Dipole Scattering at the Interface: The Origin of Low Mobility observed in SiC MOSFETs

TL;DR

This paper investigates the cause of low electron mobility in SiC MOSFETs, concluding that electric dipoles at the interface are the dominant scattering mechanism responsible for the observed low mobility.

Contribution

It identifies electric dipoles at the interface as the primary cause of low mobility in SiC MOSFETs, ruling out phonon and Coulomb scattering through theoretical comparison.

Findings

Dipole scattering explains the effective field dependence of mobility.

High density of interface dipoles correlates with low mobility.

Theoretical mobility matches experimental observations when dipole scattering is considered.

Abstract

In this work, the origin of the low free electron mobility in SiC MOSFETs is investigated using the scattering theory of two-dimensional electron gases. We first establish that neither phonon scattering nor Coulomb scattering can be the cause of the low observed mobility in SiC MOSFETs; we establish this fact by comparing the theoretically calculated mobility considering these effects with experimental observations. By considering the threshold voltages and the effective field dependence of the mobility in SiC MOSFETs, it is concluded that the scattering centers of the dominant mechanism are electrically neutral and exhibit a short-range scattering potential. By considering charge distribution around a neutral defect at the interface, it is established that an electric dipole induced by the defect can act as a short-range scattering potential. We then calculate the mobility in SiC MOSFETs assuming that there exist a high density of dipoles at the interface. The calculated dipole-scattering-limited mobility shows a similar dependence on the effective field dependence to that observed in experimental results. Thus, we conclude that scattering induced by a high density of electric dipoles at the interface is dominant cause of the low mobility in SiC MOSFETs.