Holding current and switch-on mechanisms in 12 kV, 100 A 4H-SiC optically triggered thyristors

Abstract

Temperature dependence of the holding current has been studied in high-voltage (12 kV class) 4H-SiC optically triggered thyristors in the temperature range from 300 to 425 K. The holding current Ih monotonically decreases with increasing temperature T due to two factors: enhanced thermal ionization of comparatively deep Al acceptors in the p+ emitter and increasing carrier lifetime in the blocking p base. The Ih(T) dependence reveals the existence of a ‘weak point’ within the optical window, which is characterized by a substantially smaller critical charge than that within the remaining part of the window. Analysis of the Ih(T) dependence confirms that high-voltage SiC thyristors are switched-on at room temperature only at a high injection level in the blocking base. At elevated temperatures, the same thyristor is switched on by the ‘classical’ mechanism typical of Si thyristors. Effective shunting of the p++–n emitter junction affects the properties of the thyristor. Possible effective-shunting mechanisms are discussed.