“Paradoxes” of carrier lifetime measurements in high-voltage SiC diodes

For Silicon Carbide (SiC) high-voltage rectifier diodes, contradictions appear when the most important parameter of the diodes, the minority carrier lifetime, is measured by different techniques. A qualitative analysis and a computer simulation have been carried out to clarify the origin of these contradictions. For 4H-SiC p⁺n diodes with 6 kV blocking capability, data on residual voltage drop at high current densities, switch-on time, reverse current recovery, and post-injection voltage decay are analyzed. It is shown that the whole set of experimental data can be explained by the existence of a thin (l~0.1 μm) layer near the metallurgical boundary of the p⁺n junction with very small carrier lifetime τ_l that is essentially smaller than the carrier lifetime τ across the remaining part of the 50-μm n-base. It is emphasized that the existence of such a layer allows, under certain conditions, the combination of a relatively low residual forward voltage drop and very fast reverse recovery. Approaches to minority carrier lifetime measurements are discussed