Optical Emission Correlated to Bias Temperature Instability in SiC MOSFETs

Bias Temperature Instability refers to the widely known shift of the threshold voltage of metal-oxide-semiconductor field-effect transistors upon changes of gate bias and is typically measured at room temperature or above. The shift of the threshold voltage is caused by trapping/detrapping of charges in pre-existing defects located close to the semiconductor-insulator interface as well as the generation of new defects. Particularly silicon carbide transistors show a pronounced short-term trapping/detrapping behavior, which leads to threshold voltage variations already well below the microsecond time frame after gate bias changes. The physics of involved charge transfer reactions has been accurately described by non-radiative multiphonon transitions. We present evidence that in SiC devices radiative charge transitions are also present in a Bias Temperature Instability experiment, once the transistor is switched between accumulation and inversion or vice versa. Furthermore, we present a field-effect based pump-probe measurement that allows us to correlate the number of emitted photons after microsecond gate pulses to the threshold voltage recovery.