Suppression of charge accumulation on termination area of 4H-SiC power devices

Passivation films on the termination area of 4H-SiC diodes were investigated to clarify the origin of a positive charge accumulation that induces instability of the breakdown voltage. A method to differentiate measured depletion layer capacitance is proposed as a way to analyze the positive charge density after applying voltage stress. Samples with different passivation films were fabricated to compare the effects of the passivation films. The results of analyzing three kinds of passivation film show that the charge density did not increase in the sample without SiO2 on the termination area. In addition, the breakdown voltage of the sample did not change after applying stress. The results suggest that the passivation film sample without SiO2 is effective for suppressing the accumulation of positive charge density.