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 N
₂
O. The interface trap density D
_it
was determined close to the conduction band edge by Hall effect measurements to be 2?10
¹³
cm
^-2
? eV
^-1
in the N
₂
O-based oxide sample and 1?10
¹¹
cm
^-2
? eV
^-1
in 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 N
₂
O 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 N
₂
O 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?10
¹²
cm
^-2
) deeper in the bandgap compared to MOSFETs with gate oxides thermally grown in N
₂
O (1.4?10
¹²
cm
^-2
). A maximum Hall mobility of 65 cm
²
/V ? s was measured in the SEO-based MOSFET, and 16 cm
²
/V ? s was measured on the N
₂
O 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.