An advanced physical model for the Coulombic scattering mobility in 4H-SiC inversion layers

In this work, a new model for the mobility due to Coulombic scattering by interface charges (⁠$μC$⁠) in 4H-SiC MOS structures, which is suitable for device study via finite element (FE)-based simulations, is proposed. Unlike popular expressions based on the classical Sah–Lombardi model which lead to major inconsistencies in $μC$’s variation with the semiconductor depth $z$⁠, the proposed model combines previous experimental data with established theoretical results on $μC$’s depth dependence. The evolution of the components of the channel drift mobility (⁠$μch$⁠) with $z$ and the gate bias $Vgs$ is then examined using this model by means of FE analysis. It is found that while $μC$ is the dominant component at the surface, at larger depths $μch$ is determined by the mobility due to acoustic phonon scattering (⁠$μSA$⁠). Moreover, at low channel dopings (⁠$NA$⁠) or temperatures above approximately $425K,μSA$ replaces $μC$ as the key limitation. Conversely, the roughness scattering mobility $μSR$ becomes important only at very high $Vgs$ and $NA$⁠.