Extraction of trapped charge in 4H-SiC metal oxide semiconductor field effect transistors from subthreshold characteristics

A technique for characterizing trapped charge in silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) based only on the subthreshold I-V characteristics and its degradation under bias temperature stress is described. The method utilizes the large departure of the subthreshold slope from a constant value, due to large and exponentially rising DIT (density of interface traps) near band edges for SiC/SiO2 interface. Elevated bias-temperature stress experiments demonstrate the feasibility of separating ΔNIT (increase in interface trapped charge) from slow trapping components like ΔNOT (increase in oxide trapped charge) with minimal error due to extrapolation of subthreshold current to midgap potentials. A slow trap, dissimilar to either interface or oxide states close to the interface, dominates degradation at elevated temperature.