Trap and inversion layer mobility characterization using Hall effect in silicon carbide-based MOSFETs with gate oxides grown by sodium enhanced oxidation

Low-temperature MOS-gated Hall measurements and gated diode capacitance-voltage (C-V) measurements were performed to characterize both trap density and Hall mobility on 4H-silicon carbide MOSFETs with gate oxides grown by sodium enhanced oxidation (SEO) and thermally grown in N₂O. The interface trap density D_it was determined close to the conduction band edge by Hall effect measurements to be 2 × 10¹³ cm^-2 · eV^-1 in the N₂O-based oxide sample and 1 × 0¹¹ cm^-2 · eV^-1in the SEO sample. The presence of these interface trap states above the conduction band edge suggest that they are near interface oxide trap states rather than conventional fast interface trap states. The threshold voltage changes with temperature in MOSFETs with gate oxides grown thermally with N₂O but not significantly in MOSFETs with gate oxides grown by SEO. The superior threshold voltage stability at low temperatures in the SEO-based MOSFET compared to the N₂O oxidation-based MOSFET is due to lower trap density near the conduction band edge. Gated diode C-V measurements showed that MOSFETs with gate oxide grown by SEO had a higher density of interface traps 2.2 × 10¹² cm^-2 deeper in the bandgap compared to MOSFETs with gate oxides thermally grown in N₂O1.4 × 10¹² cm^-2. A maximum Hall mobility of 65 cm²/V · s was measured in the SEO-based MOSFET, and 16 cm²/V · s was measured on the N₂O oxidation-based MOSFET at 225 K. The mobility correlates well with the interface trap density close to the conduction band edge as measured by Hall effect measurements but does not correlate with gated diode C-V measurements of traps deeper in the band gap. Temperature-dependent gated Hall mobility measurements were used to show that the inversion layer mobility in the SEO samples were limited by Coulomb scattering from interface trapped charge and surface roughness scattering but not by phonon scattering.