICs along $\lt 0001\gt$ and they closely match with each other, there exist only two works that provide IICs along $\lt 11 \overline{2} 0\gt$ and they differ significantly. As the breakdown voltage in 4H-SiC depends strongly on the anisotropy of IICs, we show that the mismatch in the IICs along $\lt 11 \overline{2} 0\gt$ results in about $20 \%$ deviation in simulated breakdown voltage, thus calling for experimental works with universal agreement.