  MOSFETs based on wide band-gap semiconductors are suitable for operations at
high temperature, at which additional atomic-scale processes that are benign at
lower temperatures can get activated which results in device degradation.
Recently significant enhancement of electron trapping was observed under
positive bias in SiC MOSFETs at temperatures higher than 150{\deg}C. Here we
report first-principle calculations showing that the enhanced electron trapping
is associated with thermally activated capturing of a second electron by an
oxygen vacancy in SiO2, by which the vacancy transforms into a new structure
that comprises one Si dangling bond and a bond between a five-fold and a
four-fold Si atoms. The results suggest a key role of oxygen vacancies and
their structural reconfigurations in the reliability of high-temperature MOS
devices.
