Investigation of the Universal Mobility of SiC MOSFETs Using Wet Oxide Insulators on Carbon Face With Low Interface State Density

Abstract

The universal mobility of SiC MOSFETs has been investigated. SiC MOSFETs with the gate oxide formed by wet oxidation have been fabricated on 4H-SiC ( $000\overline {\textsf {1}}$ ) substrates to reduce Coulomb scattering sources. In order to suppress charge trapping in the gate oxide during measurement, surface carrier concentration ( ${N}_{s}$ ), and channel current have been evaluated from the transient characteristic of source current and drain current under the application of pulse gate bias. To eliminate the influence of charge trapping in interface states, the concentration of electrons trapped in interface states has been estimated and subtracted from ${N}_{s}$ . Effective channel mobility ( $\mu _{\textsf {eff}}$ ) and effective electric fields ( ${E}_{\textsf {eff}}$ ) have been calculated from the ${N}_{\textsf {s}}$ and channel current. The substrate impurity concentration ( ${N}_{A}$ ) and substrate bias ( ${V}_{b}$ ) dependence of $\mu _{\textsf {eff}}$ – ${E}_{\textsf {eff}}$ characteristics have been investigated, and, as a result, it has been confirmed that $\mu _{\textsf {eff}}$ of SiC MOSFETs shows a universal characteristic as a function of ${E}_{\textsf {eff}}$ at high ${E}_{\textsf {eff}}$ , independent of ${N}_{\textsf {A}}$ and ${V}_{\textsf {b}}$ . In addition, we have investigated the temperature dependence of this universal mobility in the range of 223–423 K, and formulated the result in a simple model. This result leads to a better understanding of electron transport properties in SiC inversion layers and the improvement of the accuracy of device and circuit simulations of SiC MOSFETs.