Time-gated optical spectroscopy of field-effect-stimulated recombination via interfacial point defects in fully processed silicon carbide power MOSFETs

Fully processed SiC power MOSFETs emit light during switching of the gate terminal, while the drain and source terminals are both grounded. The emitted photons are caused by defect-assisted recombination of electrons and holes at the $4H$-$\mathrm{([A-Z][a-z])([A-Z])}/{\mathrm{([A-Z][a-z])([A-Z])}}_2$ interface, and can be detected through the SiC substrate. Here we present time-gated spectroscopic characterization of these interfacial point defects. Unlike in previous studies, the devices were opened in such a way that the drain contact remained electrically active. A separate examination of the photons emitted at the rising and falling transitions of the gate-source voltage enabled the extraction of two different spectral components. One of these components consists of a single transition with phonon replicas of a local vibrational mode with an astonishingly high energy of 220 meV—well above the highest phonon modes in $4H$-SiC and ${\mathrm{([A-Z][a-z])([A-Z])}}_2$ of 120 and 137 meV, respectively. On the basis of a quantum mechanical model, we successfully fitted its emission spectrum and assigned it to donor-acceptor-pair recombination involving a carbon-cluster-like defect. Other transitions were assigned to ${\mathrm{EH}}_{6/7}$-assisted, ${\mathrm{EK}}_2$-D, and nitrogen-aluminum donor-acceptor-pair recombination. Because of the relevance of these defects in the operation of SiC MOSFETs, these insights will contribute to improved reliability and performance of these devices.